Tonight’s Sky – September

The Greater Hazleton Area Astronomical Society

Full Corn Moon on September 1-2

Posted by Bruce McClure in TONIGHT | September 1, 2020

Above: Moonrise over Saltsjöbaden, Sweden. Image via Indranil Sinha.

Tonight – September 1-2, 2020 – presents the third and final full moon of our Northern Hemisphere summer (or Southern Hemisphere winter). In other words, this is the third of three full moons to occur in between the June 20 solstice and the September 22 equinox.

Click here to know the moonrise time, remembering to check the moonrise and moonset box.

Frequently, the September full moon provides the Northern Hemisphere with its Harvest Moon, because the September full moon – more often than not – is the closest full moon to the autumn equinox. But, in 2020, the first of two October 2020 full moons happens closer to this equinox, so this year’s Harvest Moon comes on October 1. When the September full moon is not the Harvest Moon, we in North America commonly call it the Fruit Moon, Corn Moon or Barley Moon.

The moon turns precisely full on September 2, 2020, at 5:22 UTC. At North American and U.S. time zones, that translates to September 2, at 2:22 a.m. ADT, 1:22 a.m. EDT, 12:22 a.m. CDT – yet on September 1, at 11:22 p.m. MDT, 10:22 p.m. PDT, 9:22 p.m. ADKT and 7:22 p.m. HST.Day and night side of Earth at full moon.

Day and night sides of Earth at the instant of full moon (2020 September 2 at 5:22 UTC). The shadow line at right (passing through Europe and Africa) depicts sunrise September 2, and the shadow line at left (going through northwestern North America) represents sunset September 1. Map via Earth View.

Astronomically speaking, the full moon occurs at a well-defined instant: when the moon is exactly 180o from the sun in ecliptic longitude (also called celestial longitude). That means the moon stands opposite the sun as measured along the ecliptic, which marks the sun’s annual pathway through constellations of the zodiac. Another way of putting it: at the instant of full moon, the moon-sun elongation equals 180 degrees. Click here to find out the present moon-sun elongation (if the number is positive, the moon is waxing; if negative, the moon is waning).

To the eye, though, the moon appears full for up to two or three days. So, no matter where you reside on the great globe of Earth, look for tonight’s moon to appear plenty full and colorful as it rises over the eastern horizon at dusk or very early evening.

Thereafter, the brilliant moon will beam all night long!

Bottom line: Full moon is September 2 at 5:22 UTC. Enjoy the 3rd and final full moon of northern summer (southern winter) tonight.

Look west after sunrise for the daytime moon

Posted by Deborah Byrd in TONIGHT | September 3, 2020

At top: Paul Schulz caught a daytime moon in September 2018, above and then behind Mt. Graham, Safford, Arizona. Thanks, Paul! Click here to view it larger.

The September 2020 full moon has passed. Now the moon is in a waning gibbous phase, which means it rises in the east later and later each evening. Beginning around the morning of September 3 or 4, 2020, look west after sunrise for the daytime moon.

So you’d look east before going to bed tonight to catch the moon over the eastern horizon. Then you’d look in the west after sunrise tomorrow, or in the next few mornings, to see the daytime moon over your western horizon.

Sylvia asked:

When is the best time to see the moon in the sky during daylight hours?

The answer is that a daytime moon is up there much of the time, but, because it’s pale against the blue sky, it’s not as noticeable as the moon at night.

The most noticeable moon at night is the one that stays out all night long. That would be around the time of full moon each month, when the moon is 180 degrees from the sun, or opposite the sun in our sky. Full moon was on September 2, 2020, at 5:22 UTC; translate UTC to your time.

A full moon rises around sunset and sets around sunrise. But now the moon is in a waning gibbous phase – rising later each night – and setting in the west later each day after sunrise.

At mid-northern latitudes in North America, the moon will set roughly two hours after sunrise on September 4, and will set about an hour later each day thereafter.

These recommended almanacs can help you find the moon’s setting time in your sky

By the way, the moon is up during the day half the time. It has to be, since it orbits around the whole Earth once a month. The crescent moon is hard to see because it’s so near the sun in the sky. At the vicinity of last quarter moon about a week from now, you might have to crane your neck, looking up, to notice it after sunrise.

Ordinarily, we don’t look up to see the waning last quarter moon and waning crescent after sunrise. That’s one reason why people so often miss the moon during the day.

Day by day, the lighted portion of the waning gibbous moon will shrink and the half-lit last quarter moon will come on September 10. Watch for the daytime moon to climb higher and higher into the western sky after sunrise all this coming week!

Jenney Disimon caught this daytime moon – a waning gibbous moon, 94.7 percent illuminated – from Sabah, North Borneo, on August 29, 2018.

Bottom line: Starting around the morning of September 3 or 4, 2020, look for the daytime moon in the west after sunrise!

See moon, Mars from September 4-6

Posted by Bruce McClure in TONIGHT | September 4, 2020

Moon near Mars on September 4, 5 and 6, 2020.

Around the world these next several evenings – September 4, 5 and 6, 2020 – watch for the waning gibbous moon and the red planet Mars to rise into your eastern sky a few to several hours after sunset. Once they’re up, these two worlds will be out for rest of the night.

As evening twilight ebbs into darkness, neither bright planet that comes out first thing at dusk/nightfall is Mars. Rather, they’re Jupiter and Saturn, with Jupiter being the brighter of two. Look for the moon and Mars to be up by mid-evening, by around 9 to 10 p.m. local time. If you have an obstructed eastern horizon, it could be a little later.Jupiter, Saturn and the Teapot beautiful the August 2020 evening sky.

Jupiter and Saturn climb highest up for the night around nightfall throughout September.

Every month, as the moon journeys full circle in front of the constellations of the zodiac, the moon sweeps by every solar system planet. For the fun of it, we also show the planet Uranus on our sky chart, but you probably won’t see this faint and distant planet without an optical aid. People with good vision, and a good knowledge of Uranus’ place in the heavens, can spot Uranus as a dim speck of light on a dark, moonless night.

As the moon makes it monthly rounds, the moon more often than not swings to the north or south of the planets. This month, however, the moon actually occults – goes directly in front of – Mars as seen from much of South America on the night of September 5-6, 2020. From North America, we’ll see the moon swing south of (or below) Mars; and from southern South America, folks will see the moon passing to the north of (and also below) Mars.worldwide map of the occultation of Mars.

Worldwide map of the lunar occultation of Mars on the night of September 5-6, 2020. The area in between the solid white sees the occultation in a nighttime sky, and the swath in between the dotted red lines has the occultation taking place in a daytime sky. Map via IOTA.

The occultation times are given at this IOTA (Internationa Occultation Timing Association) page in Universal Time (UTC), which you must covert to your local clock time. We give the occultation times in local time for Rio de Janeiro, Brazil (UTC-3 hours), and La Paz, Bolivia (UTC-4 hours):

Rio de Janeiro, Brazil
Occultation begins (Mars disappears behind the moon’s illuminated side): 12:15:33 a.m. local time September 6
Occulation ends (Mars reappears from behind the moon’s nighttime side): 12:35:28 a.m. local time September 6

La Paz, Bolivia
Occultation begins (Mars disappears behind the moon’s illuminated side): 10:29:23 p.m. local time September 5
Occulation ends (Mars reappears from behind the moon’s nighttime side): 11:40:41 p.m. local time September 5

Occultation times in Universal Time via IOTA

South American time zones – current time

Mars is now the 5th-brightest celestial object to light up the sky, after the sun, moon, and the planets Venus and Jupiter, respectively. However, Mars is brightening by the day, and by late September, will match Jupiter in brilliance. When Mars shines at its brightest best for the year in mid-October 2020, it’ll be some 1 1/3 times brighter than Jupiter. October 2020 showcases Mars at its best and brightest for the year, as the red planet is soon to enjoy its month-long reign as the 4th-brightest celestial object.

These next several nights – September 4, 5 and 6, 2020 – let the moon introduce you to the red planet Mars. Next month, in October 2020, Mars will supplant Jupiter as the sky’s 4th-brightest heavenly body.

Moon, Aldebaran, Pleiades before bedtime

Posted by Bruce McClure in TONIGHT | September 7, 2020

Late at night on September 7 and 8, 2020, watch as the waning gibbous moon sweeps in front of the constellation Taurus the Bull. You’ll be looking around midnight, or afterwards, or – if you’re not one to stay up late – get up before daybreak to view the moon and Taurus higher up in the sky on the mornings of September 8 or 9. The bright moon might make it tough to see the starlit figure of the Bull on these nights. But you should be able to make out Aldebaran, Taurus’ brightest star, as well as the tiny, misty, dipper-shaped Pleiades star cluster.

Then, when the moon moves away, look for the V-shaped Face of the Bull itself. The bright star Aldebaran marks one tip of the V.

Taurus is a far-northern constellation of the zodiac. That fact causes these stars to rise at an earlier hour in the Northern Hemisphere than in the Southern Hemisphere. The farther north you live, the earlier Taurus climbs above your northeast horizon. The farther south you live, the later Taurus comes up.

Want to see your specific sky view? Try Stellarium online

Or visit Sunrise Sunset Calendars, being sure to check the moonrise and moonset box, to find out when the moon rises into your sky.

View at EarthSky Community Photos. | Our friend Dr Ski in the Philippines caught the moon and Pleiades (the little cluster in the moon’s glare, at around 8 o’clock) on the morning of September 20, 2019, when they were in conjunction (same right ascension on the celestial sphere). You can also see Aldebaran here, the bright red star at about 5 o’clock. And a lunar halo! Dr Ski wrote: “I captured this image to check the field of view on my 40mm portrait lens. It’s 44° ?.” Thanks, Dr Ski!

When the moon travels in front of Taurus (or any constellation of the zodiac, for that matter), the moon can travel anywhere from 5 degrees north to 5 degrees south of the ecliptic.

A little over two years ago – on September 3, 2018 – the moon occulted (passed in front of) Aldebaran, presenting the final occultation of a monthly occultation series that started on January 29, 2015. But month by month, for the next few years, the moon’s trajectory will carry the moon farther north of Aldebaran yet closer to Alcyone, the Pleiades’ brightest star.

Then the monthly occultation series involving the moon and the Pleiades star Alcyone will begin on September 5, 2023, and conclude on July 7, 2029.Sky diagram with arrow pointing from Orion to Aldebaran and the Pleiades.

When the moon moves away, try this. The 3 stars of Orion’s Belt always point to the star Aldebaran and the Pleiades star cluster. Image via Janne/Flickr.

For the Skidi Pawnee in the American Great Plains (Nebraska), the Pleiades cluster served as an important calendar marker. When they saw the Pleiades cluster through the smoke holes of their lodges just before dawn, they knew it was time to harvest the crops.Antique etching of fierce bull with curved horns and stars shown.

Taurus the Bull via Urania’s Mirror/© Ian Ridpath.

The ecliptic – the sun’s yearly path through the constellations of the Zodiac – passes through the constellation Taurus the Bull, to the north of the star Aldebaran and to the south of the Pleiades star cluster. The sun shines in front of Taurus from about May 14 to June 21, every year.

Bottom line: Are you a night owl? Before bedtime on September 7 and 8, 2020, look eastward for the moon, which shines in front of the constellation Taurus the Bull. If you’re an early bird, look for the moon and the constellation Taurus before daybreak on September 8 and 9, 2020.

Use Big Dipper to find North Star

Posted by Larry Sessions in TONIGHT | September 9, 2020

Tonight’s chart shows Polaris and the Big and Little Dippers for a September evening. You can use the Big Dipper to find Polaris, which is also known as the North Star. Notice that a line from the two outermost stars in the bowl of the Big Dipper points to Polaris. And notice that Polaris marks the tip of the handle of the Little Dipper.

The northern sky is a large clock, with Polaris at its center. The hour hand is a line drawn through Dubhe and Merak, the two pointer stars of the Big Dipper. Because the stars make a full circle in 23 hours 56 minutes instead of exactly 24 hours, this star clock is not exactly the same as the one on the wall, but with a little practice you can learn to read it well.

View larger. | Keith Breazeal’s photo of a meteor streaking past the Big Dipper during the 2015 Perseid meteor shower. Captured at the Bear River Dam in the California Sierra Nevada mountains. Can you find Polaris in this photo?

The Big Dipper swings full circle – 360 degrees – around Polaris in about 23 hours and 56 minutes. In 24 hours, the Big Dipper actually swings more than a full circle, or 361 degrees. Does that make a difference? Yes! It means that – if you look at the same time each evening – the Big Dipper will appear just a little bit lower in the northwestern evening sky.

If you’re in the northern U.S., Canada or at a similar latitude, the Big Dipper is circumpolar for you – always above the horizon. Image via burro.astr.cwru.edu

A month from now at mid-evening, the Big Dipper will be noticeably lower in the northwest. It’ll be actually beneath the horizon as seen from the southern latitudes in the United States – although it’s circumpolar, or always above the northern horizon, as seen from the northern U.S., Canada and similarly northern latitudes.

The constant motion from night to night of these stars circling Polaris is a bit like a bear circling its prey, looking for a way to attack. Several ancient cultures from the Greeks and Romans to the Mi?kmaq Indians likened these stars to a bear.

In Greek mythology, the Big Dipper asterism represents the hindquarters and tail of the constellation Ursa Major, the Great Bear. The Mi?kmaq saw the three stars of the Big Dipper handle as hunters chasing the bear.

Watch the Big and Little Dippers circle around Polaris tonight!

Bottom line: To locate Polaris, the North Star, just draw a line between the two outer stars in the bowl of the Big Dipper.

Every visible star is within Milky Way

Posted by Deborah Byrd in TONIGHT | September 10, 2020

The image at top, showing a campfire under the Milky Way, is by Ben Coffman Photography in Oregon. He wrote:

These good folks – co-workers from one of the resorts on Mt. Hood, if I remember correctly – let me take their photo on the beach near Cape Kiwanda [a state natural area near in Pacific City, Oregon]. They looked like they were having fun.

And so they do. What could be better than a beautiful night under the Milky Way? But did you know that every night of your life is a night under the Milky Way? By that we mean … every individual star you can see with the unaided eye, in all parts of the sky, lies within the confines of our Milky Way galaxy.

Our galaxy – seen in Ben’s photo above as a bright and hazy band of stars – is estimated to be some 100,000 light-years wide and only about 1,000 light-years thick. That’s why the starlit band of the Milky Way, which is still visible in the evening this month but will soon be less so, appears so well-defined in our sky.

Gazing into it, we’re really looking edgewise into the thin plane of our own galaxy:

This image is mosaic of multiple shots on large-format film. It comprises all 360 degrees of the galaxy from our earthly vantage point. Photography was done in Ft. Davis, Texas for the northern hemisphere shots and from Broken Hill, New South Wales, Australia, for the southern portions. Note the dust lanes, which obscure our view of some features beyond them. Image via Digital Sky LLC

In the image directly above – comprising all 360 degrees of the galaxy as seen from our earthly vantage point – note that the galaxy is brightest at its center, where most of the stars and a 4-million-solar-mass black hole reside. This image shows stars down to 11th magnitude – fainter than the eye alone can see.

If you’re standing under a clear, dark night sky, you’ll see the Milky Way clearly as a band of stars stretched across the sky on late summer evenings.

The band of the Milky Way is tough to see unless you’re far from the artificial lights of the city and you’re looking on a night when the moon is down.

If you do look in a dark country sky, you’ll easily spot the Milky Way. And, assuming you’re looking from the Northern Hemisphere, you’ll notice that it gets broader and richer in the southern part of the sky, in the direction of the constellations Scorpius and Sagittarius. This is the direction toward the galaxy’s center.

If you’re in the Southern Hemisphere, the galactic center is still in the direction of Sagittarius. But from the southern part of Earth’s globe, this constellation is closer to overhead.

Bottom line: If you look in a dark country sky, you’ll easily spot the starlit band of our huge, flat Milky Way galaxy. Every star in our night sky that’s visible to the unaided eye lies inside this galaxy.

Neptune opposite sun September 11

Posted by Bruce McClure in TONIGHT | September 11, 2020

Neptune at opposition in the constellation Aquarius.

On September 11, 2020, Neptune reaches opposition, when it is 180 degrees from the sun in our sky. In other words, Earth passes more or less between Neptune and the sun, as we do every year in our yearly orbit. Also, on September 11, Earth and Neptune are closest together for the year.

By closest, we don’t mean close. Neptune, the eighth planet outward from the sun, lodges in the outskirts of our solar system. Its current distance is about approximately 2.7 billion miles (4.3 billion km).

Visit Heavens-above to know Neptune’s present distance in astronomical units.

For any superior planet – that is, for any solar system planet beyond Earth’s orbit – opposition is a special event. When any planet outside of Earth’s orbit is at or near opposition, Earth comes closest to that planet for the year, and that planet, in turn, shines most brightly in our sky. Even at opposition, however, Neptune, the eighth planet, is not bright. In fact, Neptune is the only major solar system planet that’s absolutely not visible to the unaided eye. This world is about five times fainter than the dimmest star that you can see on an inky black night. You’ll need binoculars (at least) and a detailed sky chart to see Neptune in front of the constellation Aquarius.

Visit Sky & Telescope for a detailed chart of Neptune’s position during the May 2019-March 2020 viewing season

Here’s another detailed sky chart showing Neptune

In 1989, NASA’s Voyager 2 became the first spacecraft to observe Neptune. More images from Voyager.

Because we’re more or less between Neptune and the sun around now, Neptune is rising in the east around the time of sunset, climbing highest up for the night around midnight and setting in the west around sunrise. As viewed from Earth now, this world is in front of the constellation Aquarius the Water Carrier, right next to the 4th-magnitude star Phi Aquarii.

Phi Aquarii, though faint, is easily visible to the eye alone on a dark night. Because the moon is now a waning crescent, the moon-free evening hours offer a dark sky for viewing Neptune.

Neptune and Phi Aquarii are so close together on the sky’s dome at present that the two readily fit within a single binocular field. In fact, you might see them together in a low-powered telescope, with blue-green Neptune offering a color contrast to the ruddy tint of Phi Aquarii. Neptune is nearly 30 times fainter than the star Phi Aquarii. You may well be able to view Neptune with this star tonight.

Even with an optical aid, Neptune may look like a faint star. You need to magnify Neptune by about 200 times and have a steady night of seeing to view this distant world as a small disk.Star chart, stars black on white, showing constellation Aquarius and ecliptic.

Sky chart of the constellation Aquarius via IAU. Seek for Neptune near the star Phi Aquarii.

We know it’s unlikely you’ll see Neptune unless you have optical aid and a detailed star chart via Sky & Telescope.

By the way, if Earth and Neptune both orbited the sun in perfect circles and on the same plane, then Neptune would be closest to Earth right at opposition. Yet, the Earth actually comes closest to Neptune some 19 hours before Neptune’s opposition. That’s because, at opposition, the Earth is a bit closer to the sun (and, therefore, farther from Neptune) than the Earth was 19 hours before opposition. Neptune is also closer to the sun at opposition than 19 hours before. But Earth’s change in distance is much more significant than that of Neptune.

Bottom line: Neptune’s opposition – when it’s 180 degrees from the sun on the sky’s dome – comes on September 11, 2020. You need optical aid to spot it. Links to charts here.

Moon, Venus adorn morning sky

Posted by Bruce McClure in TONIGHT | September 12, 2020

Moon and Venus adorn eastern sky before sunrise September 13, 14 and 15, 2020.

These next several days – September 13, 14 and 15, 2020 – look for the waning crescent moon and the dazzling planet Venus to adorn the eastern predawn/dawn sky. Moreover, if you have good vision, you might even be able to view these bright beauties after sunrise, or in daytime sky. After all, the moon and Venus rank as the 2nd-brightest and 3rd-brightest heavenly bodies to light up the heavens, after the sun.Waning crescent moon and star Regulus below Venus on morning of September 15, 2020.

It’ll be easy to catch Venus on September 15! For a challenge, try your luck at spotting Regulus, the brightest star to light up the constellation Leo the Lion. Binoculars might be helpful.

Venus, like Earth’s moon, displays the full range of phases in Earth’s sky, though you need a telescope to observe Venus’ changing phases. Given that the moon and Venus are nearly at the place on the sky’s dome on September 14, you might expect the moon and Venus to display a similar phase.

From North America, the waning crescent moon will be about 12 percent illuminated by sunlight on the morning of September 14. To know more specifically how much of the lunar disk is illuminated right now or at a given time, check out Heavens-Above or The Moon Tonight.

Venus, on the other hand, is exhibiting a waxing gibbous phase, with its disk 65 percent illuminated by sunshine on September 14, 2020. To know how much of the Venusian disk is illuminated by sunshine, click on Astropixels and look under the column: Phase illumination.

Moon’s orbit around Earth, seen from above. The moon’s dark side faces Earth at new moon, and its illuminated side faces Earth at full moon. At the quarter moons, we see one-half of the moon’s daytime side and one-half of its nighttime side. Read more: Understanding moon phases

The phases of the moon and Venus are so wildly different in Earth’s sky because Venus orbits the sun while the moon orbits Earth. It takes our moon about 29.5 Earth-days to complete its cycle of phases (new moon to new moon, or full moon to full moon), whereas it takes Venus about 1.6 Earth-years to complete its cycle of phases (new Venus to new Venus, or full Venus to full Venus).Diagram showing the phases of Venus at inferior and superior conjunction.

Venus is at full phase at superior conjunction and at new phase at inferior conjunction. The cycle of Venus’ phases happens over a period of 584 Earth-days (1.6 Earth-years). Image via UCLA.

Venus rises sooner before before the sun at northerly latitudes than at southerly latitudes. We give you Venus’ approximate rising time for the next several days for 60 degrees north, 40 degrees north, equator (0 degrees), and 35 degrees south:

60 degrees north latitude
Venus rises 4 2/3 hours before the sun

40 degrees north latitude
Venus rises 3 1/2 hours before the sun

Equator (0 degrees latitude)
Venus rises 2 3/4 hours before the sun

35 degrees south latitude
Venus rises 2 hours before the sun.

Hazy light pyramid in east? False dawn

Posted by Deborah Byrd in TONIGHT | September 14, 2020

The image at top is zodiacal light before dawn, as captured by Jeff Dai.

For the Northern Hemisphere, late summer/early autumn presents the best time of the year to catch the zodiacal light, or “false dawn.” And the next few days are great, because the moon will be in a waning crescent. There might be some great photo opportunities with a waning crescent moon, the dazzling planet Venus and the zodiacal light, since all will be located in the east before dawn breaks. On September 17, the moon will be new, or between the Earth and sun, and then the moon will be back entirely in the evening sky … gone from the sky before dawn, leaving it dark for your zodiacal light viewing pleasure.

Southern Hemisphere? Watch for the zodiacal light in the west, beginning about an hour after the sun goes down.

From temperate latitudes in either hemisphere, the zodiacal light is most easily seen around the time of the equinoxes. The morning zodiacal light prevails around the the time of the autumn equinox (now for the Northern Hemisphere, March-April for the Southern Hemisphere), and the evening zodiacal light around the time of the spring equinox (now for the Southern Hemisphere).

This light can be noticeable and easy to see from latitudes relatively close to Earth’s equator, for example, like those in the southern U.S. I’ve seen it many times from the latitude of southern Texas, sometimes while driving a lonely highway far from city lights, in the hour or so before true dawn begins to light the sky. In this case, the zodiacal light can resemble the lights of a city or town just over the horizon.

Meanwhile, skywatchers in the northern U.S. or Canada sometimes say, wistfully, that they’ve never seen it, although in recent years we’ve seen many photographs of the zodiacal light taken from those northerly latitudes.

Here’s the zodiacal light as captured on film in Canada. This wonderful capture is from Robert Ede in Invermere, British Columbia.zodiacal light

You need a dark sky location to see the zodiacal light, someplace where city lights aren’t obscuring the natural lights in the sky. The zodiacal light is a pyramid-shaped glow in the east before dawn (or after twilight ends in the evening, if you’re in the Southern Hemisphere now). It’s even “milkier” in appearance than the starlit trail of the summer Milky Way.

It’s most visible before dawn at this time of year because, as seen from the Northern Hemisphere, the ecliptic – or path of the sun, moon and planets – stands nearly straight up with respect to the eastern horizon before dawn now. As seen from the Southern Hemisphere, the same is true of the western horizon after true darkness falls.

The zodiacal light can be seen for up to an hour before true dawn begins to break. Look for it about 120 to 80 minutes before sunrise. Unlike true dawn, though, there’s no rosy color to the zodiacal light. The reddish skies at dawn and dusk are caused by Earth’s atmosphere, and the zodiacal light originates far outside our atmosphere.

When you see the zodiacal light, you are looking edgewise into our own solar system. The zodiacal light is actually sunlight reflecting off dust particles that move in the same plane as Earth and the other planets orbiting our sun.

Zodiacal light on the morning of August 31, 2017, with Venus in its midst, captured at Mono Lake in California. Eric Barnett wrote: “I woke from sleeping in the car thinking sunrise was coming. My photographer friend, Paul Rutigliano, said it was the zodiacal light. I jumped up, got my camera into position and captured about a dozen or so shots.”

Bottom line: No matter where you are on Earth, your local autumn is the best time to see the zodiacal light before dawn. Your local spring is the best time to see it in the evening.

Close-up on Cassiopeia the Queen

Posted by EarthSky in TONIGHT | September 15, 2020

Star map of Cassiopeia the Queen.

Tonight – or any autumn evening – Cassiopeia the Queen can be found in the northeast after sunset. This constellation has the distinctive shape of a W, or M, depending on the time of night you see it. The shape of this constellation makes Cassiopeia’s stars very noticeable. Look for the Queen, starting at nightfall or early evening.

Cassiopeia represents an ancient queen of Ethiopia. The entire constellation is sometimes also called Cassiopeia’s Chair, and some old star maps depict the queen sitting on the chair, marked by the five brightest stars of this constellation. These stars are Schedar, Caph, Gamma Cassiopeiae, Ruchbah and Segin.

The Big Dipper and the W-shaped constellation Cassiopeia circle around Polaris, the North Star, in a period of 23 hours and 56 minutes. The Big Dipper is circumpolar at 41 degrees north latitude, and all latitudes farther north.

If you have a dark sky, you can look below Cassiopeia in the northeast on these autumn evenings for a famous binocular object. This object is called the Double Cluster in Perseus. These are open star clusters, each of which consists of young stars still moving together from the primordial cloud of gas and dust that gave birth to the cluster’s stars. These clusters are familiarly known to stargazers as H and Chi Persei.

Stargazers smile when they peer at them through their binoculars, not only because they are beautiful, but also because of their names. They are named from two different alphabets, the Greek and the Roman. Stars have Greek letter names, but most star clusters don’t. Johann Bayer (1572-1625) gave Chi Persei – the cluster on the top – its Greek letter name. Then, it’s said, he ran out of Greek letters. That’s when he used a Roman letter – the letter H – to name the other cluster.

After midnight, Cassiopeia swings above Polaris, the North Star. Before dawn, she is found in the northwest. But during the evening hours, Queen Cassiopeia lights up the northeast sky.

Bottom line: The constellation Cassiopeia the Queen has the distinct shape of a W or M. Find her in the north-northeast sky on September and October evenings.

Tonight, find the Andromeda galaxy

Posted by Deborah Byrd in TONIGHT | September 16, 2020

Tonight, since the moon is waning and gone from the sky in early evening, find the Andromeda galaxy, the great spiral galaxy next door to our Milky Way. It’s the most distant thing you can see with your eye alone. It’s best seen in the evening at this time of year, assuming you’re in the Northern Hemisphere. Most people find the galaxy by star-hopping from the constellation Cassiopeia, which is a very noticeable M- or W-shaped pattern on the sky’s dome. I learned to find the Andromeda galaxy by star-hopping from the Great Square of Pegasus, to the two graceful streams of stars making up the constellation Andromeda.

Look at the chart at the top of this post. It shows both constellations – Cassiopeia and Andromeda – so you can see the galaxy’s location with respect to both. Notice the star Schedar in Cassiopeia. It’s the constellation’s brightest star, and it points to the galaxy.

Draw an imaginary line from the star Kappa Cassiopeiae (abbreviated Kappa) through the star Schedar, then go about 3 times the Kappa-Schedar distance to locate the Andromeda galaxy (Messier 31). For another view, click here .

Now let’s take a closer look at the other way to find this galaxy:Star chart with Great Square and Andromeda constellations and Andromeda galaxy marked.

Use the Great Square of Pegasus to find the Andromeda galaxy. Here’s how to do it.

The large square pattern above is the Great Square in the constellation Pegasus. The constellation Andromeda can be seen as two streams of stars extending from one side of the Square, beginning at the star Alpheratz.

Notice Mirach, then Mu Andromedae. An imaginary line drawn through these two stars points to the Andromeda galaxy.

Just be aware – bright moonlight or city lights can overwhelm the faint glow of this object. The single most important thing you need to see the galaxy is a very dark sky.

What does the galaxy look like to the eye? Assuming you have a dark sky, it appears as a large fuzzy patch – bigger than a full moon in the sky – but vastly fainter and more subtle.

View larger. | The Andromeda galaxy (upper right of photo) as seen by EarthSky Facebook friend Ted Van at a Montana campsite in mid-August. Thank you, Ted!

For binocular astronomers: Binoculars, as always, enhance the view. Binoculars are an excellent choice for beginners to observe the Andromeda galaxy, because they are so easy to point. As you stand beneath a dark sky, locate the galaxy with your eye first, then slowly bring the binoculars up to your eyes so that the galaxy comes into binocular view. If that doesn’t work for you, try sweeping the area with your binoculars. Go slowly, and be sure your eyes are dark-adapted. The galaxy will appear as a fuzzy patch to the eye. It’ll appear brighter in binoculars. Can you see that its central region is more concentrated?

With the eye, or with binoculars, or even with a backyard telescope, the Andromeda galaxy won’t look like the image below. But it will be beautiful. It’ll take your breath away.

Image of the Andromeda galaxy captured by NASA’s Wide-field Infrared Survey Explorer. Image via NASA/JPL-Caltech/UCLA

One of you wrote:

I’ve heard that the Andromeda galaxy will someday collide with our galaxy! Is that still a definite possibility?

Definite possibility describes much of what we know – or think we know – about the universe. As for the Andromeda galaxy and its future collision with our Milky Way: the first attempt to measure the radial velocity of this galaxy (its motion forward or back, along our line of sight) was made in 1912. After that, astronomers believed for some decades that the galaxy was approaching at nearly 200 miles per second (300 km/s), but later astronomers disagreed.

Then in May 2012, NASA astronomers announced they can now predict the time of this collision of titan galaxies with certainty. Remember, though, that the Andromeda Galaxy is 2.2 million light-years away, with a single light-year being almost 10 trillion kilometers (6 trillion miles). So although it does appear that this galaxy is approaching our Milky Way galaxy … it’s nothing to lose sleep over. When will they collide? According to NASA astronomers in 2012, it’ll be four billion years from now.

Read more: Will the Milky Way and Andromeda galaxies collide someday?

Plus when galaxies collide, they don’t exactly destroy each other. Because there’s so much more space than stars in our universe, colliding galaxies pass through each other, like ghosts.

But colliding galaxies do interact. Check out this cool video: Night sky as Milky Way and Andromeda galaxies merge.

Bottom line: The Andromeda galaxy, aka M31, will be visible on dark, moonless evenings from now until the beginning of spring. This post tells you how to use the constellations Cassiopeia and Pegasus to find it. Be sure you’re looking on a moonless night, far from city lights. This galaxy is approaching our Milky Way galaxy, across the vastness of space. Astronomers say that – four billion years from now – our two galaxies will collide.

Use Great Square to find Andromeda galaxy

Posted by Bruce McClure in TONIGHT | September 17, 2020

Tonight, find the large spiral galaxy next door. As shown on the chart at the top of this post, the Great Square of Pegasus serves as a great jumping off point for finding the Andromeda galaxy, otherwise known as M31. The Great Square sparkles over your eastern horizon at nightfall and travels westward across the sky throughout the night. For some idea of the Great Square’s size, extend your hand an arm’s length from your eye. You’ll see that any two Great Square stars are farther apart than the width of your hand.

As seen from mid-northern latitudes, the Square of Pegasus looks like a baseball diamond whenever it resides in the eastern sky. Imagine the farthest star to the left – Alpheratz – as the third-base star. An imaginary line drawn from the first-base star through Alpheratz points in the general direction of the Andromeda galaxy.

The Andromeda galaxy and two satellite galaxies as seen through a powerful telescope. To the eye, the galaxy looks like a fuzzy patch. It’s an island of stars in space, much like our Milky Way. Image Credit: NOAO

If it’s dark enough, you’ll see two streamers of stars flying to the north (or left) of the star Alpheratz. To some people, this grouping of stars looks like a bugle or a cornucopia. Along the bottom streamer, star-hop from Alpheratz to the star Mirach. Draw an imaginary line from Mirach through the upper streamer star (Mu Andromedae), and go twice the distance. You’ve just located the Andromeda galaxy!

If you can’t see this fuzzy patch of light with the unaided eye, maybe your sky isn’t dark enough. Try binoculars! Or try going to darker sky.

Read more: Andromeda galaxy, closest spiral to Milky Way

View larger. | The Andromeda galaxy (right side of photo) as seen by EarthSky Facebook friend Ted Van at a Montana campsite in mid-August 2012. Thank you, Ted!

Bottom line: If you can find the Great Square of Pegasus, then you can star-hop to the Andromeda galaxy.

Young moon after sunset September 18-21

Posted by Bruce McClure in TONIGHT | September 18, 2020

Young moon low in the west after sunset.

Yesterday – September 17, 2020 – the new moon passed 5 degrees north of the sun to transition out of the morning sky and into the evening sky. The moon disappears from view on the day of new moon. That’s because the moon more or less rises and sets with the sun, so it’s lost in the sun’s glare throughout the day.

After any new moon comes to pass, the moon continues to travel eastward of the sun on the sky’s dome. Lucky for us, the moon reaches perigee – the moon’s closest point to Earth in its monthly orbit – on September 18, 2020. That means the young moon is traveling away from the sun at a maximum orbital speed right now. So we’re expecting that a number of diligent observers might catch the young whisker-thin waxing crescent moon at evening dusk September 18.

To maximize your chances of spotting the young moon on September 18, find an unobstructed horizon in the direction of sunset. If you have them, bring along binoculars. Look westward, near the sunset point on the horizon, for a pale crescent some 45 minutes to one hour after sundown. Don’t dally, though! From many places worldwide, the September 18th young moon follows the sun beneath the horizon before nightfall, and won’t return to the evening sky until after sunset the following day (September 19).

For almost all the world on September 18, 2020, the moon will be more than one day (24 hours) old at sunset. Even so, it’ll take a concerted effort to catch the slender crescent. If you miss the young moon after sunset September 18, try again the next few days. Each day, a wider and brighter lunar crescent appears higher in the sky at sunset, and stays out longer after sundown.Worldwide map of day and night sides of world one day after new moon.

The day and night sides of Earth one day after new moon (2020 September 18 at 11 UTC). The shadow line at right (crossing eastern Asia) shows where the moon will be one day old at sunset. The line of sunset travels westward (leftward), so all places to the west (left) of this shadow line has an older moon at sunset. Map via EarthView.

Generally, it’s hard to spot a moon that’s less than one day old (less than 24 hours after new moon). But if there’s anyplace that might catch a young moon less than 24 hours after new moon, it’s Australia. September young moons are easier to view from the Southern Hemisphere than the Northern Hemisphere. That’s because a young moon stays out longer after sunset in late winter/early spring than in later summer/early autumn.

This young moon takes place just a few days before the Southern Hemisphere’s spring equinox and the Northern Hemisphere’s autumn equinox. At sunset on the spring equinox, the ecliptic – annual pathway of the sun, and approximate monthly pathway of the moon – hits the horizon at its steepest angle for the year. On the other hand, at sunset on the autumn equinox, the ecliptic hits the horizon at its shallowest angle for the year. Therefore, all else being equal, the Southern Hemisphere has the upper hand for catching any September young moon.

However, this time around, this moon resides somewhat north of the ecliptic. To some degree, the more northerly moon partially takes away the Southern Hemisphere’s advantage and the Northern Hemisphere’s disadvantage. Even so, the Southern Hemisphere enjoys the overall advantage for this September young moon sighting!Southern Hemisphere view of the young moon in September.

This is the view of the young moon from Valdivia, Chile (40 degrees south latitude).

The planet Mercury and the bright star Spica are in the vicinity of the young moon, but these bright lights will be lost in the afterglow of sunset at northerly latitudes. Since Mercury and Spica lodge to the south of the ecliptic, they’re much easier to view from the Southern Hemisphere. We contrast Philadelphia, Pennsylvania (40 degrees north Latitude), USA, with Valdivia, Chile (40 degrees south latitude), both of which resdie near the same meridian: 75 degrees west longitude.

Philadelphia, Pennsylvania
Moon sets one hour 10 minutes after the sun on September 18
Mercury sets 48 minutes after the sun on September 18
Spica sets 56 minutes after the sun on September 18

Valdivia, Chile
Moon sets one hour and 38 minutes after the sun on September 18
Mercury sets one hour and 56 minutes after the sun on September 18
Spica sets 2 two hours and 21 minutes after the sun on September 18

After sunset these next several days – September 18, 19, 20 and 21, 2020 – watch for the waxing crescent moon’s return to the western evening sky. Plus, note the earthshine softly illuminating the dark side of the moon.

Year’s fastest sunsets around equinoxes

Posted by Bruce McClure in TONIGHT | September 21, 2020

Tonight – at sunset – here’s a natural phenomenon you might never have imagined. That is, the sun actually sets faster around the time of an equinox. The fastest sunsets (and sunrises) occur at or near the equinoxes. And the slowest sunsets (and sunrises) occur at or near the solstices. This is true whether you live in the Northern or Southern Hemisphere.

And, by the way, when we say sunset here, we’re talking about the actual number of minutes it takes for the body of the sun to sink below the western horizon.Four views of Earth. Line between light and dark slanted in two views, vertical in the other two.

Equinoxes and solstices, via Geosync

Why does the sun set so quickly around the equinoxes? At every equinox, the sun pretty much rises due east and sets due west. That means – on the day of an equinox – the setting sun hits the horizon at its steepest possible angle.

Meanwhile, at a solstice, the sun is setting farthest north or farthest south of due west. The farther the sun sets from due west along the horizon, the shallower the angle of the setting sun. That means a longer duration for sunset at the solstices.

The sunset duration varies by latitude. Farther north or south on the Earth’s globe, the duration of sunset lasts longer. Closer to the equator, the duration is shorter. But let’s just consider one latitude, 40 degrees north, the latitude of Denver or Philadelphia in the United States, and Beijing in China. At that latitude, on the day of equinox, the sun sets in about 2 3/4 minutes.

On the other hand, the solstice sun sets in roughly 3 1/4 minutes at 40 degrees latitude.

The equinox is an event that takes place in Earth’s orbit around the sun.

When is the equinox? The September equinox will arrive on September 22, 2020, at 13:31 UTC. Although the equinox happens at the same moment worldwide, your clock times will depend on your time zone. For time zones in the continental U.S., this equinox comes on September 22 at 9:31 a.m. EDT, 8:31 a.m. CDT, 7:31 a.m. MDT or 6:31 a.m. PDT. Translate to your time zone.

Bottom line: The fastest sunsets of the year are happening now, around the time of the September equinox.

Equinox sun is over Earth’s equator

Posted by Bruce McClure in TONIGHT | September 22, 2020

The illustration at top by Tau’olunga via Wikimedia Commons shows the day arc of the sun, every hour – during the equinoxes – as seen on the celestial dome from the equator. Also showing twilight suns down to -18 degrees latitude. Note the sun is at the zenith at noon and that the tree’s shadow is cast straight down. That is – as seen from the equator on the day of an equinox – a tree stands in the center of its own shadow.

The 2020 autumnal equinox for the Northern Hemisphere (spring equinox for the Southern Hemisphere) happens on Tuesday, September 22, at 13:31 UTC. At this special moment – the instant of the September equinox – the sun is at zenith, or straight overhead, as seen from Earth’s equator.

That’s the meaning of an equinox. The September equinox sun crosses the sky’s equator, going from north to south.

Although the equinox happens at the same instant for everyone worldwide, the clock time for the equinox varies by time zone. In the U.S., the local clock time for the September equinox will be Tuesday, September 22, at 9:31 a.m. EDT, 8:31 a.m. CDT, 7:31 a.m. MDT and 6:31 a.m. PDT.

On the day of the equinox, the sun pretty much rises due east and sets due west all over the world, with everyone worldwide receiving approximately equal portions of day and night.

When October comes rolling around, that’ll change dramatically. By then, the sun will rise noticeably south of due east and will set noticeably south of due west. That’ll mean shorter days and longer nights for the Northern Hemisphere, and longer days and shorter nights in the Southern Hemisphere.

After the equinox, the sun (and migrating birds) will continue to travel southward to the southern climes. Arctic sea ice will begin to freeze; Antarctic ice will start melting. The great wheel of the seasons will continue to turn.

How to celebrate?

Try to watch as the sun rises due east and sets due west on the day of the equinox. If you do that from your backyard, or deck, or a local park – somewhere that you have familiar landmarks – you’ll gain a handy tool for astronomy: that is, the tool of knowing the direction of due east.

Bottom line: Around the equinox, the sun is overhead at noon for people at Earth’s equator.

Moon, Jupiter, Saturn September 23-26

Posted by Bruce McClure in TONIGHT | September 23, 2020

The moon goes by the planets Jupiter and Saturn in the September 2020 evening sky.

These next several evenings – September 23, 24, 25 and 26, 2020 – feature the moon and the solar system’s two largest gas giant planets, Jupiter and Saturn. Given clear skies, you can’t miss the moon and Jupiter. The moon is the second-brightest celestial object, after the sun; Jupiter ranks as the fourth-brightest, after the planet Venus, which is a fixture of the morning sky. With Venus gone from the evening sky, there’s no way to mistake Venus for Jupiter in September 2020. Jupiter is simply the brightest starlike object visible.

As viewed from the mainland United States, the moon reaches its first quarter phase on September 23, 2020, at 9:55 p.m. EDT, 8:55 p.m. CDT, 7:55 p.m. MDT and 6:55 p.m. PDT. By Universal Time (UTC), the moon reaches its first quarter phase on September 24, 2020, at 1:55 UTC. At first quarter, the one half of the moon is illuminated in sunshine while the dark half is engulfed in the moon’s own shadow.

The relative sizes of the solar system planets via NASA. Distances are NOT to scale. Mercury and Venus are called inferior planets because they orbit the sun inside of Earth’s orbit. The superior planets – planets orbiting the sun outside of Earth’s orbit – are Mars, Jupiter, Saturn, Uranus and Neptune. Jupiter and Saturn are referred to as gas giants whereas Uranus and Neptune are often called ice giants.

The dark side of a waxing moon always points eastward (direction of sunrise). And the moon in its orbit always travels toward the east, too, relative to the sky background. The moon travels about 1/2 degree eastward – its own width on our sky’s dome – every hour. So, in the days ahead, the moon will go past Jupiter, and then it’ll go by Saturn.

The moon will swing 1.6 degrees to the south of Jupiter on September 25, 2020, at 6:46 UTC. Then the moon will sweep 2.3 degrees to the south of Saturn on September 25, 2020, at 20:46 UTC. When an almanac gives the degree measure between the moon and a given planet, it means as viewed from the center of the Earth (not the Earth’s surface). Because the moon is close enough to Earth to display a parallax, the angular separation between the moon and planet can vary somewhat around the world.

A telescope, even a modest backyard variety, works like a charm for viewing the moon, Jupiter and Saturn. Dust off that telescope and zoom in to scan the lunar terrain, the four major moons of Jupiter and Saturn’s rings.

Take a gander at the moon along the lunar terminator – the shadow line that divides the lunar day from the lunar night. The long shadows along the terminator provide a wondrous three-dimensional portrayal of the lunar mountains, craters and valleys. Believe it or not, this is one time that a dark sky is not an advantage. The glare of the moon is too overwhelming at nighttime, so enjoy your moon watching adventure in a twilight or daytime sky.

Jupiter’s four major moons – Io, Europa, Ganymede and Callisto – are quite easy to see in a low-powered telescope, usually appearing as pinpoints of light along the same plane. Sometimes, a moon or two might not be visible, because these Jovian moons regularly pass behind and in front of Jupiter.Large fuzzy white dot with tiny bright dots to left and right.

Jupiter and its moons as seen through a telescope on August 15, 2009. Visit Sky & Telescope’s Jupiter moon calculator for the present position of Jupiter’s four major moons.

Click here to find out the positions of these Galilean moons for right now or some chosen time, via Sky and Telescope.

Last but hardly least, aim your telescope at Saturn to see this planet’s glorious rings, which circle Saturn above this planet’s equator. Fortunately, Saturn’s rings are inclined at around 21 degrees in Earth’s sky, so they are quite easy to see in 2020. There are years (2009, 2025) when Saturn’s rings are not inclined at all, but appear edge-on in Earth’s sky. At those times, the rings become invisible. But not this year, because we enjoy a favorable inclination of the rings in 2020.

These images suggest how the ringed planet Saturn might look when seen through a telescope with an aperture 4 inches (100 mm) in diameter (top) and through a larger instrument with an 8-inch aperture (bottom). Image via SkyandTelescope.com/NASA/Hubble Space Telescope.

Best of all, we can enjoy observing the lunar landscape, Jupiter’s moons and Saturn’s rings in a sky that’s beset with moonlight or light pollution. These solar system wonders don’t demand the dark sky that far-off galaxies and nebula do.

Bottom line: On September 23, 24, 25 and 26, 2020, use the moon to find the planets Jupiter and Saturn. Have a telescope? Then use it to view Jupiter’s four major moons and Saturn’s glorious rings.

Mercury in the west after sunset

Posted by Bruce McClure in TONIGHT | September 26, 2020

View of Mercury from the Southern Hemisphere.

Starting on September 26, 2020, Mercury – the innermost planet – swings out to an elongation of over 25 degrees east of the sun, placing Mercury in the western sky after sunset. Moreover, Mercury remains at better than 25 degrees east of the sun until October 7, 2020. On October 1, 2020 – on the same date as the full moon – Mercury sweeps to its greatest elongation of 25.8 degrees east of the sun.

When a greatest evening elongation of an inferior planet, such as Mercury, closely coincides with the spring equinox, we can anticipate on a fine evening apparition of Mercury. Since the recent September equinox counts as the Southern Hemisphere’s spring equinox, the Southern Hemisphere can expect a favorable evening view of Mercury during the next couple of weeks.Northern Hemisphere view of Mercury in evening sky.

The shallow tilt of the ecliptic at mid-northern latitudes submerges the planet Mercury and the star Spica in the afterglow of sunset. See the feature chart at top for temperate latitudes in the Southern Hemisphere.

Yet, when a greatest evening elongation of Mercury closely coincides with the autumn equinox, it results in a poor apparition of Mercury in the evening sky. Given that the September equinox is the Northern Hemisphere’s autumn equinox, mid-northern latitudes will have a hard time teasing Mercury out of the afterglow of sunset, even with binoculars.

In short, Mercury sets closer to sunset at more northerly latitudes, but stays out longer after sunset at more southerly latitudes. We give Mercury’s setting time relative to sunset, and the time for nightfall (end of astronomical twilight).

For October 1, 2020:

40 degrees north latitude
Mercury sets 50 minutes (5/6 hour) after sunset
Nightfall: 90 minutes (1 1/2 hours) after sunset

Equator (0 degrees latitude)
Mercury sets 90 minutes (1 1/2 hours) after sunset
Nightfall: 70 minutes (1 1/6 hours) after sunset

35 degrees south latitude
Mercury sets over 120 minutes (2 hours) after sunset
Nightfall: 86 minutes (nearly 1 1/2 hours) after sunset

Want more specific info? Click here for a sky almanac

In either the Northern or Southern Hemisphere, a greatest eastern (evening) elongation of an inferior planet (Mercury or Venus) is most favorable when it coincides with the spring equinox, and the least so when a greatest evening elongation coincides with the autumn equinox. That’s because the ecliptic – the pathway of the planets – hits the horizon at its steepest angle for the year at sunset on the spring equinox, yet at its shallowest angle for the year at sunset on the autumn equinox. Hence, the Southern Hemisphere enjoys a ringside seat to this present evening apparition of Mercury whereas northerly latitudes must be relegated to the bleachers.

At sunset on the spring equinox, the ecliptic – pathway of the sun. moon and planets – hits the sunset horizon at its steepest angle of the year. But at sunset on the autumn equinox, the ecliptic hits the sunset horizon at its shallowest angle. Therefore, when an inferior planet at its greatest evening elongation coincides closely with the spring equinox, it stays out for a maximum time after sunset. Image via Dominick Ford.

Strictly speaking, the ecliptic is the Earth’s orbital plane projected onto the constellations of the zodiac. The ecliptic also depicts the sun’s annual eastward path in front of the backdrop stars, as viewed from Earth. (However, the sun’s apparent annual motion is really a reflection of Earth orbiting the sun.) Because the planets orbit the sun on the nearly the same planet that Earth orbits the sun, you’ll always find the planets of the solar system on or near the ecliptic.

If you live in the Southern Hemisphere, take advantage of your golden opportunity to view Mercury in the evening sky during the last week of September and first week of October.

Moon, Jupiter, Saturn August 27 to 29

Posted by Bruce McClure in TONIGHT | 1 day ago

Moon goes by the bright planets Jupiter and Saturn on August 27, 28 and 29, 2020.

These next several evenings – August 27, 28 and 29, 2020 – watch for the waxing gibbous moon to pass by the two biggest planets in our solar system, Jupiter and Saturn. Both worlds are gas giants. Jupiter is bigger and by far the brighter planet, shining some eight times more brilliantly than Saturn. Yet the famous planet of the rings shines as brightly as the brightest stars. Just look up on these nights! You can’t miss these bright worlds near the moon.

And notice how close together in the sky these two planets are. That’s because they’re headed for a great conjunction later this year. If you find them in the coming evenings, you’ll enjoy watching them for the remainder of 2020.

Read more: Before 2020 ends, a great conjunction of Jupiter and Saturn

Jupiter ranks as the fourth-brightest celestial body to light up the heavens, after the sun, moon and the planet Venus. But there’s no way to mistake Venus for Jupiter, or vice versa, because – at present – Jupiter rules the evening sky while Venus is up at dawn. Around the world, in the wee hours of the morning, Jupiter sets in the southwest at roughly the same time that Venus rises in the northeast.

Meanwhile, Saturn – the most distant word that you can see easily with the unaided eye – is twice as bright as the 1st-magnitude star Antares, Heart of the Scorpion. You might have seen the moon in the vicinity of Antares a few days ago.

Live in the U.S. or Canada? Find out when Jupiter sets and Venus rises via Old Farmer’s Almanac.

For virtually anywhere worldwide, find out when Jupiter sets and Venus rises via TimeandDate.com.

Visit Heavens-Above for the moon’s present position on the zodiac.

Here’s a constellation to look for near the moon, Jupiter and Saturn in the next few days. Scorpius is one of the few constellations that looks like its namesake. The bright red star Antares marks the Scorpion’s Heart. On the night of August 27, an imaginary line drawn from Jupiter and past the moon points to Antares. Also, notice the 2 stars at the tip of the Scorpion’s Tail. These 2 stars – Shaula and Lesath – are known as The Stinger.

There are two reasons for Jupiter and Saturn’s brilliance. First of all, these planets are huge; and, secondly, they have a high albedo (reflectivity). Jupiter has 1,331 times the volume of Earth, whereas Saturn has 764 times the Earth’s volume. Jupiter reflects about 52% of the incoming sunlight, while Saturn reflects about 47%. In contrast, our moon only reflects about 12% of the incoming sunlight.

Unlike the stars, which shine by their own light, Jupiter and Saturn shine by reflecting the light of the sun. Despite Jupiter residing 4.4 astronomical units (AU) from Earth and Saturn at 9.2 AU from Earth right now, these planets still stand out in Earth’s sky. By the way, one AU = one sun/Earth distance.

Find out current planetary distances from Earth and the sun via Heavens-Above.

Saturn’s brilliance also depends the tilt of its majestic rings. You need a telescope to view the rings, but their inclination affects the planet’s brightness as seen from Earth even when looking with the eye alone. Saturn appears brightest when the rings are inclined at a maximum of 27 degrees toward Earth, and dimmest when the rings appear edge-on (0 degrees).

Presently, the rings are inclined at a little more than 21 degrees, adding to Saturn’s overall brilliance.28 pictures of Saturn with the rings tilted at different angles.

The tilt of Saturn’s rings has a great impact on its overall brightness. In years when Saturn’s rings are edge-on as seen from Earth (2009 and 2025), Saturn appears considerably dimmer than in years when Saturn’s rings are maximally titled toward Earth (2017 and 2032). This year, in 2020, Saturn’s rings are still quite inclined. Image via Wikimedia Commons.

Bottom line: On August 27, 28 and 29, 2020, use the moon to locate the two largest planets of the solar system, Jupiter and Saturn.

Mercury in the west after sunset

Posted by Bruce McClure in TONIGHT | September 26, 2020

View of Mercury from the Southern Hemisphere.

Starting on September 26, 2020, Mercury – the innermost planet – swings out to an elongation of over 25 degrees east of the sun, placing Mercury in the western sky after sunset. Moreover, Mercury remains at better than 25 degrees east of the sun until October 7, 2020. On October 1, 2020 – on the same date as the full moon – Mercury sweeps to its greatest elongation of 25.8 degrees east of the sun.

When a greatest evening elongation of an inferior planet, such as Mercury, closely coincides with the spring equinox, we can anticipate on a fine evening apparition of Mercury. Since the recent September equinox counts as the Southern Hemisphere’s spring equinox, the Southern Hemisphere can expect a favorable evening view of Mercury during the next couple of weeks.Northern Hemisphere view of Mercury in evening sky.

The shallow tilt of the ecliptic at mid-northern latitudes submerges the planet Mercury and the star Spica in the afterglow of sunset. See the feature chart at top for temperate latitudes in the Southern Hemisphere.

Yet, when a greatest evening elongation of Mercury closely coincides with the autumn equinox, it results in a poor apparition of Mercury in the evening sky. Given that the September equinox is the Northern Hemisphere’s autumn equinox, mid-northern latitudes will have a hard time teasing Mercury out of the afterglow of sunset, even with binoculars.

In short, Mercury sets closer to sunset at more northerly latitudes, but stays out longer after sunset at more southerly latitudes. We give Mercury’s setting time relative to sunset, and the time for nightfall (end of astronomical twilight).

For October 1, 2020:

40 degrees north latitude
Mercury sets 50 minutes (5/6 hour) after sunset
Nightfall: 90 minutes (1 1/2 hours) after sunset

Equator (0 degrees latitude)
Mercury sets 90 minutes (1 1/2 hours) after sunset
Nightfall: 70 minutes (1 1/6 hours) after sunset

35 degrees south latitude
Mercury sets over 120 minutes (2 hours) after sunset
Nightfall: 86 minutes (nearly 1 1/2 hours) after sunset

Want more specific info? Click here for a sky almanac

In either the Northern or Southern Hemisphere, a greatest eastern (evening) elongation of an inferior planet (Mercury or Venus) is most favorable when it coincides with the spring equinox, and the least so when a greatest evening elongation coincides with the autumn equinox. That’s because the ecliptic – the pathway of the planets – hits the horizon at its steepest angle for the year at sunset on the spring equinox, yet at its shallowest angle for the year at sunset on the autumn equinox. Hence, the Southern Hemisphere enjoys a ringside seat to this present evening apparition of Mercury whereas northerly latitudes must be relegated to the bleachers.

At sunset on the spring equinox, the ecliptic – pathway of the sun. moon and planets – hits the sunset horizon at its steepest angle of the year. But at sunset on the autumn equinox, the ecliptic hits the sunset horizon at its shallowest angle. Therefore, when an inferior planet at its greatest evening elongation coincides closely with the spring equinox, it stays out for a maximum time after sunset. Image via Dominick Ford.

Strictly speaking, the ecliptic is the Earth’s orbital plane projected onto the constellations of the zodiac. The ecliptic also depicts the sun’s annual eastward path in front of the backdrop stars, as viewed from Earth. (However, the sun’s apparent annual motion is really a reflection of Earth orbiting the sun.) Because the planets orbit the sun on the nearly the same planet that Earth orbits the sun, you’ll always find the planets of the solar system on or near the ecliptic.

If you live in the Southern Hemisphere, take advantage of your golden opportunity to view Mercury in the evening sky during the last week of September and first week of October.

Orion’s Belt points to dazzling Sirius

Posted by Deborah Byrd in TONIGHT | September 27, 2020

Sky chart of Orion and Sirius.

It’s one of the neatest tricks in all the heavens … Orion’s Belt points to Sirius in the constellation Canis Major the Greater Dog. Sirius is the brightest star in the nighttime sky. It’s up before dawn now but will be shifting into the evening sky as the months pass. Orion is found in the predawn morning sky every September.

Sirius is Dog Star and brightest star

Yes, you can find Orion. If you go outside and look south to southeast before dawn now, you’ll notice Orion’s Belt, which consists of a short, straight row of medium-bright stars. Just draw a line through Orion’s Belt and extend that line toward the horizon. You’ll easily spot Sirius, the sky’s brightest star.

Sirius is in the constellation Canis Major the Greater Dog. It’s often called the Dog Star.

Two planets (Venus and Jupiter) shine more brilliantly than Sirius, but you simply can’t mistake either planet for Sirius in the September 2019 morning sky. Venus is now lost in the sun’s glare, whereas Jupiter sets before Sirius rises. Once again, use Orion’s Belt to locate Sirius in the southeast sky.

Orion, Sirius, Venus and more as seen on August 30, 2017, by Tom Wildoner. He took the photo from the U.S. state of Pennsylvania, but these stars and Venus can be seen from around the world now, in the direction of sunrise before the sun comes up. Read more about this photo.

Moon, Fomalhaut in late September

Posted by Bruce McClure in TONIGHT | September 28, 2020

Moon swings by the star Fomalhaut in late September 2020.

These next several nights – September 28, 29 and 30 – 2020, use the bright waxing gibbous moon to find the star Fomalhaut. This 1st-magnitude star appears in a part of the sky that’s largely empty of bright stars. For this reason, Fomalhaut is often called the Lonely One or Solitary One. It should be bright enough to withstand the lunar glare in late September.

Fomalhaut lies way south of the ecliptic, which, on sky charts, depicts the sun’s annual path in front of the constellations of the zodiac. The ecliptic also depicts the approximate monthly path of the moon in front of the zodiac. From mid-northern latitudes in the Northern Hemisphere, at about 8 to 9 p.m., you’ll find Fomalhaut peeking out at you just above the southeast horizon. No other bright star sits so low in the southeast in the evening at this time of year. From this hemisphere, Fomalhaut dances close to the southern horizon until well after midnight on these autumn nights. It reaches its highest point for the night in the southern sky at about 10 to 11 p.m. local time (11 p.m. to midnight daylight saving time). At mid-northern latitudes, Fomalhaut sets in the southwest around 2 a.m. local time (3 a.m. daylight saving time).

For the fun of it, we show Neptune, the eighth (and farthest known) solar system planet, on our chart. This world is way too distant and faint to see with the unaided eye. You need an optical aid to see Neptune, and it also helps to have a moonless night.

From the Southern Hemisphere, Fomalhaut rises in a southeasterly direction, too, but this star climbs much higher up in the Southern Hemisphere sky and stays out for a much longer period of time. At southerly latitudes, this star rises earlier and sets later than it does at northerly latitudes.

Fomalhaut is a bright white star. Depending on whose list you believe, Fomalhaut is either the 17th or the 18th brightest star in the sky, and we regard Fomalhaut as the Autumn Star in the Northern Hemisphere.

Roughly translated from Arabic, Fomalhaut’s name means mouth of the fish or whale.

By the way, Fomalhaut is famous in astronomical science as the first star with a visible exoplanet. Click here for more about Fomalhaut and its planet, Fomalhaut b or Dagon

View larger. | This false-color composite image, taken with the Hubble Space Telescope, reveals the orbital motion of the planet Fomalhaut b, aka Dagon. Image via NASA/ESA/P. Kalas. Read more about Fomalhaut and Dagon.

Use the moon to locate Fomalhaut, the Autumn Star, in late September 2020.

Always Keeping look up