September Dark Sky Treats, an early evening Planet Parade, Zodiacal Light, and Comet Zinner zips through Auriga!
A Binocular Comet
This fall, astronomers are keeping an eye on two comets that are predicted to brighten enough to see with binoculars and possibly even your unaided eyes. I’m going to continue updating you about them, even though, like cats, comets have tails and are extremely prone to doing their own thing, despite what we might want them to do.
Comet 21P/Giacobini-Zinner returns to our vicinity every 6.5 years — hence the “P” for “periodic” in its designation. It has been gradually brightening because it is approaching Earth. (It will be closest to us next Monday, then it will begin to fade.) This week will be an excellent time to see it because the moon will be out of the evening sky (and waning towards its new phase). You should be able to see the faint fuzzy greenish object in binoculars or a small telescope, if you can escape city lights. A faint tail might be noted extending to the upper right of the comet (although your telescope will flip that around).
The comet is located in the northeastern sky on a track that carries it lower every night. Tonight (Sunday) it will be found about a thumb’s width (1.5°) to the right of the very bright star Capella in Auriga (the Charioteer); putting the two objects inside the field of view of a low magnification telescope. Capella will still be very low at 11 pm local time, but the comet and star will be carried higher during the course of the night due to Earth’s rotation. For the balance of this week, the comet will move away from Capella as it traverses Auriga’s roughly circular ring of stars. It will central in the constellation during mid-week.
A second comet named 46P/Wirtanen is predicted to become much brighter by December. Right now, it is tickling the belly of the whale (Cetus), but it’s far too dim to look for yet.
During moonless periods in September and October annually, the steep morning ecliptic favors the appearance of the zodiacal light in the eastern sky for about half an hour before dawn. This is reflected sunlight from interplanetary particles concentrated in the plane of the solar system. During the two weeks starting just before the new moon on September 9, look east below the stars of Cancer (the Crab) for a broad wedge of faint light rising from the horizon and centered on the ecliptic. Don’t confuse it with the Milky Way, which is sitting further to the southeast.
The Moon and Planets
When the moon rises at midnight on Sunday, September 2, it will be half illuminated — on the left (sunward) side because it will be at its Last Quarter phase. The name of this phase indicates that it has a quarter of an orbit remaining until it reaches New Moon next Sunday. Interestingly, Last Quarter moons, which always rise about midnight and set about noon, occupy the spot in the sky that Earth is travelling towards.
Tonight (Sunday), the moon will be sitting only two finger widths to the lower left of Aldebaran, the brightest star in Taurus (the Bull). The moon and bright star will cross the sky together while the moon’s eastward orbital motion will slowly draw them apart. Two hours earlier, at 9:50 pm EDT (01:50 UT), observers in Greenland and northernmost Canada will see the moon cross in front of, or occult, Aldebaran.
For the rest of this week, folks who have clear skies during the wee hours can see the waning crescent moon pass above Orion’s (the Hunter) upraised club on Tuesday morning, and through Gemini’s (the Twins) legs on Wednesday. In the eastern pre-dawn sky of Saturday, the thin old crescent moon will sit 2 fingers widths above Leo’s (the Lion) brightest star Regulus, and a palm’s width above Mercury. New Moon officially occurs at 2 pm EDT on Sunday afternoon.
For people who live in the GTA and mid-northern latitudes around the world, Mercury will be very easy to see in the eastern pre-dawn sky this week. Last Sunday, Mercury reached its widest angle west of the Sun. This week, it will still rise in the east well before the sun. You’ll be able to see it between about 5:45 and 6:15 am local time all week. Try to pick a spot with a low and uncluttered eastern horizon.
Extremely bright Venus is quickly descending the western early evening sky each evening as its orbit carries it back towards the sun. This week, it will set shortly before 9 pm local time. During the past few weeks, the bright planet has been approaching the bright star Spica in Virgo (the Maiden). The effect is caused by Earth’s motion carrying the entire sky westward faster than Venus is moving. They “kissed” on Friday and Saturday evening. The pair is still a gorgeous sight in binoculars — although Venus will now be drawing away from the star. In a small telescope, Venus’ disk will resemble a first quarter moon, half-lit on the sunward side (although your telescope might flip the view). The planet will also be growing larger in apparent diameter because it is travelling towards the Earth right now.
We are in the closing chapter for observing Jupiter this year. The earlier sunsets will buy us some extra evening observing time, but its position low in the sky will add a great deal of extra blurring atmosphere between it and our telescopes. This week, the very bright planet will emerge from the southwestern twilight soon after dusk, and then set in the west-southwest just after 10 pm local time. Jupiter, which has been slowly shifting eastwards, will continue to pull away from the nearby bright star Zubenelgenubi, the brightest star in Libra (the Scales). In binoculars, you’ll plainly see that Zubenelgenubi is a pair of stars. While you have the binoculars handy, see if you can see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) flanking the planet.
The Great Red Spot (or GRS, for short) takes about three hours to cross Jupiter’s disk. But the planet’s 10-hour rotation period (i.e., its day) means that the spot is only observable from Earth every 2–3 nights. If you’d like to see the GRS, use a medium-sized telescope (or larger). You’ll have your best luck on evenings with steady air — when the stars are not twinkling too much. Try to look within an hour before or after the following times: Wednesday, September 5 at 8:56 pm. All times are given in Eastern Daylight Time (EDT), so adjust for your local time zone.
Medium-bright and yellow-tinted Saturn will appear not too high up the darkening southern sky shortly after dusk this week. The planet will reach its highest elevation of about 2 fist diameters above the southern horizon at around 8:40 pm local time, and then descend to set in the west by about 1 am. This summer, the ringed planet has been 5 finger widths to the upper right of the “lid” star of the Teapot in Sagittarius (the Archer). As the sky darkens, even a small telescope should be able to show you some of Saturn’s larger moons, especially Titan. Using a clock’s dial analogy, Titan will move counter-clockwise this week from a position at 8 o’clock (left of the planet) to 3 o’clock (right of the planet). (Remember that your telescope might flip and/or invert the view. Use the moon to find out how your telescope changes things.)
Mars will still be very bright this week. Visually, it will appear pink or orangey due to the global dust storm it has experienced recently. Mars will appear above the southeastern horizon after dusk and then climb higher until 10:30 pm local time, when it will reach an elevation of about 20° (or two outstretched fist diameters) above the southern horizon. (That will be the best hour to view the planet in a telescope because it will then be shining through the least amount of Earth’s distorting atmosphere.) Note that 20° is lower than many trees and buildings, so a clear southern vista is essential. It will set in the west before 3 am.
At visual magnitude 5.8, blue-green coloured Uranus is visible from late evening until dawn. You can see it without optical aid under very dark skies, or in binoculars and telescopes under moderately light-polluted skies. The ice giant planet is located in the eastern sky, about 4.5 finger widths to the left of the modestly bright star Torcular (Omega Piscium), which is above the “V” where the two starry cords of Pisces (the Fishes) meet.
On Friday, distant blue Neptune will reach opposition, when it will be visible all night and closest and brightest for this year. Using a decent quality telescope you can see the planet among the dim stars of Aquarius (the Water-bearer). Look for the magnitude 7.8 planet sitting 1.75 finger widths to the right of the modestly bright star Phi (φ) Aquarii and 4 finger widths to the left of the brighter star Hydor (Lambda Aquarii). It will highest in the sky (best viewing conditions) at about 1 am local time.
September Dark Sky Treats
Moonless evenings in early September offer the opportunity to clearly see the Milky Way rising from the southern horizon beside Sagittarius (the Archer), arcing high overhead, and descending into the northeastern sky through W-shaped Cassiopeia (the Queen) and Perseus (the Hero). The Milky Way passes directly through the Summer Triangle of stars formed by the bright white stars Deneb, Altair, and Vega.
The glow of the Milky Way is generated by the combined light of countless distant stars. However, zones of dark dust and cold gas situated between us and those stars interrupt the Milky Way and divide it into two or more lanes in some places. The effect is particularly pronounced through Cygnus (the Swan), and southward past Aquila (the Eagle) and Serpens Cauda (the eastern half of the split constellation the Snake).
The constellation of Cygnus (the Swan) is nearly overhead in the eastern sky after dusk and nears the zenith at about 10:30 pm local time. Dark nights around the new moon are ideal times to use a telescope to see the many spectacular, but dim nebulas in the constellation. (Binoculars will work, too — from a very dark sky location.) The large North America Nebula, named for its distinctive shape and also designated NGC 7000, is a glowing hydrogen cloud located less than 3 finger widths below Deneb. Dark dust in the foreground creates the Gulf of Mexico portion of this aptly named nebula. The Pelican Nebula (also designated IC 5070) is a smaller nebula sitting just to the upper right of it. The Veil Nebula, a huge supernova remnant that is five full moon diameters across, is a broken or tattered circle of glowing gas centred 3 finger widths below (and a bit to the right of) the star Gienah (Epsilon Cygni). For best results, use the largest aperture telescope you can, and enhance these nebulas with an Oxygen-III or Ultra High Contrast filter.
Finally, use Saturn to find the spectacular nebulas Messier 20 and Messier 21 and the open star cluster Messier 21. The yellowish planet is less than 2 finger widths to the left of them.
Astronomy Skylights for this week (from September 2nd, 2018) by Chris Vaughan.
Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.