The Moon and Planets
The moon will be rising late this week, appearing over the eastern horizon after midnight local time and then lingering into the morning daytime sky. It will reach its Last Quarter phase on Tuesday morning. At that time, it will sit at a 90° angle to the sun and Earth, and appear half illuminated, on the left-hand side (as viewed from the Northern Hemisphere).
In the pre-dawn eastern sky on Wednesday morning, the eastward orbital motion of the waning crescent moon will carry it less than 2 finger widths to the lower right of the large open star cluster known as the Beehive (or Messier 44). Minimum separation will occur at about 5 am EDT. During the coming weekend, the slim crescent moon will make a pretty sight low in the eastern sky before dawn.
This week, very bright Venus will be visible low in the western sky for only a short period after sunset. Tonight, it will set at 7:35 pm, only 40 minutes after the sun. In a small telescope, Venus’ disk will resemble a slim crescent moon, lit only on the sunward side (although your telescope might flip the view). The planet is still growing larger in apparent diameter because it is travelling towards the Earth right now.
Jupiter has been carried towards Venus by the westerly motion of the sky. This weekend, it is only 1.4 outstretched fist diameters to Venus’ upper left. But Venus is outpacing Jupiter as she swings towards the sun — so they won’t get closer than they are now. We are finished with decent telescope views of Jupiter for this year. By the time the sky gets dark at 8 pm local time, the mighty planet will sit less than a fist’s diameter above the southwestern horizon. It will set in the west-southwest at about 8:45 pm local time. Using binoculars, try to see Jupiter’s four Galilean moons (Io, Europa, Callisto, and Ganymede) forming a line to either side of the planet.
Brighter, reddish Mars and dimmer, yellow-tinted Saturn occupy the southern sky after dusk now. At 8 pm local time, both planets will be about two fist diameters above the horizon, with Mars about 3 fists east (left) of Saturn. Mars will set in the west after 1:30 am local time. It’s still well worth looking at, even in a small telescope. Try to see a small white oval near the top of its disk. That’s the southern polar cap!
Saturn will set in the west before 11:30 pm local time. 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 its largest satellite, Titan. Using a clock’s dial analogy, Titan will move counter-clockwise this week — from a position at 11 o’clock (nearly above Saturn) to 7 o’clock (nearly below Saturn). (Remember that your telescope might flip and/or invert the view. Use the moon to find out how your telescope changes things and keep a note of it, since that will always be the case.)
Distant Neptune recently reached opposition, so it is visible all night and almost its closest and brightest for this year. Using a decent quality telescope you can see the very blue planet among the dim stars of Aquarius (the Water-bearer). Look for the magnitude 7.8 planet sitting midway between the modestly bright star Phi (φ) Aquarii and the brighter star Hydor (Lambda Aquarii). It will highest in the sky (best viewing conditions) at about midnight local time.
Blue-green coloured Uranus is visible nearly all night, too. You can see it without optical aid under very dark skies, but binoculars and telescopes work better, especially with this week’s bright moon. The ice giant planet is located in the eastern mid evening sky, about 4 finger widths to the left of the modestly bright star Torcular (Omega Piscium). That star sits a generous palm’s width above the “V” where the two starry cords of Pisces (the Fishes) meet. Through the night, the planet will be carried higher — making it easier to see.
Seeing Giant Galaxies
This is the season to look for the farthest object a human eyeball can see without help* — the Andromeda Galaxy, or Messier 31. This large spiral galaxy is a sister to our own Milky Way galaxy. It sits 2.5 million light-years away from our sun, meaning that its stars’ light has been journeying for that length of time. And, if there are alien astronomers there looking at us, they are seeing our solar system as we were 2.5 million years ago!
Under dark skies, using unaided eyes only, you should be able to see a faint fuzzy patch that is elongated left and right. The galaxy spans six full moon diameters across the sky, but only its bright core and surrounding, dimmer halo are usually seen visually. It’s quite easy with binoculars.
Because their fields of view are too narrow to see the entire galaxy, small telescopes generally only show its bright core. Be sure to look for M31’s two companions, the small elliptical galaxies designated M32 and M110. M32 is close to the big galaxy’s core and situated just to the lower right. M110 is above the main core and slightly farther away. At 2.49 million light-years, M32 is closer to us than the Andromeda Galaxy. M110 is 200,000 light-years farther away.
To find M31, you can first find the medium-bright star Mirach. It’s the second star east of the eastern corner of the Great Square of Pegasus. Then look for a dimmer star about 4 finger widths above Mirach. The galaxy is higher by the same distance. Alternatively, you can use the highest three stars of the W-shaped constellation Cassiopeia (the Queen). Those three bright stars form an arrow that points directly at M31.
*Another large galaxy, called Messier 33 in Triangulum (the Triangle), is 2.75 million light-years away. Observers with very keen eyes under very dark sky conditions can sometimes see it, too — setting the record. This galaxy is tougher because it is oriented nearly face-on to Earth — so its light is spread across a larger patch of sky, making it dimmer overall. It sits only 1.3 fist diameters below M31, a palm’s width below the star Mirach.
Astronomy Skylights for this week (from September 30th, 2018) by Chris Vaughan. Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.