Touring Winter Evenings’ Brightest Stars, and a Morning Moon meets Mars and Jupiter!
The Bright Stars of January
The cold clear nights of winter have arrived. Let’s review the many bright stars you can pick out with your unaided eyes in the evening sky over the next month or so. I’ve put their brightness rankings (3rd brightest in the night sky, 7th, etc.) in brackets.
Let’s start in the western half of the sky because those stars set first. If you have an open southwestern horizon, look as soon as it’s dark for bright Fomalhaut (18th) very low in the southwestern sky. Looking directly west, the three bright corners of the Summer Triangle still shine brightly in the early evening. The lowest of the three is Altair (12th) in Aquila (the Eagle). A bit higher, and about 3.4 outstretched fist diameters to the right of Altair, is Vega (5th) in Lyra (the Lyre). Deneb (19th) sits above and between those two. All three are hot, bluish white stars. Deneb is the tail of Cygnus (the Swan), and you should be able to see the great bird flying head-down into the west — along the Milky Way. Altair and Vega set about 7:30 and 9 pm local time, respectively. Deneb sets much later — at about 1:15 am local time.
Next, turn fully around and look about halfway up the eastern sky. Bright yellowish Capella (6th) is on the left and orange-ish Aldebaran (14th) is located about three fist widths to the right of it. Capella is the brightest star in the large circular constellation of Auriga (“Oar-EYE-gah”) (the Charioteer), while Aldebaran is the baleful red eye of Taurus (the Bull), whose triangular face is tilted sideways to the left. Both of these constellations will be higher in late evening.
The well-known constellation of Orion (the Hunter) sits directly below Aldebaran. His eastern shoulder is the old and bright reddish star Betelgeuse (11th), and his opposite foot is a bluish star of similar brightness named Rigel (7th). These two stars are hundreds of light-years away. Orion’s three-starred belt is a highlight of the winter sky. From east to west (lower left to upper right) they are Alnitak (30th), Alnilam (29th), and Mintaka (67th). The three stars are evenly spaced — almost exactly 1.3° (about three moon diameters) apart. Orion’s other shoulder is marked by bluish white Bellatrix (26th), and his opposite foot is called Saiph (53rd).
To the left of Orion sits the zodiac constellation of Gemini (the Twins). Its brightest stars are yellowish Pollux (17th) and pale white Castor (23rd). Like many twins, they are a challenge to keep straight which is which. Castor, the higher star, rises first, just as “C” precedes “P” in the alphabet.
The night sky’s brightest star rises in the sky below Orion after 7 pm local time. Sirius (1st), also called the Dog Star because it resides in the constellation of Canis Major (the Large Dog), is a very hot, bluish-white star. It’s so bright because it is our neighbour — positioned “just up the street” at only 8.6 light-years away. Sirius has a reputation for twinkling vigorously with flashes of pure colour. This is because it sits fairly low in the sky for mid-latitude residents, and we see it shining through a thicker blanket of refracting air. Sirius’ bright little sibling Procyon (8th) sits 25° (2.5 fist widths) to the upper left, under Gemini, in the constellation of Canis Minor (the Little Dog). It, too, is relatively close to Earth.
In January, these stars reach their highest points, in the southern sky, before midnight — perfect to catch your eye through a south-facing window before bedtime. Good hunting!
The Moon and Planets
This week the moon will complete its monthly orbit around the Earth. It reaches its Last Quarter phase on Monday afternoon. The times when the moon’s phases happen are dictated by when the appropriate angles are formed by the sun, Earth, and moon. They are independent of the Earth’s rotation, so they can happen any time of the day or night. Last quarter moons are always half illuminated — on the left-hand side for observers north of the equator, and the reverse for southerners (where the moon appears “upside-down”). They rise around midnight, and linger into the daytime morning sky.
After Monday, the moon will wane towards a thin crescent and rise even later. And this sets up a journey through the pre-dawn stars and planets in the eastern sky. On Tuesday morning, the moon will land a palm’s width to the upper left of Spica, the brightest star in Virgo (the Maiden). On Thursday morning, the waning crescent moon will sit less than 4° (about four finger widths) to the upper left of dim reddish Mars and very bright Jupiter. The two planets will be separated by only two finger widths, so all three objects will fit nicely within the field of view of binoculars. The dim stars around the trio form the constellation of Libra (the Scales). The moon will meet up with more planets next week.
The pre-dawn planet party is still going strong! Jupiter is the very bright object glowing in the eastern sky until dawn, when it’s well above the southeastern horizon. You might have noticed that Jupiter’s orbital motion has carried it farther away from the double star Zubenelgenubi in Libra (the Scales) which is now sitting about three finger widths to the upper right of the King of Planets. This increasing separation will continue until late winter. Then Jupiter will temporarily reverse direction and perform a retrograde loop towards, and then past, Zubenelgenubi until July, before resuming its regular eastward travel.
This weekend, reddish Mars made a very close pass of Jupiter. From this point onward, the much dimmer red planet will stay in roughly the same spot in the morning sky while Jupiter and the surrounding constellations slide higher due to Earth’s motion around the sun. Mars rises shortly after 3 am local time this week. Scan the sky to Jupiter’s lower left to find it, even as dawn arrives. Mars will steadily brighten over the next seven months.
Last Monday, Mercury reached its greatest angle west of the sun and started swinging towards the sun again. You can still try to see it very low in the east between about 6:45 and 7 am local time. To unaided eyes, Mercury will resemble a medium bright “star”. This coming weekend, Mercury will pass close to Saturn. The two planets will be less than a finger’s width apart on Saturday. Mercury will be brighter and lower. Look for them between about 6:30 am and 7 am local time.
Saturn will climb higher every morning during the next few months. It passed the sun a few days before Christmas and officially joined the morning sky. In a similar way, both Venus and Pluto are passing the sun early this week.
Until Jupiter begins rising before midnight on March 4, Uranus and Neptune are the only evening planets for the next two months. They’re both in the southwestern sky, but they are challenging to find and observe.
Astronomy Skylights for this week (from January 7th, 2018) by Chris Vaughan.
Keep looking up to enjoy the sky! I love getting questions so, if you have any, send me a note.