The Evening Moon Meets Mars, Bright Pre-dawn Planets, Sirius Spikes the Football, and Bright Bino Treats!
Sirius and the Winter Football!
Happy 2019, Stargazers!
If you’ve been out under clear skies lately, you can’t have missed the sprinkling of incredibly bright and colourful stars in the eastern evening sky. Some of the brightest stars form a huge six-sided star pattern (or asterism) called the Winter Hexagon (or Football, for NFL fans).
By 8 pm local time, all of the stars that we’ll need to make the asterism are visible. The very bright, white star hugging the southeastern horizon is Sirius, nicknamed the Dog Star, in the constellation of Canis Major (the Big Dog). After our Sun, Sirius is the brightest star in all the sky. It is not only about 25 times more luminous than our Sun, but is also only a mere 8.6 light-years away! On top of that, it is actually heading towards us, and will brighten over the next millennia!
Sirius is famous for exhibiting flashes of intense colour as it twinkles. This is due to combining its brightness with the extra blanket of air it must shine though when it is low in the sky. The ancient Egyptians linked their calendar to the arrival of Sirius in the pre-dawn sky because it signaled the onset of the Nile floods around the beginning of summer. In China, Sirius is called Tiān Láng天狼, aka “the Celestial Wolf”. Many First Nations cultures saw a dog’s shape in Canis Major’s stars and called Sirius the Moon Dog Star (Inuit), the Wolf Star (Pawnee), and the Coyote Star.
Moving counter-clockwise, above and to the right of Sirius is the bright, bluish star Rigel, marking the foot of Orion (the Hunter). The constellation of Canis Major is very obviously a dog shape — with the head upwards, tail to the lower left, and feet to the west (right). Can you see the dim stars of the constellation Lepus (the Rabbit) below Orion? The big dog is chasing it!
Almost three fist diameters (26°) above Rigel is the orange star Aldebaran in the constellation of Taurus (the Bull). Aldebaran is an old red-giant star more that forty times the diameter of our sun.
Three fist diameters to the upper left of Aldebaran sits the bright yellow star Capella, the Goat Star, in the constellation of Auriga (the Charioteer). The form of Auriga is more or less a ring of medium bright stars with Capella at the top as the “diamond”. Moving three fist diameters down and to the left of Capella we encounter a pair of bright stars — the twins Castor (upper) and Pollux (lower) in the zodiac constellation of Gemini. The bodies of the twins extend sideways towards Orion.
Finally, look about midway between the twins in Gemini and Sirius for the bright blue-white star Procyon in Canis Minor (the Little Dog). At only 11 light-years away, it’s practically in our neighbourhood, too! Unlike his big brother, the constellation Canis Minor has only two significant stars. A dim, but visible star named Gomeisa sits four finger widths above Procyon.
The surface temperature of stars varies depending on their size, composition, and age, and this affects what colour we see them as. Our sun is a yellow star burning at about 5,500 degrees Celsius. Orange and red stars’ surfaces are cooler, with Aldebaran estimated to be at 3,600 degrees. White and blue stars are hotter. Sirius’ temperature is estimated to be nearly 10,000 degrees! One thing they all have in common — the cores inside the stars are at temperatures of millions of degrees! This is where the nuclear fusion that makes them shine is happening.
We can turn our football into a capital letter “G” by connecting Rigel to the bright, reddish star Betelgeuse (“beetle juice”), which marks the eastern shoulder of Orion. This star is a true giant — believed to be more than 600 times the size of the sun! It’s also nearing the end of its days — when it will explode as a tremendous supernova; but we’re in no danger when it does. Notice that Betelgeuse is not quite as strongly coloured as Aldebaran.
The Winter Hexagon is visible on the same dates and times every year, and will remain in view until about mid-April. The Winter Milky Way rises up through it — and the moon and planets wander through those stars as they travel along the Ecliptic. Next week, the nearly full moon will cross directly through the hexagon.
The Moon and Planets
The moon will traverse the dim water constellations of Aquarius (the Water-Bearer), Pisces (the Fishes), and Cetus (the Whale) while waxing towards its First Quarter phase after midnight next Sunday night. The previous night (Saturday), the nearly half-illuminated moon will pass less than a palm’s width to the lower left of bright, reddish Mars. By the time the duo sets at about 11:30 pm local time, the sky’s rotation will carry the moon higher and to the planet’s left.
Both Saturn and Mercury are too close to the sun to be seen this week, but Saturn will soon join the other two bright morning planets, Jupiter and Venus. This week, Venus will rise shortly after 4 am local time and remain visible in the southeastern morning sky until sunrise. Today, our brilliant sister planet has reached its greatest separation (or elongation, to use the astronomical term for it) of 47 degrees west of the sun for its current morning appearance. In a telescope, Venus will show a half-illuminated disk.
Very bright Jupiter will be rising soon after 5 am local time this week. Even though the big planet is moving eastward in its orbit, Earth’s motion around the sun will carry Jupiter higher and away from the sun. Meanwhile, Venus will now be swinging back towards the sun, so the two planets will “kiss” in two weeks. And amorous Venus will pass even closer to Saturn in mid-February!
Medium-bright and red-tinted Mars will continue to shine in the south-southwestern evening sky this week, although it is gradually shrinking in size and brightness as we pull farther from it. This week, the Red Planet will appear halfway up the early evening sky, and then drop into the west at 11:30 pm local time. This week, Mars will sit a fist’s width to the left of the westerly circlet of stars that form one of the fishes of Pisces (the Fishes). That ring of modest stars is about 4 finger widths across. The star that is closest to Mars, designated 19 Piscium, is a very red star, obvious when you compare it to the others in the ring. This type of star is called a carbon star because it is elderly, and is fusing carbon in its core.
This week after dusk, dim, blue Neptune will be one third of the way up the southwestern sky. The planet will set shortly before 10 pm local time, so look at it before about 8 pm, while it’s higher. Use binoculars or a telescope and look for Neptune sitting about two finger widths to the upper left of the modestly bright star Hydor (Lambda Aquarii), where it’s been for quite some time — outer planets move slowly! Hydor, and a pair of stars to its left, form a sideways narrow triangle with Neptune inside of it.
Blue-green Uranus (“YOU-ran-us”) is in the southern evening sky and will set at about 1:45 am local time. You can see Uranus without optical aid under very dark skies, but binoculars and telescopes make it relatively easy. Uranus is about 1.5 finger widths above, and slightly to the left of the modestly bright star Torcular (or Omega Piscium). That star sits a generous palm’s width above the “V” where the two starry cords of Pisces (the Fishes) meet. This week, Uranus will be at its highest point, over the southern horizon, at about 7 pm local time — the best position for seeing it clearly. Due to Earth’s faster orbit, since early August Uranus has been moving westward retrograde, compared to the distant background stars. After tonight, the planet will resume its usual eastward prograde motion.
Some Binocular Dark Sky Treats
This moonless week will be ideal for seeing the deep sky gems scattered along the winter Milky Way — and more. Here are some suggestions for your binoculars that are bright enough to see even near city lights.
After dusk in early January, the constellation of Perseus (the Hero) is positioned nearly overhead in the northeastern sky. This constellation’s location straddling the outer reaches of the Milky Way has filled it with rich star clusters. The largest of these surrounds the bright star Mirfak, or Alpha Persei. Melotte 20 (also known as the Alpha Persei Moving Group and the Perseus OB3 Association) is a collection of about 100 young, massive, hot B and A-class stars spanning 3 degrees (or six full moon diameters) of the sky. The cluster can be seen with unaided eyes, and improves in binoculars. It is approximately 600 light years from the sun and is moving through the galaxy as a group. Mirfak is moving with them. That elderly, yellow supergiant star has evolved out of its blue-coloured phase and is now fusing helium into carbon and oxygen in its core.
The northwestern region of Perseus contains the well-known Double Cluster. These two bright, open star clusters, each 0.3 degrees across and approximately 0.45 degrees apart, form a spectacular sight covering a single finger’s width of sky. If you face north, they will be located midway between W-shaped Cassiopeia (the Queen) on the lower left and the bright star Mirfak on the upper right.
You can try to see the pair of clusters without help. They’ll look like two fuzzy patches. Or use binoculars or a low power, widefield telescope to view them in all their glory. The more westerly cluster, also known as NGC 869 is more compact and contains more than 200 white and blue-white stars. NGC 884, the easterly cluster, is slightly more spread out. The clusters reside in the Perseus Arm of the Milky Way and are located about 7,300 light-years from the sun. Their region of the sky is heavily loaded with opaque interstellar dust that extinguishes their intensity.
An extra-galactic treat is nearby. After dusk on January evenings, the Andromeda Galaxy is nearly overhead in the western sky — a good position to see it through less intervening distorting air. This large spiral galaxy, also designated Messier 31 (or M31), lies only 2.5 million light years from us, and subtends an area of sky measuring 3 by 1 degrees (or six full moon diameters across and two wide). Under dark skies, the galaxy can be seen with unaided eyes as a faint smudge to the northeast of the square of Pegasus (the Horse). The three westernmost stars of Cassiopeia, Caph, Shedar, and Navi, conveniently form a triangle that points towards the galaxy. Binoculars will reveal the galaxy better. In a telescope, use low magnification and look for the two smaller companion galaxies Messier 32 close to M31’s core and Messier 110, which is farther from the core on the opposite side.