Walking the Dog on Moonless Nights, Evening Mars and Pretty Pre-dawn Planets!
Evening Zodiacal Light
For about half an hour after dusk between today and the new moon on March 6, look west-southwest for a broad wedge of faint light rising from the horizon and centered on the ecliptic. This is the zodiacal light — reflected sunlight from interplanetary particles of matter concentrated in the plane of the solar system. The glow will be centred on the horizon directly below Mars. Try to observe from a location without light pollution, and don’t confuse the zodiacal light with the brighter Milky Way to the northwest.
Walking the Big Dog
The night sky’s brightest star Sirius is sure to catch your eye in the evening sky this time of the year. Once the sky darkens at around 8:30 pm local time, Sirius will be sitting a third of the way up the southern sky, to the lower left of Orion (the Hunter). During the rest of the evening, Sirius will slowly descend into the southwestern sky and set just after midnight local time.
Sirius name means “searing” or “scorching” in Greek. It’s also commonly known as the Dog Star because it is the brightest star in Canis Major (the Big Dog). To my eyes, the constellation genuinely resembles a wiener dog! Sirius sparkles at the dog’s collar. The pup’s head is formed by several medium-bright stars to Sirius’ upper left, but those are near the limit of visibility in urban skies. Nose to tail, the constellation measures about 19°, or two fist diameters held at arm’s length. He’s about one fist from ears to paws. The rest of the dog’s body, composed of more easily visible stars, extends to the lower left (southeast) of Sirius. The dog is rearing up and facing west, as if he is begging Orion for a treat.
About a fist’s diameter below Sirius is the bright star Wezen, which marks the dog’s “bottom”. Wezen, Arabic for “weight” is a rare, massive yellow supergiant star. One day it will explode in a supernova. The tip of the dog’s tail, marked by a modest star named Aludra, is found 4° (four finger widths) to the lower left of Wezen. Four degrees to the lower right of Wezen, a bright star named Adhara represents the dog’s rear legs. (Some representations include two dimmer stars for the rear paws.) Adhara is a hot blue giant star with a surface temperature of a whopping 21,000 K located about 34 light-years from the sun. It’s the brightest star in the sky when viewed in ultraviolet light, and it, too, is on the way to a supernova death.
The dog’s front legs are formed by the bright star Mirzam, which is located about a palm’s width to the lower right of Sirius. Mirzam, which means “the Herald” because it rises just before Sirius, is 60 times more luminous than Sirius. If it were located where Sirius is, instead of 500 light-years away, it would appear 15 times brighter than Venus!
In the heart of Canis Major, about four finger widths below Sirius, is a bright little cluster of stars designated Messier 41, sometimes called the Little Beehive Cluster. Binoculars should show it easily. The cluster, which is about 2300 light-years away, consists of several brighter golden stars and numerous fainter ones. Another nice cluster sits about 2.5 finger widths to the upper left of Wezen. Scan around that area of sky with your binoculars — the winter Milky Way has populated Canis Major with many treats.
Canis Major is only one of Orion’s two hunting companions. The other one, Canis Minor (the Smaller Dog), sits 30° (three fist diameters) to Orion’s left. This constellation is composed of only two stars — very bright white Procyon and dimmer Gomeisa, which sits about four finger widths to Procyon’s upper right. Ironically, the constellation resembles a stick more than a dog! The two dogs might well be hunting Lepus (the Rabbit), a constellation of modest stars that sits directly below Orion.
Sirius is so bright because it is about 25 times more luminous than our Sun, and only a mere 8.6 light-years away from Earth. Furthermore, it is heading towards us, and will brighten over the next millennia! Sirius has a tiny companion star, designated Sirius B, that some astronomers call the Pup. I prefer to call it the Flea!
Sirius is famous for exhibiting flashes of intense colour as it twinkles. This is because northern hemisphere observers usually see the star positioned low in the sky, so its very bright starlight is passing through a thicker blanket of air. The pockets of turbulence in our atmosphere that makes stars twinkle also work like tiny refracting prisms — splitting apart Sirius’ white starlight and randomly sending different colours (wavelengths) to our eyes.
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 these stars and called Sirius the Moon Dog Star (Inuit), the Wolf Star (Pawnee), and the Coyote Star. On the next clear evening, have a look at our bright neighbour!
The Moon and Planets
The moon will start the week as a slim, old crescent sitting low in the southeastern sky before sunrise. Even though New Moon won’t occur until Wednesday morning, the shallow angle of the moon’s orbit this time of year will cause the moon to rise almost beside the sun, hiding it from view for several days.
The moon will return to view as a young, slim crescent sitting low over the western horizon on Thursday evening right after sunset. At the same time, sharp eyes might catch Mercury sitting 8.5 degrees to the right of the moon. The best time to look for Mercury will be around 7 pm local time. The moon will complete the week by waxing fuller daily and climbing higher — landing a fist’s diameter below Mars on Sunday evening.
Speaking of Mercury, during the first half of this week, the normally elusive planet will continue to be easily visible in a darkening western evening sky while it descends toward the sun. The optimal viewing times will fall between 6:45 and 7:15 pm local time. If you view Mercury in your small telescope, the planet will exhibit a waning half-illuminated disk. Find a viewing spot where the western horizon is low and free of foreground obstructions. Once the sun has fully set, sweep the sky with binoculars — or your own sharp eyeballs — looking for a medium bright, unmoving point of light.
The other easy evening planet to see this week will be Mars. When the sky begins to darken, Mars will appear as a medium-bright, reddish pinpoint of light about halfway up the western sky. The Red Planet will set at about 11:15 pm local time. Mars has been slowly shrinking in size and brightness as we increase our distance from it little-by-little.
The much dimmer, blue-green planet Uranus is also in the western early evening sky. It can be identified by aiming binoculars about 1.6 finger widths above the modestly bright star named Torcular (or Omega Piscium). Look for Uranus right after dark — this week the distant ice giant planet will set at around 10 pm local time.
Three spectacular bright planets — Jupiter, Saturn, and Venus, will all continue to appear low in the eastern morning sky this week. Bright Jupiter will rise first, at about 2:30 am local time. By 7 am local time, it will be a beacon in the southern sky. Yellowish Saturn, which is twice as far away as Jupiter, is correspondingly dimmer. The ringed planet will rise at about 4:15 am local time and will be lost in the twilight by 7 am. Our sister planet Venus is only one-fifth as far from Earth as Jupiter. Venus’ blazing brilliance will grace the southeastern dawn sky after 5 am local time, and remain in view until sunrise. In a telescope, Venus will exhibit a gibbous (more than half-illuminated) phase.
Astronomy Skylights for the week of March 3rd, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!
