Pointing at Polaris, Bright Pre-dawn Planets, and an Enticing Evening Moon!
Detect the Little Dipper
Polaris, the North Star, is the star at the tip of the handle of the Little Dipper, the asterism we also know as the constellation Ursa Minor (the Little Bear). Contrary to popular opinion, Polaris is not a prominent star at all. It is ranked only 48th in brightness — but nevertheless it can easily be spotted with mere eyeballs in a moderately dark sky, if you know where to look. Polaris is located about 430 light-years from Earth. Its surface temperature is similar to our sun’s, but the star is much larger, and it emits 2500 times the light of our sun.
Polaris’ fame is due to its steadfast position over the northern horizon. While the rest of the sky revolves due to Earth’s rotation, Polaris remains anchored in place because it sits less than a finger’s width from the North Celestial Pole, the imaginary point in space that the Earth’s axis of rotation points at. Due to Earth’s precession, the slow wobble of the Earth’s axis, Polaris will slowly drifting closer to the pole until the year 2101. The star Thuban in Draco (the Dragon) was the pole star when the pyramids were built.
You can measure your latitude on Earth by counting how many degrees above the horizon Polaris is. Combine that knowledge with the fact that Polaris marks where the compass direction of north is, and you’re well on your way to figuring out your location on Earth — at least, that’s what folks did before GPS!
The easiest way to find Polaris is to use the outermost stars in the Big Dipper’s bowl. Join an imaginary line from Merak (the bottom of the bowl) to Dubhe (at the rim of the bowl) and keep going. Polaris is the next obvious star you’ll come to. It’s about three fist diameters from Dubhe. Don’t forget that the Big Dipper, like everything else in the sky, circles around Polaris continuously. Sometimes you’ll be drawing that line upwards, and sometimes to the left or the right. In March annually, you’ll find Polaris it downward and to the left of the dipper. Merak and Dubhe are often referred to as the Pointers.
If you have a telescope, aim it at Polaris and look for a dim, white-coloured partner star sitting near more yellowish Polaris. Once again, the little star can be anywhere on a circle surrounding Polaris. On mid-March evenings, the companion will be to the lower left, but your telescope’s optics will probably flip it to another orientation. That little star can be joined up with more stars to form a small, roughly circular ring of dim stars on the side of Polaris opposite to the Little Dipper’s bowl. It’s called the Engagement Ring, and Polaris is the diamond. Let me know if you see it.
In mid-March at around 9 pm local time, the rest of the Little Dipper extends sideways to the right from Polaris, and curves strongly upwards towards the Big Dipper. The two dippers fall on either side of the tail stars of Draco. The magnitude 2.06 star at the outer edge of the Little Dipper’s bowl (and closest to the Big Dipper) is slightly dimmer than Polaris. This medium-cool, reddish star is named Kochab. The other five stars of the constellation may be too dim to see from the city, but binoculars will reveal them. Good luck!
The Moon and Planets
This week, the moon will entice you to gaze upon it after dinner. It will spend the week waxing fuller while it climbs the western evening sky. When the moon is at this stage of its monthly journey around Earth, the sun is slowly rising over the moon’s eastern horizon. The slanted “dawn” sunlight casts long, deep black shadows to the west (our left) of any elevated feature on the moon — including crater rims, mountain chains, ridges, and fault scarps. For the best views, point your binoculars or telescope along the strip flanking the pole-to-pole line that divides the lit and darkened hemispheres. And remember, when the majority of the side of the moon we see is dark, the far side is mostly lit. In other words, it’s wrong to refer to the part of the moon we never see as the dark side, because it’s only dark half of the time!
On Monday evening, the waxing crescent moon will be positioned a palm’s width below Mars. The duo will set at about midnight local time. At the same time, you might notice a rough circle of medium-bright stars to the moon’s left. That’s the head of Cetus (the Whale). The brighter, warm-coloured star positioned a fist’s diameter to the left of the moon is named Menkar. That star’s formal designation is Alpha Ceti, “the brightest star in the whale”. In Star Trek lore, Ceti Alpha V was the planet around that star that James Kirk marooned Khan Noonian Singh and his group on in the Original Series episode “Space Seed”. It was later featured in “The Wrath of Khan”. Take a look!
On Wednesday evening, the moon will land just below the triangle of medium-bright stars that form the face of Taurus (the Bull). Stargazers in western North America will see the moon approach close to the bright, orange-ish star Aldebaran (the eye of the bull) before both objects set in the west. Wherever you live, look a fist’s diameter to the right of the moon for the Seven Sisters, the small, bright cluster of stars that form the logo for the Subaru car company. The sisters were the daughters of Atlas and Pleione in Greek mythology. We also call this object the Pleiades cluster and Messier 45.
On Thursday morning, the moon will reach its First quarter phase, when it will sit at a 90° angle from the sun and will appear half-illuminated. First quarter moons rise around noon and set around midnight, so they become visible starting in the afternoon. The term quarter moon refers not to its appearance, but the fact that our natural satellite has now completed the first quarter of its orbit around Earth since the last new moon.
On Thursday evening the moon will tickle the toes of Gemini (the Twins). On Saturday night, the waxing gibbous moon will be positioned about a palm’s width to the right (west) of the large open star cluster known as the Beehive or Messier 44 in the constellation of Cancer (the Crab). The moon encounters the cluster frequently because the Beehive is located only 1 degree north of the ecliptic, the great circle around the sky that most solar system objects orbits are close to. To see the cluster’s stars, try placing the bright moon just outside the field of view of your binoculars. The following evening, the moon will hop past the cluster to sit a similar distance to the lower left (east) of the “bees”.
As I referenced above, Mars will be an easy planet to see every evening this week. When the sky begins to darken, look for Mars as a medium-bright, reddish pinpoint of light less than halfway up the western sky. The Red Planet will set at about midnight local time. Mars has been slowly shrinking in size and brightness as we increase our distance from it little-by-little.
The remaining bright planets have been hanging out in the eastern pre-dawn sky, and they’re putting on quite a show. Bright Jupiter will rise first, at about 3 am local time. By 7 am local time, it will be a beacon in the southern sky. Yellowish Saturn, which is somewhat dimmer due to its greater distance from Earth and its slightly smaller diameter, will rise at about 4:45 am local time and will be lost in the twilight by 7 am.
Our sister planet Venus is now getting markedly closer to the sun and will soon disappear into the dawn twilight. Venus’ blazing brilliance will grace the lower part of the southeastern dawn sky after 6 am local time, and remain in view until sunrise. In a telescope, Venus will exhibit a gibbous (more than half-illuminated) phase. If you have trouble seeing Saturn, search about midway between Jupiter and Venus.
Astronomy Skylights for the week of March 10th, 2019 by Chris Vaughan.
Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!