Amateur Astronomers Association of Princeton

by Jeffrey Pinyan

In an effort to remain an active participant in the AAAP while I adjust to fatherhood, I’ve decided to pen a series of informative and educational notices about selected upcoming astronomical events. I call it “Sharing the Sky”, in line with my desire to share my love of celestial observation with others.

While the observatory doesn’t open until April – and even then, we’re at the mercy of fickle Friday weather – there’s still plenty to see in the skies above in the first three months of the new year. Many of these sights require you to get up before sunrise, and some require a low horizon, so consider sharing the sky (and your equipment!) with your fellow astronomers and guests at the Washington Crossing soccer fields.

January
The Quadrantids – Jan 3-4
The new moon of Christmas waxes, but the gibbous moon will set just after midnight on January 4th, leaving the sky much darker for observing the Quadrantids meteor shower. This shower is named for the now-defunct constellation Quadrans Muralis, “the wall-quadrant”. It was created by French astronomer Jérôme Lalande in 1795, who named it Le Mural; it represented the observing instrument known as the mural (that is, wall-mounted) quadrant, used by the likes of Edmond Halley and Tycho Brahe. In 1801, German astronomer Johann Elert Bode gave the constellation its Latin name and included it in his Uranographia star atlas, but the constellation was omitted in the official list of 88 constellations established in 1922 by the International Astronomical Union.

The stars of Quadrans Muralis, situated in between Ursa Major, Draco, Bootes, and Hercules, have been subsumed into Bootes. The radiant is located nearly at the circumpolar circle, around +50° dec., just north of the head of Bootes (Nekkar [β Boo]). The meteor shower is believed to originate from the remnants of comet C/1490 Y1, observed by Chinese, Japanese, and Korean astronomers in 1490; another possible source is the asteroid 2003 EH1, which might be related to the comet. The shower is very brief in duration, generally only five days, and its peak is short-lived, as little as eight hours. The radiant will be low in the northeastern sky at midnight on January 4th, and will climb toward the zenith over the next eight hours, although the encroaching dawn will make viewing difficult by 6 AM.

Taking the Bull by the Horns – Jan 7
As sunlight fades to the west, Taurus rises in the east, with a nearly-full Moon right between his horns. The glare from the waxing gibbous will drown out other nearby stars, but the red eye of the bull, Aldebaran, still gleams less than 3° away. Prime viewing starts around 6 PM, when the Moon and Aldebaran are about 40° north of the eastern horizon, and continues until moonset around 4 AM. The careful observer will detect the Moon drifting slowly eastward away from Aldebaran, while the whole sky spins to the west. (If you miss this close pass, it will repeat on February 3rd and on March 2nd.)

The red star gets its name from the Arabic al Dabarān, “the follower”, because it follows (rises after) the nearby cluster of the Pleiades. The star also appears to be the brightest member of the Hyades open cluster that makes up the bull’s head, but this is just a trick of the light: Aldebaran is about 65 light-years from Earth, and the Hyades cluster is another 90 light-years past it (making it the closest open cluster to our solar system).

Mars at War – Jan 18
The constellation Scorpius is generally associated with the summer months, when the pincers and stinging tail crest above the hazy southern horizon during the warm nights. But the front of half of the constellation can be glimpsed low in the southeast just before sunrise during January, and in particular the “heart” of the scorpion, the red giant Antares. This unmistakably red star earned its name by seeming to complete with another red “star”, a wandering star, the planet Mars. The Greek name for Mars is Ares, and the prefix anti- means “opposed to”, so Antares is Mars’ rival owing to its brilliant red color. Mars would lose this battle, if it ever occurred – Antares is large enough that if it were placed where our Sun is, it would swallow up the first four planets easily. Its massive size comes at a price: it has a much shorter lifespan than our gentle star. At 4.5 billion years old, the Sun is only middle-aged, while the 12 million year old Antares is only a few million years from a violent end.

On occasion, the planet and the star (a mere 4.5° south of the ecliptic) come awfully close to one another. They were tantalizingly close back on the evening of August 24th, 2016 (less than 2 degrees apart). In 2020, this meeting is less close (4.5°) and less convenient – you must brave cold January mornings to watch Mars creep closer to its rival, peaking around 6 AM on the 18th. A waning crescent moon in the vicinity on the 20th (possibly tinged orange by our atmosphere) completes the scene.

February
The Moon’s Superiority Complex – Feb 18-20
Our solar system is made up of “inferior” and “superior” planets: those whose orbits are inside ours are deemed inferior, and those whose orbits are outside ours are called superior. The three closest superior planets – Mars, Jupiter, and Saturn – are visible to the naked eye, and in the early mornings of February they form a nearly straight line low in the southeastern sky. For three straight days, the Moon brushes shoulders with these three planets.

At 6 AM on the morning of the 18th, a thin crescent can be spotted about a Moon’s-width to the west of Mars. Observers west of the Mississippi would be able to watch at least some of the lunar occultation of Mars (when the Moon blocks Mars from view), but sunrise will hide that from New Jersey astronomers. An even thinner crescent can be seen 4° west of Jupiter at 6 AM on the 19th. The slightest crescent might be spotted only 2.5° southwest of Saturn on the 20th, but it will be tough: these two rise shortly before 5:30 AM, and are only about 7° above the horizon by 6 AM when the coming dawn begins to drown them out.

Growing Moon, Shrinking Venus – Feb 27
As February ends, a waxing crescent Moon appears about 6° from a waning gibbous Venus in the western sky after sunset, about 40° above the horizon around 6 PM, visible until they both set around 9 PM.

March
Martian Close Encounters – Mar 18-31
As spectacular as February’s conjunctions between the Moon and the superior planets were, March boasts even rarer views for the intrepid soul who can rise before dawn.

Over the past 30 days, Mars (for which this month is named) has inched closer to Jupiter. If you look to the east around 6 AM on March 18th, you will find a crescent Moon only 2.5° from Jupiter, with Mars half that distance from the gas giant. You can also spy Mercury “high” in the sky (around 7°) at 6:45 AM, before sunrise washes it out.

By the next morning the fading silver sliver has sped past Saturn into the faint constellation of Capricornus, but Mars goes on with the show. Before sunrise on the 20th, it’s less than 1° south of Jupiter, and as March ends, it approaches less than 1° south of Saturn.

As Far as the East is from the West – Mar 24
You have probably been noticing bright Venus in the sky after sunset since mid-December. If you’ve been an early riser, you may have been watching Mercury’s brief creep away from the overbearing Sun throughout March. Well, in just a 14-hour period, you can witness both Mercury at its greatest western elongation (about 28° from the Sun) before sunrise and Venus at its greatest eastern elongation (about 46° from the Sun) after sunset.

Unfortunately for Mercury, the days on Earth are getting longer, and so sunrise comes quickly. It will be difficult to spot this tiny, fast planet only a few degrees above the eastern horizon around 6 AM. Venus will be much easier to spot, over 30° above the western