Bob Doyle, Columnist
Tomorrow afternoon, our moon’s orbiting motion will carry it from the morning to the evening side of the sun. The moon will be travelling towards the northerly zodiac groups, improving its evening visibility.
So on Tuesday, a very slender moon may be visible very low in the western dusk, setting about 8:35 p.m. Above and to the left of the moon will be Comet PAN STAARS, seen as a ‘furry star’ through binoculars.
By Wednesday, the moon will much higher (above the comet) and setting about 9:37 p.m. Each evening the comet will be farther to the North (to the right), but fading as it recedes from the sun.
PAN STARRS was a splendid sight to binocular observers in Australia during February. The comet’s close passage by the sun at midnight tonight could cause a spike in its brightness or cause it to fade.
Astronomers are hesitant to hype any approaching comet as these icy objects are unpredictable. In the early 1970’s Comet Kohoutek was billed as the Comet of the Century but was visually disappointing when it appeared in the evening sky.
On March 16 the Cumberland Astronomy Club will have a public telescope session and attempt to view Comet PAN STARRS, the moon, Jupiter and the other evening sky sights.
The session will be held at the far end (away from Main Street) of the Glendening Park Complex (off Armstrong Avenue in Frostburg).
Arrive between 7:45 and 8 p.m. so you can see the roads in the twilight. As soon as it begins to get dark, most of the telescopes will be aimed at the comet.
Since the comet will be visible only briefly, the telescopes will be later aimed at Jupiter, the moon, the Orion Nebula (star nursery). If it’s cloudy, the telescope session won’t likely be held.
This comet may disappoint but there is a night sky object that offers changing detail each night. Plus, it repeats its display of features each month.
Our moon has a number of surface features that can be glimpsed with binoculars held steadily. The most detail can be seen near the left edge of the moon (where the sun is rising). This line is called the terminator.
At the terminator, the raised rims of the lunar craters and mountains are first to catch the sunlight while the surrounding terrain is in darkness. Tomorrow will be day 0 or New Moon. This coming Thursday evening will be Lunar Day 3 when some of the larger craters can be glimpsed.
Even without binoculars, you can glimpse an oval-shaped patch near the middle of the Moon’s lighted bow. This grey lava plain is called Mare Crisium (Sea of Crises).
This huge basin likely was caused by an asteroid about 15 miles wide smacking into the moon. (Such collisions were not unusual during the first billion years after the Earth and Moon were formed, the time of the Great Bombardment).
If you use the length of Crisium (top to bottom) , then one Crisium length below is a crater called Langrenus about 82 miles across. Going above Crisium is another big crater called Petavius, about 110 miles wide.
You may wonder how the size of these craters are known. Through the laser reflectors left on the moon by the Apollo missions, astronomers know the moon’s distance very accurately.
There is also an allowance for foreshortening as the three-day moon features are seen at a glancing angle. Most craters on the moon (formed by impact) are quite circular.
This Saturday will be Lunar Day 5. At that time, several more grey lava plains will be visible. Below Mare Crisium is Mare Fecunditatis (Sea of Fertility).
To the left of Mare Crisium is Mare Tranquilatitis (Sea of Tranquillity), the lava plain where our first manned lunar landing took place in July 1969. Below Tranquillatitis is the smaller Mare Nectaris (Sea of Nectar).
You may be wondering about the names for the lunar lava plains. When the moon was first observed with telescopes, scientists were convinced that the moon had to be like the Earth with oceans, seas and dry land areas. So these large features were named in the 17th century and never changed.
It was also believed that the moon had an atmosphere and was probably inhabited. (For why would God have made the moon unless he created creatures to live on it?)
A prominent 17th century scientist named Christian Huygens (who discovered the rings of Saturn) published a book speculating on the creatures that lived on each planet.
SKY SIGHTS AHEAD: Hope for clear weather from Wednesday on so Comet PAN STARRS can be seen with binoculars in the early dusk close to the western horizon. But even if there is a little haze, you can still watch the moon with binoculars.
I will continue my description of the moon’s surface features in my next column. On March 17 the moon will appear close to the bright planet Jupiter.
Bob Doyle invites any readers comments and questions. E-mail him at firstname.lastname@example.org . He is available as a speaker on his column topics.