Bob Doyle, Columnist
Last week, the slender crescent moon and a modest comet (PAN STAARS) appeared in the western dusk sky.
With the evening moon becoming much brighter this week, it will be harder to see the comet through the moonlight. Binoculars are recommended.
The comet tonight is the star group Pisces, seen low in the western dusk and only about 18 degrees from the sun. PAN STARRS is moving nearly northward.
On the evening of March 21, the comet will move into the star group Andromeda, being at an angle of 22 degrees from the sun. As March ends, PAN STARRS will be near Andromeda’s shoulders and about 30 degrees from the sun.
While the larger angle to the sun will make it easier to spot, the comet will also be even fainter as it moves away from the sun.
Today, the length of daylight and night are equal. It is widely believed that this condition occurs at the equinoxes, the start of spring and fall.
But on these dates, daylight is about 8 to 10 minutes longer than night. This is due to the sun’s image being lifted about one-half of a degree when it is rising or setting. This bending is caused by the refraction or bending of light when the sun’s light enters the atmosphere at a large angle to the vertical.
So we see the sun rising about four minutes before it actually breaks above the horizon. When the sun appears to set, we see the top of the raised image of the sun four minutes after the sun has dropped below the horizon.
This raising effect is a minimum at the equator where the sun rises and sets vertically, not at a slant as in our area. (Of course, the sun neither rises or sets; it’s the rotating Earth that makes the sun seem to be moving.)
This evening the nearly half-full moon appears near the bright planet Jupiter. The two objects will be only three moon widths apart (1.5 degrees) at 9 p.m. when the sky is quite dark.
Tonight is Lunar Day 6, six days after the moon swung past the sun (New Moon) in going from the morning to the evening side of the sun.
Even without optical equipment, the dark grey plains on the upper half of the moon’s lighted bowl are easy to spot. The detached grey spot is Mare Crisium, a cooled lava basin over 300 miles across.
Three of the other grey plains are clumped together. Nearest is the larger Mare Tranquillitatis, where Apollo 11 (our first manned lunar landing ) set down.
Below Tranquillitatis is the Mare Fecunditatis lava basin, comparable in area to Mare Crisium. Mare Serenitatis is above Tranquillitatis and comparable in size.
With binoculars held steadily this evening, some of the larger craters are in view.
About halfway along the left edge of the moon is the crater Ptolemaeus, named for Astronomer Ptolemy that is nearly 100 miles across. Below and farther to the right (west) is the crater Maurolycus about 75 miles wide.
On Lunar Day 9 (March 20), more large grey plains have rolled into the sunlight. On top is Mare Imbrium. Below Imbrium are three overlapping lava fields.
Binocular viewers will see a very prominent crater in the midst of these lava fields. This is Copernicus, 56 miles across with walls that rise 12,000 feet above its surroundings.
By this Saturday night (Lunar day 11), there is a prominent crater whose bright rays splash across the grey plains as well as the lighter plains (called the Lunar Highlands). This ray system is visible to the eye but the crater requires binoculars.
The crater is Tycho, named for the best observer of stars and planets before telescopes. Near the bottom of the moon is the dark crater Plato (for the famous philosopher).
SKY SIGHTS AHEAD: Orion is now in the southwest evening sky, following Taurus and Jupiter. Orion’s belt points left to Sirius, the night’s brightest star.
Sirius is also the closest star we can see in the night sky, at a distance of nearly nine light years. Lower in the west is the Seven Sisters or Pleiades star cluster, a beautiful sight through binoculars.
The Big Dipper is high in the north and upside down. The leftmost stars of the bowl point down to the North Star, a modest star about which the heavens seem to circle. (The Earth’s North Pole nearly points to the North Star (also known as Polaris).)
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.