This is Dudley Observatory’s Skywatch Line for Friday, March 4, through Sunday, March 6, 2016, written by Alan French.
The Moon reached last quarter last Monday and is now moving toward new, which occurs this coming Tuesday. A slender old Moon will grace the morning sky before sunrise.
At 5:30 AM on Saturday morning a 17-percent illuminated crescent Moon will be low in the southeast, just under 14 degrees above the horizon. At the same time Sunday morning, an even thinner crescent – just 9-percent in sunlight, will be just over 7 degrees above the horizon in the east southeast.
The dark moonless skies this weekend are ideal for enjoying the beauty of the winter sky before it vanishes in the west. At 8:00 PM the familiar bright stars of winter are almost due south, with brilliant Sirius, the brightest star in the night sky, 30 degrees above the horizon.
Sirius is bright mostly because it is a nearby neighbor, lying at a distance of just 8.7 light years. With a luminosity of a bit over twenty times that of our Sun, it is pretty typical of the stars we see.
It can be hard to get a real concept of the vastness of space and the large distances between our solar system and even our nearest neighbors. A popular model of our solar system begins with a Sun the size of a bowling ball. On this scale our Earth is the size of a peppercorn and is 26 yards from the bowling ball Sun. The farthest planetary member of our solar system, Neptune, would lie 778 yards away and be the size of a peanut.
When we start adding the nearby stars to our model, the distances grow much larger. In our model, Sirius would lie 8,070 miles away. The nearest star in our nighttime sky, Proxima Centauri, would be 4,000 miles from our bowling ball Sun.
If you are away from the light polluted skies of our cities and larger towns, look for the band of light that marks the winter Milky Way, stretching upward a bit east of due south, passing east of Sirius, up above Orion, and passing west of bright Capella high overhead. The Milky Way narrows and dims past Capella, then brightens and broadens as it move down toward the north northwestern horizon.
In the winter we are looking outward in our galaxy, away from its center. The region of Taurus and Auriga, where you see a marked dimming, is directly away from the galactic center. Largely because there are fewer stars in the outer part of the galaxy, this part of the Milky Way is faint.
The region passing through the conspicuous “W” pattern of stars marking Cassiopeia is quite rich in stars. It’s a wonderful area to explore with binoculars, especially from the comfort of a lawn chair.