The Moon and Earthshine, imaged 2018 January 20 from Alexandria, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor and a Canon EOS Rebel SL2 DSLR.
The Moon returns to the evening sky this week, waxing through her crescent phases as she wends her way toward the bright constellations of winter. First Quarter occurs on the 10th at 5:45 am Eastern Standard Time. As Luna passes through her crescent phases look for the phenomenon known as “earthshine”, where the part of the Moon’s disc that’s not in direct sunlight glimmers with a pale bluish tint. This glow is actually a reflection of ourselves, caused by sunlight reflecting off our blue home planet and faintly illuminating the Moon’s “night” side. On the evening of the 8th look for the Pleiades star cluster a few degrees northwest of the Moon. Can you still discern the earthshine that night?
Most of us are familiar with the expression “March comes in like a lion and goes out like a lamb”. This expression aptly describes the fluctuation of weather conditions in the northeastern U.S., where it can be cold and blustery one day and balmy the next. However, as with many such sayings, there is an astronomical connection as well. As evening twilight fades, the bright stars of winter still dominate the sky as the meridian splits the Great Winter Circle. However, quietly entering the sky in the east is the leader of the springtime constellations, the bright star Regulus. Unlike its winter companions, Regulus stands alone as the brighter stars initially command your attention, but as the night passes Regulus steadfastly climbs toward a place of prominence. Regulus, which translates from Latin origins as “Little King” is the brightest star in the constellation of Leo, the Lion, and for me is one of the sure signs of the coming spring. From suburban skies you may notice an arc of stars above Regulus that form a semicircle that outlines the regal head of the Lion. These stars form an asterism with Regulus known as the “The Sickle”, and, together with a right triangle of fainter stars to the east, outline a reasonable facsimile of a crouching beast. Leo is another ancient constellation, venerated by the ancient Egyptians as yet another embodiment of the Sun god and depicted as a lion on the famous astrological ceiling in the Temple of Denderah. Babylonian astronomers recorded the position of Regulus in 2100 BCE, and two millennia later the Greek astronomer Hipparchus used these observations to discover the 26,000-year cycle of precession of the equinoxes. In Greek mythology, Leo represented the Memaean Lion, slain by Hercules as one of his twelve labors.
Leo has a number of interesting sights for the owners of modest telescopes. While the bright winter constellations are rife with colorful stars, star clusters, and gaseous “nebulae”, the spring skies, led by Leo, offer views of distant external galaxies and colorful double stars. One of my favorite double stars lies about 8 degrees north of Regulus. Here you will find Leo’s second-brightest star Algieba, which shines with a slight yellow hue. Through a small telescope it resolves into a close pair of gold-tinted stars whose colors have a striking saturation. Under dark skies an 8-inch aperture telescope will reveal a small cluster of galaxies just two degrees north of Algieba. With a simple nudge of the telescope your view will expand from about 130 light-years for the star to 80 million light-years for the galaxies!
The bright planets are all gathering in the pre-dawn sky this week. Dazzling Venus and dimmer ruddy Mars continue to move in concert, both rising at around 4:30 am local time. They should be easy to spot by 6:00 am in the southeast.
Closer to the southeast horizon try to catch a glimpse of fleet Mercury and distant Saturn. You will ideally need an ocean horizon to get a good view, but a low, flat view to the southeast half an hour before sunrise should reveal the pair. Mercury will be just over half a degree south of Saturn and a bit brighter on the morning of the 2nd; use binoculars to try to spot the pair.