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The Sky This Week, 2019 February 5 - 12

Reflections on the Moon
The Moon with Earthshine, HDR composite imaged 2018 January 20 from Alexandria, Virginia
The Moon with Earthshine
HDR composite imaged 2018 January 20 from Alexandria, Virginia
with a 102mm (4-inch) f/6.5 Explore Scientific AR-102 refractor
and a Canon EOS Rebel T2i DSLR.

The Moon waxes in the evening sky this week, climbing through the dim autumnal constellations toward the bright stars of winter.  First Quarter occurs on the 12th at 5:26 pm Eastern Standard Time.  Look for ruddy Mars to the north of the Moon on the evening of the 10th.  On the evening of the 12th Luna forms an attractive triangle with the bright star Aldebaran and the Pleiades star cluster.

As the Moon moves into the evening sky you have an excellent to follow the advancing terminator, the line demarcating sunrise on the lunar surface, as it advances each passing night.  During the first few evenings of the week look for the ghostly glow of “earthshine” bathing the un-sunlit part of the Moon’s disc with a subtle bluish tint.  This faint light is produced by sunlight reflecting off of Earth, illuminating the portion of the Moon facing us that’s not under direct solar illumination.  The blue tint is a signature of how Earth looks from space; as evidenced by the pictures returned by the Apollo astronauts some 50 years ago, our planet is truly a “blue marble” in space.  Earthshine is best seen with the naked eye about two to four days after New Moon, but you can see it with a small telescope up until First Quarter.  If you were standing on the Moon’s surface, Earth would show a complimentary phase to the lunar phase we see here.  When Luna is a crescent, Earth would be a bright gibbous in the lunar sky, and it would wane as the Moon’s crescent waxes for Earth-bound observers.  Late winter and spring are the best times to look for this phenomenon since the Moon climbs rapidly above the horizon on successive evenings as she moves through these early phases.  It’s also a great time to explore the amazing landscapes that are revealed by the slowly-advancing terminator each night.  The relatively smooth plains that are known as the lunar “seas” offer a stark contrast to the myriad of impact craters that pepper the landscape.  These circular scars are a mute testament to the violence of the Moon’s formation.  With no flowing water or atmosphere the lunar surface preserves events that occurred billions of years ago when the solar system was populated with billions of “planetessimals” that collided with each other and accreted into the large worlds we see today.  Looking at the Moon in the small telescope is looking back to an epoch older than 99-percent of the present surface of the Earth.

As the Moon waxes the fainter stars of the sky begin to wash out with the increasing lunar glow.  The bright winter constellations stubbornly resist this luminous intrusion, and to my eyes the brighter background glow only enhances the colors of the season’s stars.  The ruddy tints of Aldebaran and Betelgeuse become more apparent, while the contrasting blue of Rigel and Sirius seem accentuated.  Of all the bright stars of winter, though, my favorite is Capella, which passes directly overhead at around 8:30 pm.  Capella has a wonderful warm yellow glow that I don’t see in any other first-magnitude star.  Capella’s spectral class is close to that of our Sun, so it is probably quite analogous to what our star would look like if we could see it from the environs of the closest star system, Alpha Centauri.  

The early evening sky still hosts Mars, which is moving steadily toward the east against the faint stars of Pisces.  By the end of the week Mars is crossing the imaginary boundary between Pisces and Aires.  On the evening of the 12th you have an opportunity to track down a much more distant world as Mars passes just one degree north of the planet Uranus.  If you have a pair of binoculars you should be able to easily spot Uranus as the southern apex of a triangle with Mars and the sixth-magnitude star 54 Ceti about a degree to the east.  Uranus is a tad brighter than the star and has a faint greenish tint.  If you have a small telescope you should be able to resolve Uranus’ small disc, which will be just over half the size of the ruddy face of Mars.

The next bright planet won’t reveal itself until early morning, where you’ll find bright Jupiter in the southeastern sky with the first rays of the coming dawn.  Old Jove is about 10 degrees northeast of Antares, the ruddy heart of Scorpius, one of summer’s signature constellations.  

Bright Venus follows Jupiter as the morning sky brightens before sunrise.  She reaches her most southerly declination on the 10th.  She will continue to edge closer to the Sun over the next few weeks, then linger in the twilight hour until late summer. 

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