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The Sky This Week, 2018 October 16 - 23

Time to take a long look at the Moon!
The Moon, Lunation # 1165 age 10.42 days, imaged 2017 March 9
from Alexandria, Virginia with a 4-inch f/6.6 refractor telescope,
1.6X Barlow lens, and a Canon EOS Rebel T2i DSLR.
Note the prominent crater Tycho in the lower part of the Moon's disc.

The Moon waxes in the evening sky this week, climbing through the autumnal constellations as she brightens to her Full phase, which will occur on the 24th at 12:45 pm Eastern Daylight Time.  Luna spends the evenings of the 17th and 18th flanking the ruddy beacon of Mars, then passes through the sparse star fields of the autumnal constellations.  October’s Full Moon is popularly known as the Hunter’s Moon.  It has similar horizon geometry to last month’s Harvest Moon, and for folks in northern climes she will appear to rise at nearly the same time on successive nights around Full Moon.  As this extra bit of light helped farmers bring in their crops, the Hunter’s Moon provides a bit of extra light for hunters to pursue game across the stubble of the harvested fields. 

October 20th is International Observe the Moon Night, a celebration of our only natural satellite.  Its aim is to promote interest in our closest celestial neighbor, and if you own a small telescope you’re encouraged to set it up and share your views of Luna with your friends and neighbors.  We often say that the Moon is “looked over, then overlooked” by many amateur astronomers, but to me it is always an engaging body to study thanks to the detail it affords the casual viewer.  Desolate and airless, its surface reflects the violence that pervaded during the formative years of the solar system.  Its dark plains are remnants of colossal impacts of early proto-planetary bodies that smashed into Luna’s crust and liberated vast flows of lava from the still-molten interior.  The brighter areas show the effects of hundreds of other impacts that have left their marks over billions of years of geological time.  One of the most prominent of the Moon’s craters is Tycho, named in the 17th Century for Tycho Brahe, the last of the great pre-telescopic observers of the heavens.  This feature lies prominently in the battered lunar southern highlands region, and should be very prominent on the 20th.  It has a very “fresh” appearance and is the focus of an extensive system of bright “rays” that make it appear to be one of the poles on a terrestrial globe, radiating lines of longitude.  Tycho is indeed one of the youngest of Luna’s major formations, but the impact that created it occurred well over 100 million years ago when it might have been witnessed by dinosaurs.  Tycho is surrounded by hundreds of other craters that are each unique in size and appearance, and I often find myself spending a couple of hours at the eyepiece trying to take the diverse forms all in.  The Moon holds a special attraction for me, though, as I managed to travel vicariously to its environs through the flights of the Apollo missions, which began 50 years ago.  Apollo 7, the first piloted “shakedown” of the main spacecraft, flew 50 years ago this week, and it was followed by the daring flight of Apollo 8 over Christmas of the eventful year 1968.  Since that time the Moon has seemed somehow a little different to me.  Whenever I gaze at its battered face, my mind tells me “we’ve been there.”

Jupiter has just about ended his run in the evening sky fir this year.  The giant planet now sets before the end of evening twilight, but you can still catch a glimpse of him low in the southwest shortly after sunset.  He inches closer to the horizon with each passing night, but you should be able to spot him for the next few weeks.  He will pass conjunction with the Sun in late November.

Saturn hangs in the southwestern sky as twilight deepens, and by the time the sky is fully dark at around 8:00 pm he will be the brightest object in this part of the sky.  You might want to steal a glance at him if you’re out looking at the Moon during these early evening hours.  Compared to the Moon Saturn is a tiny sight, but you should still be able to discern his rings.  That said, Saturn is almost a billion miles away from us, 4200 times more distant than Luna!

Mars continues to hang just east of the meridian at the end of twilight.  He is pressing eastward along the ecliptic, currently traversing the obscure Zodiacal constellation of Capricornus, the Sea-Goat.  On the evening of the 16th he’s very close to the 5th-magnitude star Eta Capricorni. This event should be easy to see in binoculars and small telescopes.  Mars’ apparent disc has now shrunk to about half of its apparent diameter of last July’s close opposition, but you still should be able to see his bright south polar ice cap and dark surface features with a six-inch or larger telescope and a night of steady air.

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