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Follow That Moon!

21 February 2023

21 February 2023

The Moon, imaged 2022 December 31, 00:46 UT, from Alexandria, Virginia
with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, Antares 1.6X Barlow lens,
and a ZWO ASI18MC CMOS color imager.

The Moon returns to the evening sky this week.  You should be able to see her very thin crescent shortly after sunset, about seven degrees below Venus in the western sky.  On the following evening she passes just over a degree from bright Jupiter, setting up a nice photo opportunity in the twilight sky.  First Quarter occurs on the 27th at 3:06 Eastern Standard Time.  Luna can be seen just two degrees east of ruddy Mars on the evening of the 27th.

This is a great week to dust off the telescope and explore our nearest celestial neighbor.  During the late winter and early spring months Luna waxes as she climbs northward along the ecliptic, reaching a high northerly perch as she displays the best phases for exploration.  I often say that the Moon is “looked over, then overlooked” by new owners of telescopes, but our only natural satellite offers a trove of sights for those who take the time to look at her.  Her rugged terrain can be appreciated through simple spotting scopes, and she reveals more of her nearly infinite features as larger aperture instruments are employed.  Under typical atmospheric conditions, smaller telescopes are ideal for viewing the Moon, since turbulence in our atmosphere has less of a distorting effect.  My favorite instrument for Moon gazing at home is a 4-inch refractor.

During the first few evenings of the week, look for the phenomenon of “Earthshine”, where the part of Luna’s disc not directly lit by the Sun casts a ghostly blue glow.  Under clear skies you should be able to view this with the unaided eye, but a low-power view through a small telescope really brings it out.  It is best seen during the early crescent phases; after First Quarter it becomes more difficult to detect.  

Navigating around the Moon’s surface is enhanced by a good lunar atlas.  There are a number of these available for computers and smart phones as well as good old-fashioned books.  I use my 50+ year-old “Times Atlas of the Moon” at the eyepiece since lunar features don’t change much over time.  With a little practice you can build up a good memory for the Moon’s most prominent features, and before long the seemingly distant world will become a familiar place that you can visit every month.

For the first half of the week the late evening sky is unaffected by moonlight.  This will give you the opportunity to view some of the “deep sky” treats available in the winter sky.  By all accounts the Great Nebula in Orion is perhaps the easiest of these objects to find and offers a wonderful view in any telescope.  It is one of the few distant nebulae that can be seen from the city, and under dark skies it shows an amazing amount of detail.  Located some 1300 light years from Earth, it is a vast cloud of dust and gas that is the nexus of a vast stellar nursery.  From the city you can see the central regions of the nebula, with diffuse glowing gas surrounding four blue-tinted stars that form a tight grouping known as The Trapezium.  These stars pump out prodigious amounts of ultraviolet radiation that cause the surrounding gas to fluoresce.  Estimated to be some 300,000 years old, they are among the youngest stars known in the galaxy.  Larger telescopes at darker sites will show more glowing gas, crisscrossed with dark tendrils of cold interstellar dust.  Like the Moon, the nebula is often looked at, then overlooked.  It bears a long look over several nights to fully appreciate its splendor.

Venus spends the week drawing a bead on Jupiter.  Over the course of the week she advances by over one degree per day, and by the 28th she lies just over a degree west of Old Jove.  Venus will approach to half a degree from Old Jove on March 1st.  This should be a terrific sight in a low-power telescope field, with the two brightest planets in the sky sharing the same field of view along with Jupiter’s four bright Galilean moons.  You’ll get six worlds for the price of two!

Ruddy mars gets a close visit from the waxing gibbous Moon on the evening of the 28th.  The red planet is ensconced high among the stars of Taurus, the Bull and lies nearly overhead as evening twilight ends.  When Mars was at opposition last December he was bright enough to rival Jupiter.  Now he has faded, and he compares to the nearby reddish stars Aldebaran and Betelgeuse.


Commander, Naval Meteorology and Oceanography Command | 1100 Balch Blvd. | Stennis Space Center, Mississippi 39529

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