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Looked Over, Then Overlooked; Explore Our Nearest Neighbor

by Geoff Chester, USNO Public Affairs | 31 May 2022

by Geoff Chester, USNO Public Affairs | 31 May 2022

The Moon, imaged 2022 May 5, 01:49 UT with an Explore Scientific AR102 10.2-cm (4-inch) f/6.5 refractor, 1.6X Antares Barlow lens,
and a ZWO ASI183MC CMOS imager from Alexandria, Virginia.

The Moon returns to the evening sky this week, appearing as a slim waxing crescent in the northwestern sky as the week opens, then growing to First Quarter on June 7th at 10:48 am Eastern Daylight Time.  Luna joins the Twin Stars of Gemini, Castor and Pollux, on the evening of the 2nd.  On the 5th she forms an attractive triangle with the stars Regulus and Algieba in the constellation of Leo, the Lion.

The meteor shower that we discussed last week has come and gone, and reports from a number of observers indicated that there were some shooting stars, but definitely not a spectacle.  That said, the fact that some meteors occurred when and where they were predicted lends more credibility to the models that astronomers use to forecast such events, and thus our understanding of the science of meteors, comets, and small solar system bodies grows.  Most of the reports of sightings came from amateur astronomers, which also indicates ways that non-professional enthusiasts can help advance the science.  No special equipment was needed, just a dark sky, a pair of eyes, and patience on the part of the observers.  Hopefully the scientists will be able to better determine such future events, and when they do we’ll let you know about them.

This is a good week to turn attention back to the Moon, our closest neighbor in space.  I still have a hard time believing that this year marks the 50th anniversary of our last footsteps on Luna’s desolate surface.  In all the years that have passed since those first voyages to our natural satellite I have looked at her barren, pockmarked surface through various telescopes, always keeping in mind that people have actually been there. 

The Moon is always a treat to view with any kind of optical aid.  A steadily held pair of binoculars will reveal the ruggedness of Luna’s surface, and during the crescent phases should give you a good view of the ghostly illumination of Earthshine, which bathes the rest of the Moon’s disc in a subtle blue-tinted glow.  This is caused by sunlight reflecting off the Earth and casting its pale light onto the part of the Moon that’s not in direct illumination from the Sun.  A good spotting scope will bring the Moon into closer view, and astronomical telescopes of increasing aperture will further sharpen the view.  In recent years I have enjoyed some of my best views of the Moon with a modest 4-inch refractor telescope.  Under typical atmospheric conditions this size instrument can perform almost as well as instruments with twice the aperture.  It takes exceptionally steady air to have sharper views in larger apertures.  Much of the lunar terrain visible during the crescent phases is the result of massive asteroid impacts during the early stages of the formation of the solar system.  The first views of these relatively smooth lava plains by early astronomers and their crude optics caused them to mistake the plains for seas, and this nomenclature persists to this day.  As Luna’s phase waxes, features with names like the Sea of Fertility, Sea of Tranquillity, Sea of Nectar, and Sea of Crises come into view.  Today’s better optics show much fine detail in the lunar seas, which sport hundreds of impact craters ranging from small pits to great ringed formations with prominent central mountains.  The scale of these features is hard to grasp.  From our perch some 240,000 miles from the Moon the smallest features that can be resolved in our telescopes are comparable to Meteor Crater in Arizona.  Most of the easily visible craters are the size of the District of Columbia and larger!

Apart from the Moon, no other large members of the solar system are visible until well after midnight.  Saturn rises in the southeast at around 1:00 am, with Jupiter and Mars arriving just over an hour and a half later.  Venus crests the horizon at 4:00 am, and the whole string of our planetary neighbors should be visible by 5:00 am, as morning twilight gathers.  Saturn and Jupiter will gradually wend their ways into the evening sky as summer progresses, while Mars and Venus will be treats for late fall and winter.


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

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