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The Action is in the Evening Sky

by Geoff Chester, USNO Public Affairs | 12 March 2024

by Geoff Chester, USNO Public Affairs | 12 March 2024

Messier 42, the Great Orion Nebula, and NGC 1977, the Running Man Nebula
Composite image made on 2024 February 4 at Sky Meadows State Park, Paris, Virginia
and February 6 at Alexandria, Virginia with a ZWO Seestar S50 "Smart Telescope"

The Moon waxes as she climbs northward along the ecliptic, passing over the stars of the Great Winter Circle.  First Quarter occurs on the 17th at 12:11 am Eastern Daylight Time.  Luna may be found just north of bright Jupiter on the evening of the 13th.  On the following evening she lies just west of the Pleiades star cluster.  She ends the week flirting with Castor and Pollux, the Twin Stars of Gemini.

This is another good week to get to know our nearest celestial neighbor.  Exploration of the Moon can be done with a pair of binoculars, which will begin to reveal the battered ancient terrain of this airless world.  A small telescope, though, will start to show just how desolate the lunar landscape is.  A four-inch aperture should show details down to about a mile across at the Moon’s distance, and as the week progresses the terminator line gradually unveils new features for all to enjoy.

The vernal equinox occurs on the 19th at 11:06 pm EDT.  This is the moment when the center of the Sun’s disc reaches an ecliptic longitude of zero degrees, beginning the astronomical season of spring.  It is also the time when the Sun crosses the celestial equator and moves into the northern hemisphere of the sky.

The term “equinox” implies the concept of “equal night”, when day and night are exactly 12 hours in duration.  If the Sun were a point source of light, this would be the case on the day of the equinox.  However, in reality, sunrise is defined as the moment when the Sun’s upper limb breaks the eastern horizon, while sunset occurs when the last vestige of the limb vanishes in the west.  Thus the actual date for 12 hours of daylight and darkness in Washington this year is March 16, when Old Sol rises at 7:19 am EDT and sets at 7:19 pm.

Hopefully by now you have adjusted to the switch to Daylight Time.  As an astronomer, I’m not too thrilled with the change, since by mid-summer evening twilight doesn’t end until after 10:30 pm, but for the casual stargazer it gives the winter constellations one last chance to capture a view of the night’s brightest constellations.  With sunsets now occurring at around 7:20 pm, you can easily spot the stars of Orion and his cohorts by 8:20 pm.  The winter stars dominate the western sky through the evening hours, holding back the spring constellations for a few more weeks.

Take advantage of this reprieve and the gradually warming evenings to spend some time star-hopping around Orion.  The constellation has something for observers of any skill level and optical aid.  To the unaided eye, most of the Hunter’s stars are blue in tint with the exception of ruddy Betelgeuse, and it doesn’t take a great leap of the imagination to understand why this constellation has roots in the sky lore of cultures past and present.  Scanning the constellation with binoculars brings out the colors of the stars and reveals a number of bright star clusters and a mass of fuzzy light in the asterism known as The Sword, which hangs just below Orion’s distinctive belt.  For the telescope owner, the Sword comes alive with the swirling gas clouds of the Great Nebula, which holds the tight grouping of stars known as the Trapezium at its heart.  The nebula is flanked to the north and south by loose clusters of blue-tinged stars embedded in faint, gauze-like nebulosity.

Jupiter now appears halfway from the western horizon to the zenith as evening twilight fades to night.  You can still get a decent view of the giant planet in the telescope, but his apparent diameter is now about 75 percent of its size when the planet was at opposition.  In addition, as Old Jove gets lower in the sky, Earth’s atmosphere adds turbulence to the view, so the best time to give him a look is shortly after sunset.  Once he has set, though, bright planets are very hard to find for the rest of the night.

If you have a clear view to the western horizon, look for the elusive planet Mercury late in the week.  The fleet planet is beginning his best evening apparition of the year, and he should remain visible through the end of the month.  Look for him about five degrees above the southwest horizon on the evening of the 16th.  He will climb about a degree higher each evening before reaching his greatest elongation from the Sun on the 24th.


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

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