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The Moon Returns, and a Grand Telescope is 150!

by Geoff Chester, USNO Public Affairs | 14 November 2023

by Geoff Chester, USNO Public Affairs | 14 November 2023

Jupiter, imaged 2016 April 6, 02:48 UT
with the 66-cm (26-inch) "Great Equatorial" refractor at the
U.S. Naval Observatory, Washington, DC

The Moon returns to the evening sky this week, waxing through her crescent phases before reaching First Quarter, which occurs on the 20th at 5:50 am Eastern Standard Time.  Look for Luna’s skinny crescent low on the southwestern horizon on the evening of the 15th.  Over the course of the week, she begins a northward climb through the dim autumnal constellations.  The Moon passes five degrees southeast of golden Saturn on the evening of the 20th.

The night of the 17th-18th is the predicted peak time for one of the most notorious of meteor showers.  The Leonids are the detritus of a comet, 55P/Tempel-Tuttle, which circles the Sun every 33 years.  The comet was co-discovered from the Naval Observatory on January 5, 1866 by Horace P. Tuttle, a U.S. Navy paymaster and astronomer, about two weeks after it was initially spotted in France by the German astronomer Wilhelm Tempel.  Their discovery observations identified the comet’s 33-year period, and it was later matched to comets seen in 1366 and 1699.

This shower normally has relatively low activity, but occasionally it produces incredible meteor “storms”.  Such was the case in 1833, when thousands of meteors seemed to rain down over the U.S., prompting widespread fears of the end of the world.  Among the witnesses of this spectacle was a young Abraham Lincoln.  In 1966 observers in California saw shower rates in excess of 100,000 meteors per hour.  Enhanced showers were seen in 1999, 2001, and 2002.  I observed the 2001 shower from a park in Alexandria, and gave up counting meteors after seeing some 400 in half an hour.

Due to its very unpredictability, the shower and its parent meteoroid stream has been extensively studied.  While a “storm” isn’t expected this year, some models predict that Earth will cross a stream of comet particles ejected in its 1733 return, producing upwards of 50 swift meteors per hour for observers in dark locations.  The meteors appear to “radiate” from the constellation of Leo, the Lion, which will be high in the south as morning twilight begins.  The waxing crescent Moon will set long before Leo rises.

On November 12, 1873, a small group of U.S. Naval Observatory astronomers first peered through the eyepiece of the world’s largest refractor telescope, the 26-inch (66-cm) aperture “Great Equatorial”, designed and built by the firm of Alvan Clark & Sons of Cambridge, Massachusetts.  Less than four years later the great telescope revealed the two moons of Mars, Phobos and Deimos, to astronomer Asaph Hall, a discovery ranked as one of the most important astronomical events of the 19th Century.  150 years later, the telescope continues to provide state-of-the-art astronomical data for the benefit of the Navy, the Department of Defense, and the scientific community.

Over the years, the telescope has been used for observations of the faint moons of the outer planets and the astrometric properties of double stars.  As new observing techniques such as photography and digital imaging replaced the practiced eyes of astronomers, the great telescope evolved to adapt to the changes.  It is the oldest continuously-operating research-grade telescope on the planet.

Today the 26-inch telescope, still fondly called the “Great Equatorial”, operates entirely under computer control, automating almost the entire observing process.  Its primary mission is determining the separations and position angles of double stars, a task for which it is ideally suited.  Nearly 55,000 measurements of these stars have been secured with the telescope, more than any other telescope in the world.

Saturn may be found in the south as evening twilight ends.  He occupies a relatively sparse region of the sky as he slowly drifts eastward against the faint stars of Aquarius.  His only “competition” is the lonely first-magnitude star Fomalhaut, located about 20 degrees southeast of the ringed planet.  Take a good telescopic view of Saturn early in the evening; by 10:00 pm he is settling toward the southwest horizon. 

Jupiter is now the dominant object in the evening sky.  You can spot the giant planet in the east shortly after sunset, and by 8:00 pm local time you should be able to get a clear view of him through the telescope.  Since the Old Jove rotates once in less than of hours, you can see noticeable changes in his cloud belts, especially of the Great Red Spot is visible.  You can also see the orbital motion of the Galilean moons, especially when two of them appear close to each other. 

Venus spends the week dominating the pre-dawn sky.  She is currently drifting eastward among the stars of the sprawling constellation of Virgo.  On the mornings of the 17th and 18th Venus will be just over a degree from the second-magnitude star Porrima, Virgo’s second-brightest star.  If you have a telescope, Porrima is a close binary star system with a period of 168 years.  It is one of the few binary stars whose components change their positions from year to year.


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

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