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The Pleiades' Half Sisters

by Geoff Chester, USNO Public Affairs | 07 November 2023

by Geoff Chester, USNO Public Affairs | 07 November 2023

The Pleiades and the Hyades, imaged 2020 January 2 from Mollusk, Virginia
with a Canon EOS Rebel SL2 DSLR and an Omegon Mini Track LX2 mechanical star tracker

The Moon greets early risers as the week begins, waning through her crescent phases before New Moon, which occurs on the 13th at 4:27 am Eastern Standard Time.  During the week Luna has a close conjunction with brilliant Venus before dawn on the 9th.  This should be a great photo opportunity as the two objects will be just one degree apart.  Look for the very slender lunar crescent to the east of the rising star Spica in the gathering morning twilight of the 11th.  

The November campaign for the citizen-science Globe at Night program is under way this week.  The goal of the program is to document the brightness of the night sky over as many locations around the world as is possible.  Sponsored by the National Science Foundation and DarkSky International, the program also seeks to raise awareness of our rapidly-vanishing dark sky caused by light pollution.  To participate, all you need to do is find a place where you have an unobstructed view of the sky and a target constellation to compare with star brightness charts on the website.  

This month’s target constellation is Pegasus, the mythical flying horse of ancient Greek lore.  The constellation’s main stars form a large square that you will find high in the south at 8:00 pm local time.  The “Great Square” should be visible to urban sky gazers, and as you move farther afield to darker sites a number of fainter stars should appear within the Square’s bounds.  From truly dark areas over a dozen faint stars dot the sky within the square.

Last week we discussed the Pleiades star cluster, which, thanks to the return to Standard Time, may now be seen high in the east at 10:00 pm local time.  In depictions from classical star atlases, the diminutive group is usually pictured on the back of Taurus, the Bull, whose brightest star Aldebaran leads the bright stars of the Great Winter Circle into the sky.  From a dark location you can see a prominent “V”-shaped group of stars with Aldebaran marking the east tine of the V.  Urban sky watchers can easily see this group with binoculars, and it doesn’t take a huge leap of imagination to see the outline of a bull’s face with Aldebaran shining like a fiery-red eye.  The V-shaped group is indeed another star cluster, somewhat more scattered and closer to us than the Pleiades.  In mythology these stars represented the Hyades, half-sisters of the Pleiades.  Even more so than their half-sisters, the Hyades were associated with wet and stormy weather, perhaps because they are more difficult to see behind the high clouds associated with approaching storms.  They are mentioned as omens of bad weather by the ancient authors Pliny and Homer, and by more modern writers like Tennyson and H.P. Lovecraft.

The Hyades have about 20 stars visible to the naked eye under dark skies, and a modest amateur telescope will show some 250 members.  The cluster is about 150 light years distant, and it is gradually moving away from us.  Proper motion studies show its member stars converging on a location just east of the star Betelgeuse in Orion in a few million years.

Although it appears to be a cluster member, the star Aldebaran is actually a “foreground” object.  It is located about 65 light years away, and in a few thousand years will lose its place as the Bull’s red eye.

Saturn now crosses the meridian at around 7:00 pm thanks to the change to Standard Time.  This is the best time to view the ringed planet for Northern Hemisphere residents.  Here in Washington Saturn reaches an altitude of just under 40 degrees above the southern horizon, and you will have about two hours of good viewing time through the telescope before he slips into denser air.  His enigmatic rings are tipped about 12 degrees to our line of sight.  They will gradually close up and disappear when they present their next edge-on view in 2025.

Jupiter quickly replaces Saturn as the most prominent planet in the night.  Old Jove appears low in the east shortly after sunset and crosses the meridian at around 11:30 pm.  If there is one planet worth watching for a couple of hours, it is Jupiter.  In modest telescopes you can see changes in the planet’s streaky cloud patterns, or watch the pink hue of the Great Red Spot rotate across his disc.  When any of the four bright Galilean moons are near the planet, you can watch their positions change in a matter of minutes.  

Venus and the Moon entertain early risers for several days this week.  They share the celestial limelight before dawn from the 8th to the 11th, with their closest approach occurring on the 9th.  Look for Earthshine on Luna’s disc if you catch the pair before the start of morning twilight. 


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

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