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Looking Deep and Deeper

by Geoff Chester, USNO Public Affairs | 23 April 2024

by Geoff Chester, USNO Public Affairs | 23 April 2024

Markarian's Chain, the heart of the Coma-Virgo Galaxy Cluster
Imaged 2022 May 29 from Mollusk, Virginia with an Explore Scientific AR102
10.2-cm (4-inch) f/6.5 refractor and a ZWO ASI183MC CMOS imager.

The Moon wanes in the late evening and morning sky this week, dropping southward along the ecliptic to join the rising stars of the summer sky.  Last Quarter occurs on May 1st at 3:27 am Eastern Daylight time.  Look for Luna among the stars that form the “head” of Scorpius before dawn on the 26th.  Two mornings later she sits at the tip of the “spout” of the teapot-shaped asterism in the constellation of Sagittarius.

As the week opens the light of the Full Pink Moon washes out many of the fainter stars of the springtime sky.  During the time of evening twilight, you can spot the last of winter’s stars lingering in the western sky.  The sky’s brightest star, Sirius, should easily catch your eye, and if you follow it as it moves toward the horizon, note how Earth’s atmosphere causes it to twinkle with increased intensity.  As it moves closer to the horizon it seems to flicker through all the colors of the rainbow before setting just after 10:30 pm.  This is particularly spectacular when seen over a large body of water such as Chesapeake Bay as seen from the Eastern Shore.

One by one winter’s bright stars wink out, replaced by the more subdued luminaries of spring.  High in the south as evening twilight ends you will find the regal form of Leo, the Lion, led by the blue-white star Regulus.  Located about 79 light years from Earth, Regulus is, like many stars in the sky, a multiple star system.  A small telescope will reveal a faint companion to the north of the bright star, and each of these components is itself a spectroscopic binary system.  

Regulus sits below a semi-circle of fainter stars that together form the outline of Leo’s “head”.  This asterism is popularly called the Sickle, and its brightest star, Algieba, is one of the “showpiece” double stars in the sky.  At low power it shines with a gold-hued yellow glow, but increasing magnification reveals it to be two yellow stars of nearly equal brightness.  The pair are located about 130 light years distant and take over 500 years to complete one orbit around their center of mass. 

Leo’s hindquarters are marked by a right triangle of stars about 12 degrees east of the Sickle.  The brightest of these is Denebola, a white-tinted star some 36 light years away.

Denebola marks the western apex of an asterism known as the “Spring Triangle”.  The northernmost star in this group is the brightest star in the northern sky, Arcturus, while the southernmost is Spica, brightest star in the constellation of Virgo.  This area initially appears to be rather blank, especially under moonlit urban skies, but late in the week, if you venture to darker skies, you will find that the opposite is the case.

Sprinkled between Denebola and Arcturus is a small constellation that looks like someone spilled salt on the blackness of space.  This smattering of stars is Coma Berenices, the Hair of Queen Berenice.  She was the queen of Pharaoh Ptolemy III Euergetes, who offered her hair as a sacrifice to ensure the king’s safe return from battle.  When the tresses disappeared from the offering table, the court astronomer Conan of Samos pointed out the scattered stars to Ptolemy, and the constellation has been a part of western sky lore ever since.  The group is an actual nearby star cluster of over 50 stars located about 280 light years away.

Behind these faint stars is a relatively empty span of extragalactic space that spans some 50 million light years.  At this distance you will encounter the heart of the Coma-Virgo galaxy cluster, the nearest such aggregation of galaxies to us.  A modest telescope will reveal dozens of ghostly glimmers of soft light, each betraying the presence of hundreds of billions of stars.  Amateur astronomers call this region the Realm of the Galaxies, and hundreds are known to make up the cluster.  One of the “outliers” is our own Milky Way.

Jupiter lingers in evening twilight, setting at around 9:00 pm local time.  By mid-May he will pass behind the Sun, and we will have to wait until the fall to see him grace the evening sky again. 

Saturn greets early risers, rising at around 4:00 am in the southeastern sky.  Your best glimpse of him will be about an hour before sunrise, when the ringed planet will be about 10 degrees above the horizon.


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

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