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The Never Ending Cosmic Chase

by Geoff Chester, USNO Public Affairs | 17 January 2023

by Geoff Chester, USNO Public Affairs | 17 January 2023

Jupiter and Mars, 2023 January 9, imaged at the U.S. Naval Observatory
with the 30.5-cm (12-inch) f/15 Clark/Saegmüller refractor
and a ZWO ASI183MC color CMOS imager

The Moon may be glimpsed as a slender waning crescent before sunrise early in the week, then returns as a waxing crescent in the evening sky by week’s end.  New Moon occurs on the 21st at 3:53 pm Eastern Standard Time.  Early risers on the morning of the 18th can see Luna just over a degree northeast of the bright star Antares, the “heart” of Scorpius.  On the evenings of the 22nd and 23rd Luna will be near Venus and Saturn, which will have a close conjunction on the 22nd.

The January campaign for the Globe at Night citizen-science program continues this week.  The target constellation is Orion, the dominant constellation of winter nights.  The hunter sails majestically across the sky during prime evening viewing hours, crossing the meridian at 10:00 pm local time.  Orion is easy to find from virtually any place on Earth, and his distinctive outline of first- and second-magnitude stars can be easily seen from brightly lit urban areas.  Even if you live in a city center, you are encouraged to submit an observation to the Globe at Night program through their web app.  The experience will help you contribute observations throughout the year when the constellations may be a bit more difficult to see from your location.

Many of the sky’s constellations are linked in the Greco-Roman sky lore that we still use to name the star patterns that we “see”.  The origins of many of these constellations was first described by the astronomer Ptolemy, who described 48 star patterns in his pivotal work, the Almagest.  In the current sky we find the legend of Cassiopeia, Andromeda, and Perseus playing out in the northwest in the early evening.  Another legend is also at play, but this one requires the entire night to act out.  This one involves Orion and his nemesis, Scorpius.  Although Orion commands a dominant place in the sky, to the Greeks and Romans he was something of a “bit part” player.  He was a skilled and powerful hunter, but he was somewhat brash and a bit full of himself, and a half-mortal.  To that end he claimed that he could kill any creature on the planet, which angered Gaia, goddess of the Earth.  To put him in his proper place, Gaia dispatched the lowly scorpion to kill Orion, which the creature nearly did.  In the nick of time Ophiuchus, who had the gift of healing, saved Orion with an antidote to the scorpion’s venom.  Eventually Zeus placed all three of the characters in the sky, but Orion was placed opposite Scorpius so the pair would never face each other again.  

Interestingly, from a modern astronomical point of view, both constellations share a number of similarities.  Each one has as its brightest star a red supergiant, a massive evolved star that is nearing the end of its evolution.  Betelgeuse in Orion and Antares in Scorpius glow with a distinctive ruddy tint and lie well over 500 light years away.  Their outer layers have bloated out to diameters that would swallow the orbit of Mars were they in the Sun’s place in our solar system.  Each constellation also sports bright, young blue-tinted stars that share common origins in gaseous nebulae that lie nearby.  These bright blue stars give each constellation its distinctive outline that dominate the skies of winter and summer.

Venus climbs steadily into the early evening sky, becoming more prominent in the west with each passing night.  You can’t overlook the dazzling planet in the deepening twilight.  She is now the brightest planet in the sky, surpassing Jupiter, who has dominated the night for most of the past few months.  By the end of the week Venus closes in on the fainter yellow glimmer of Saturn, passing the ringed planet on the evening of the 22nd.  The two planets will be separated by less than half a degree at the time and should be visible together in the same low-power telescope field. On the evening of the 22nd the hairline crescent Moon will be about 8 degrees southwest of the pair.  On the following night Luna will be a similar distance east of Venus.

Jupiter still dominates the evening sky, but he is now well west of the meridian as evening twilight ends and will soon lose some luster to the dazzle of Venus.  The giant planet still offers several hours of telescopic viewing time starting during the fading twilight.  Almost any telescope will show the planet’s four large moons first described by Galileo in 1610.  Their constantly shifting positions from night to night allowed the Italian astronomer to measure their orbits around the planet, providing a kind of “cosmic clock” that led to the development of our modern timekeeping systems.

Mars is high overhead as evening twilight ends.  His distinctive red color is similar to the nearby bright star Aldebaran and the ruddy glow of Betelgeuse in Orion.  The red planet forms an attractive tringle with Aldebaran and the Pleiades star cluster.  Modest telescopes can still reveal his dark surface features on nights of steady air.  Other than the Moon and Mercury, Mars offers the only solid surface that we can examine from our Earthbound stage.


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

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