The earth is closest to the Sun on January 2, 2024 at 8 p.m.; as our orbit is almost circular, the slight change from perihelion (.983 AU, about 91 million miles) to aphelion in July (about 94 million miles) is so small that our 23.5 degree axial tilt plays a much larger role in our modern seasons. At times, precession will shift the coldest days of winter to aphelion (for instance, the last ice ages, 11,000 years ago).
The moon is last quarter on December 3rd. The crescent moon will occult the bright red giant Antares in Scorpius for observing in the western US before sunrise on January 8. The brilliant planet Venus will be just NE of the pair. The next morning, it sill lie south of fainter Mercury in the twilight. Look closely with binocs and you may also spot Mars coming out from behind the Sun into the dawn. New Moon is January 11th; three more new moons to the April 8th total solar eclipse. More on that later, of course. The slender crescent lies below Saturn on January 13th, and above it on the 14th. The first quarter moon is on January 17th, and it passes below Jupiter the following evening. The full moon, The Snow moon, is on January 25th.
Mercury is in the dawn most of January, to the lower left of Venus. It is at greatest western elongation, 24 degrees in front of the rising Sun, on January 12th, and heads back to the far side of the Sun. It merges with Mars in the dawn on January 27th, only .3 degrees above the Red Planet. Use binoculars about 40 minutes before sunrise. By month’s end, Mercury is lost in Sun’s glare, and Venus too is getting lower and lower in the dawn; it will pass behind the Sun by Spring. Mars will slowly climb high in the dawn for the next several months.
Jupiter is well up in the southern sky at sunset, well placed for telescopic observations of its four Galilean moons and famed Great Red Spot. Saturn is low in the Southwest in Aquarius by month’s end, and will be lost in the Suns glare by the end of February.
The constellation Cassiopeia makes a striking W in the NW. Her daughter, Andromeda, starts with the NE corner star of Pegasus’’ Square, and goes NE with two more bright stars in a row. It is from the middle star, beta Andromeda, that we proceed about a quarter the way to the top star in the W of Cassiopeia, and look for a faint blur with the naked eye. M-31, the Andromeda Galaxy, is the most distant object visible with the naked eye, lying about 2.5 million light years distant. It is accompanied in small telescopes by companion galaxies M-32 and M-110; we also know of about a dozen smaller satellites gravitationally bound to M-31.
Overhead is Andromeda’s hero, Perseus. Between him and Cassiopeia is the fine Double Cluster, faintly visible with the naked eye and two fine binocular objects in the same field. Perseus contains the famed eclipsing binary star Algol, where the Arabs imagined the eye of the gorgon Medusa would lie. It fades to a third its normal brightness for six out of every 70 hours, as a larger but cooler orange giant covers about 80% of the smaller but hotter and thus brighter companion as seen from Earth.
Look at Perseus’ feet for the famed Pleiades cluster; they lie about 400 light-years distant, and over 250 stars are members of this fine group. East of the seven sisters is the V of stars marking the face of Taurus the Bull, with bright orange Aldebaran as his eye. The V of stars is the Hyades cluster, older than the blue Pleaides, but about half their distance.
Yellow Capella, a giant star the same temperature and color as our much smaller Sun, dominates the overhead sky. It is part of the pentagon on stars making up Auriga, the Charioteer (think Ben Hur). Several nice binocular Messier open clusters are found in the winter milky way here. East of Auriga, the twins, Castor and Pollux highlight the Gemini. You can associate the pair with Jason and the Golden Fleece legend, for they were the first two Argonauts to sign up on his crew.
South of Gemini, Orion is the most familiar winter constellation, dominating the eastern sky at dusk. The reddish supergiant Betelguese marks his eastern shoulder, while blue-white supergiant Rigel stands opposite on his west knee. As noted last month, on December 11th, the asteroid Leona passed in front of the huge red giant, and as predicted, the 300 mile wide rock did not quite cover the whole surface of the largest star in the sky (except for the Sun, of course) as seen from earth.
While the occultation was not seen in the United States, on the other side of the Atlantic, dozens of observers made detailed recordings to the fading of the star from first to third magnitude (about 1/3 its original brightness) for ten seconds or less! Just south of the belt, hanging like a sword downward, is M-42, the Great Nebula of Orion, an outstanding binocular and telescopic stellar nursery. It is part of a huge spiral arm gas cloud, with active star birth all over the place. You should be able to glimpse this stellar birthplace as a faint blur with just your naked eyes, and the larger your binoculars or telescope, the better the view becomes.
While M-42 is a emission nebulae, shining reddish from the ionization of its hydrogen gas by hot young stars forming inside it, the famed Horsehead south of the belt of Orion is a dark nebula, a dust cloud lying in front of the red glowing background hydrogen. Just north of it is the much easier Flame Nebula, in the same field of view as Mintaka, the eastern member of the belt. It is also an emission nebula. But the blue color around Mintaka is a reflection nebula, scattering the shorter wavelengths off the interstellar dust, just as small particles in our atmosphere scatter shorter blue waves best, making our sky blue. This is called Rayleigh scattering.
Enjoy such star spectacles while you can. This whole Orion molecular cloud is rich in much dust as well as hydrogen to churn out new, very luminous blue stars like the ones that dominate the naked eye constellation. The horsehead’s dust is collapsing into protostars, and their heat and light will soon destroy the famed profile. Even the flame is not everlasting, but its shape and brightness will vary as new stars are born in the dark "wick" to expand the flames still brighter. M-42 also is constantly changing!
Last but certainly not least, in the east rise the hunter’s two faithful companions, Canis major and minor. Procyon is the bright star in the little dog, and rises minutes before Sirius, the brightest star in the sky. Sirius dominates the SE sky by 7 PM, and as it rises, the turbulent winter air causes it to sparkle with shafts of spectral fire. Beautiful as the twinkling appears to the naked eye, for astronomers this means the image is blurry; only in space can we truly see "clearly now". At 8 light years distance, Sirius is the closest star we can easily see with the naked eye. Below Sirius in binoculars is another fine open cluster, M-41, a fitting dessert for New Year’s sky feast.
