Jan. 1: The earth is at perihelion, the position in its elliptical orbit where it is nearest the sun. The distance to the sun at perihelion is about 147 ,093,000 kilometers (about 91,400,000 miles), about 5 million kilometers (3 million miles) closer to the sun than in July. This change in the earth's distance from the sun does not cause the seasons, but one of it's effects is to modify the seasons. Because perihelion occurs in the northern winter and aphelion (greatest distance) in the northern summer, the seasonal changes in the Northern Hemisphere are moderated somewhat from what they would be otherwise, while the seasons in the southern hemisphere are made more extreme. Many other factors also modify the seasons, one of the most important being the marked differences in the distribution of the oceans and continents in the Northern and Southern Hemispheres.
Jan. 4: You may see Venus low in the east this morning by looking for the waning crescent moon about 4:30. the planet rises shortly after the moon, but the sky begins to brighten in another short while. Venus is still bright, but very low, and this may be your last chance to see it as a morning star during this cycle of cofigurations.
Jan. 6: The latest sunrise of the year occurs. Sunset, by now, is already some 15 minutes later than it was in December, but the time of sunrise changes much more slowly from mid-December to mid-January.
Jan. 14: Jupiter is in conjunction with Saturn, moving from its right to its left, but remaining quite close. Of the two, Jupiter is by far the brighter. Both planets are still moving easterly (to the left) through the stars, but very slowly, and both reverse their direction within the next 10 days, to begin their retrograde (westerly) motion. Because of this fact, the faster-moving Jupiter does not drift ver far to Saturn's left before it turns around to move toward it again, catching up to it about mid-February. Use the bright star Spica (in Virgo), to the left of Jupiter and Saturn, as a "fixed" guide from which to observe the movements of the two planets over the next months. The moon is at perigee, where it is nearest the earth.
Jan. 16: The bright star near the moon tonight is Aldebaran, in Taurus. About noon (Eastern standard time) today, the moon covers Aldebaran (an occultation) over northern Canada. By tonight, the moon -- several days before full -- is to the east (left) of Aldebaran, and you can easily watch it still farther away from the star until they set several hours past midnight. This motion of the moon (reflecting its movement around the earth) is apparent its position with Aldebaran's.
Jan. 19: Saturn becomes stationary and begins its westerly (retrograde) motion relative to the stars. Jupiter is still separating slowly to Saturn's left.
Jan. 20: A penumbral lunar eclipse ( the sun is only partly obscured from the moon's surface) dims slightly the brightness of tonight's full moon. but unlike an umbral lunar eclipse, this will not make earth's shadow appear on the face of the moon.
Jan. 23: Mercury and Mars are in conjunction this evening. They are the only evening stars among the planet right now, but they are too close to the sun's position to be seen. Quite low in the west at sundown, they set before the sky darkens enough for us to see them.
Jan. 24-25: The waning gibbous moon, four days past full, is close to Jupiter and Saturn on these two evenings from the time of moonrise (about 9:30 on the 24 th, 10:30 on the 25th) on. the moon passes the two planets during daylight on the 25th; thus it shifts from right to left past them between the two evenings.
Jan. 25: Jupiter is stationary among the stars and begins its retrograde (westerly) motion, taking it to the right toward Saturn. The distance between the two will close very slowly, until Jupiter passes Saturn in mid-February.
Jan. 27: The moon, at apogee, is at its greatest distance from earth.
Feb. 1: Mercury is at its greatest distance (elongation) to the sun's left (east), leaving it above the horizon after sundown. For a week or so before and after this date, you may be able to find the planet low in the west during late twilight.
All month: There are no planets on the evenings star map this month, even though Mercury and Mars are evenings stars. While they remain above the western horizon after sundown, they are so low and so dim that it will not be easy to find them in the twilight before they set, except that Mecury will be somewhat better located during the last week of January.
The brighter planets are morning stars in January, but Venus is well past its best, dimming, rising later each day, and appearing lower in the sky at sunrise. It may still be seen low in the east during morning twilight for the first week or so in January. The only planets in good positions this month are Jupiter and Saturn.