SkyEye

The Calendar

The Moon is busy this month, occulting the planets Mars and Uranus twice and achieving its nearest perigee of the year. Jupiter reaches perihelion on 20 January, the first time since March 2011, whilst Mars spends January moving back and forth north of the head of Taurus, the Bull.

The Solar System

The word planet is derived from the Greek word for 'wanderer'. Unlike the background stars, planets seem to move around the sky, keeping mostly to a narrow track called the ecliptic, the path of the Sun across the stars. Dwarf planets and small solar-system bodies, including comets, are not so constrained, often moving far above or below the ecliptic.

Sun Sagittarius → Capricornus

Mercury Sagittarius

Mercury makes a brief appearance in the west as the year opens but soon disappears, undergoing inferior conjunction on 7 January. It soon reappears in the morning sky in what is an excellent apparition for early risers in equatorial and southern latitudes. The tiny planet reaches a stationary point mid-month, returning to direct motion on 18 January, and reaches a greatest elongation west of 25.0° on 30 January. Look for Mercury when it's at its highest and brightest near the end of the month.

Venus Sagittarius → Capricornus → Aquarius

Venus is the evening star, appearing a little higher above the western horizon every evening. It is only 0.3° away from Saturn on 22 January; although Venus is at its minimum brightness this month, it is still far brighter than first-magnitude Saturn.

Earth and Moon

The nearly Full Moon washes out the annual display of Quadrantid meteors early in the month. Earth reaches perihelion, its closest approach to the Sun, on 4 January. The New Moon on 21 January coincides with the nearest perigee of the year; proxigean spring tides, an extreme form of a spring tide, will result. Look for the waxing gibbous Moon 2.6° south of M45, the Pleiades, on 3 January and 2.4° south of the open cluster on the penultimate day of the month. The Moon will draw closer and closer to this star cluster with each passing month, until it begins occulting the brightest member of the group in September. The waning gibbous Moon also passes 1.9° south of first-magnitude Pollux on 7 January and 2.1° north of red Antares on 18 January. Look for the comet C/2022 E3 (ZFT) from mid-month onwards as it may just reach naked-eye brightness.

Mars Taurus

Mars enters the year in retrograde, before reaching its stationary point mid-month and returning to prograde motion. It virtually retraces its steps, passing 1.7° north of the fourth-magnitude A-type variable star υ Tauri on both 2 January and 23 January, and moving 2.2° north another fourth-magnitude A-type star, κ¹ Tauri, on both 4 January and 22 January. Two lunar occultations take place this month. The first event occurs on the third day of the month, when Mars disappears behind the waxing gibbous Moon's disk. Observers in southern Africa and Madagascar should be on the look out from around 18:00 UT. The second occultation takes place on the last day of month. Beginning around 02:00 UT, the red planet vanishes behind the waxing gibbous Moon as seen from northwestern South America, Central America, Mexico, the southern United States and the Caribbean Sea. Look for Mars in the evening sky. It is at its brightest at the beginning of the year, shining at magnitude −1.2 on 1 January but dimming to −0.3 by next month.

Jupiter Pisces

Jupiter is at its maximum declination south for the year on 1 January. It reaches perihelion on 20 January, having last reached this point in 2011. Shining at magnitude −2.3, the king of the planets is an evening sky object but sets two or more hours before midnight. The waxing crescent Moon passes 1.8° south of the planet on 26 January.

Saturn Capricornus

Found just north of the fourth-magnitude variable star γ Capricorni (Nashira) as the year commences, Saturn is also at its most southerly declination for 2023. In addition, its rings are at their most open, at 13.63°. Saturn is an evening sky object, found low in the west as the skies darken, and sets during dusk by the end of the month. On 14 January, the ringed planet passes 1.4° north of another bright star in Capricornus, third-magnitude Deneb Algedi or δ Capricorni. The evening star and Saturn are 0.3° apart on 22 January but the gas giant is getting increasingly difficult to spot near the horizon as next month's conjunction approaches. The young crescent Moon passes just under 4° south of the planet the following day.

Uranus Aries

Uranus starts the year off by temporarily hiding from view. The green ice giant is occulted by the waxing gibbous Moon on 1 January, an event which is visible from northeastern United States, northern Canada, the Arctic, Greenland, Iceland, the British Isles, Scandinavia and northwestern Russia. A second lunar occultation occurs on 29 January; this is visible from the Arctic, including Alaska and Siberia. Uranus is an evening sky object, best viewed from the northern hemisphere where it doesn't set until well after midnight. The sixth-magnitude planet reaches its maximum southerly declination for the year on 21 January and two days later, returns to direct motion after having entered the year in retrograde.

Neptune Aquarius

Faint Neptune begins the year at its maximum southerly declination for 2023. An evening sky object, it sets before midnight for all latitudes. A very young crescent Moon is less than 3° south of the planet on 25 January. As always, a small telescope is necessary to view this most distant planet in the solar system.