SkyEye

The Calendar

Earth not only finally gets a total solar eclipse this year but it occurs during the excellent Geminid meteor shower. Jupiter and Saturn experience a 'Great Conjunction' on 21 December, coming to within 0.1° of each other. Don't miss it as the next one is twenty years away.

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 Ophiuchus → Sagittarius

Although Ophiuchus is not a member of the zodiac, the ecliptic passes through it.

Mercury Libra → Scorpius → Ophiuchus → Sagittarius

Mercury is already low to the eastern horizon at the beginning of the month and is soon lost to view. A lunar occultation occurs on 14 December but both planet and the New Moon are too close to the Sun for the event to be visible. Mercury reaches superior conjunction on 20 December and returns to the evening sky at the end of the month. The tiny planet is quite bright throughout the month, starting December at magnitude −0.8.

Venus Libra → Scorpius → Ophiuchus

The morning star is occulted by the waning crescent Moon on 12 December. This event is visible from northeastern Asia and northern Alaska from around 19:00 UT. Venus continues to lose altitude in the east; this morning apparition will end next March. When viewed through a telescope, the waxing gibbous disk is getting increasingly small in diameter but the illuminated fraction is growing, from 89% ot 94%. This balance between illumination and diameter means that Venus remains at magnitude −4.0 until the end of the year.

Earth and Moon

Both inferior planets are occulted by the Moon this month but only the Venus occultation on 12 December may be visible. The final eclipse of the year occurs on 14 December when the New Moon totally obscures the face of the Sun. This event happens around the same time as the Geminid meteor shower which means dark moonless skies for watching shooting stars. The Phoenicid and π Puppid meteor showers early in the month are not so lucky and observations of these meteors are hampered by moonlight. The First Quarter Moon should set early enough to allow the Ursids to shine in the early morning hours later in the month.

Earth reaches it second solstice in this year on 21 December. The word solstice means 'sun stands still' so that on this day, the solar declination reaches an extreme. In this case, the Sun appears directly over the Tropic of Capricorn in the southern hemisphere.

Mars Pisces

Mars returns to the north side of the ecliptic when it passes through its ascending node on the second day of the month. The red planet, fading slightly from magnitude −1.1 to −0.2, is becoming increasingly gibbous-looking through a telescope as opposition recedes. Mars is an evening sky object, best viewed from northern latitudes where it doesn't set until after midnight. Astronomers in the southern hemisphere should look for the planet as soon as the sky gets dark as Mars sets much earlier for them.

Jupiter Sagittarius → Capricornus

Jupiter is found in the western part of the sky after sunset. The thin waxing crescent Moon passes the bright planet on 17 December but the main event is the conjunction of Jupiter and Saturn on 21 December. On this date the two planets will be only 0.1° apart some 30° away from the Sun. This event is sometimes referred to as a 'Great Conjunction'; the last time it happened was on 31 May 2000 when the two planets were 1.2° apart and only 17° away from the Sun, and the next such occurence won't be until 5 November 2040 when Jupiter and Saturn will again be 1.2° apart and 25° from the Sun.

Saturn Sagittarius → Capricornus

Jupiter has been slowly closing on the position of Saturn all year and the 'Great Conjunction' finally takes place in the western sky on 21 December when the two planets are within 0.1° of each other. See the description for Jupiter above for more details.

Uranus Aries

Faint Uranus is visible in the evening sky, most easily viewed from northern latitudes.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. Neptune reaches east quadrature on 9 December in the evening sky.