SkyEye

The Calendar

The final eclipse of the year, an annular solar eclipse, occurs on 26 December. Unfortunately, the major meteor shower of the month, the Geminids, falls victim to moonlight.

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

After all of the excitement of last month, Mercury spends the first half of December in the morning sky before vanishing ahead of superior conjunction next month. On the penultimate day of December, Mercury undergoes its fifth aphelion of 2019.

Venus Sagittarius → Capricornus

When viewed from southern latitudes, the evening star gets as high above the western horizon as it ever will during this apparition. However, Venus continues to climb away from the Sun for northern hemisphere observers. The planet starts to brighten as its distance from Earth decreases, this in spite of the fact that the illuminated fraction of its disk is decreasing (down to 82% by the end of the month). Venus is 1.8° south of Saturn on 11 December and is occulted by the waxing crescent Moon on 29 December.

Earth and Moon

Observations of some of the meteor showers this month are hampered by moonlight. However, the Phoenicids may escape the light of the waxing crescent Moon on 2 December. Similarly, the Ursids may not suffer too badly from the light of the waning crescent Moon on 23 December.

Earth reaches it second solstice in this year on 22 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. From now until the next solstice in June 2020, days will be getting longer in the northern hemisphere and shorter in the south. Four days after solstice, the final eclipse of the year, an annular solar eclipse, takes place.

Mars Virgo → Libra

The red planet finishes a quiet year at magnitude +1.6, rising ahead of the Sun in the morning sky.

Jupiter Sagittarius

Because Jupiter reaches conjunction on 27 December, it vanishes from the evening sky early in the month. It reappears in the morning sky next year. This conjunction is particularly interesting because Jupiter actually passes behind the disk of the Sun rather than to the north or south as is usually the case. This is known as an 'anti-transit'. The lunar occultation event on the day before conjunction is not visible.

Saturn Sagittarius

Saturn is approaching conjunction in January. Therefore, it's not surprising to find it in the company of an inferior planet (a planet which is always near the Sun) this month. Venus and Saturn pair up on 11 December in the west after sunset, with the evening star much the brighter object 1.8° south of the ringed planet. The Moon also comes close on 27 December but it is no longer near enough to actually occult Saturn. In any case, this gas giant is probably lost to view before the end of the month as it disappears into the evening twilight.

Uranus Aries

Uranus is an evening sky object, setting after midnight. It is only magntude +5.7 so dark skies or a set of binoculars are necessary to observe it.

Neptune Aquarius

A small telescope is necessary to view the most distant planet in the solar system. An evening sky object which sets around midnight, it reaches east quadrature on 8 December.