Welcome to SkyEye, your guide to this month's celestial events. All dates are based on Universal Time (UT).
There are no eclipses this month. As seen from the Earth, the Sun is moving from the constellation Ophiuchus to the constellation Sagittarius. Solstice occurs on 22 December, ushering in winter in the northern hemisphere and summer in the southern hemisphere.
The phases of the Moon are
| Full : |
3 December
|
| Last Quarter : |
10 December
|
| New : |
18 December
|
| First Quarter : |
26 December
|
The Moon is at perigee on 2 Decemeber, at apogee on 14 December, and at perigee again on 30 December.
The Moon occults one bright planet, one minor planet, and two first-magnitude stars this month. At 6 UT on 3 December, the observers located at the very southernmost tip of South American can watch 1 Ceres disappear behind the limb of the Full Moon. Seven hours later, much of Asia and the west coast of Canada and the USA will see bright Aldebaran sliding behind the Moon's disk. Both of these events occur during night-time hours. Another night-time occultation takes place at 6 UT on 9 December with Regulus the next victim. Observers in the western part of Africa will be able to see this event. The daytime occultation of Jupiter on 25 December can be seen only from parts of the Antarctic but observers along the east coast of Canada and the USA as well as those in Europe can see Aldebaran disappear at 23 UT on 30 December.
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. This chart shows the positions of the Sun and planets at mid-month.
- Mercury
- Mercury is at inferior conjunction on 1 December and at perihelion the next day. On 11 December, the closest planet to the Sun resumes prograde motion and on 20 December, reaches greatest elongation west which will be the best time to look for it. Mercury appears just before sunrise in the constellations Libra and Ophiuchus.
- Venus
- Venus is the "evening star" seen very low in the western sky after sunset. It is gradually climbing higher in the sky but only very slowly. This brightest planet is at aphelion on 28 December and can be found in the constellations Ophiuchus and Sagittarius.
- Mars
- Like Venus, the red planet reaches aphelion this month, this time on 16 December. Mars is in the constellation Virgo so it does not rise until just after midnight.
- Jupiter
- Jupiter is at eastern quadrature on 11 December, making this a good time to observe it through a telescope in order to see interesting shadow interplay between it and its satellites. On Christmas the largest planet is occulted by the Moon but you will have to be in the Antarctic to see this event. Jupiter sets just before midnight in the constellation Aquarius.
- Saturn
- The ringed planet resumes prograde motion on 30 December. It can be observed until the early morning hours in the constellation Pisces.
- Uranus
- Uranus is just on the edge of naked-eye visibility and sets just after evening twilight. Visual aids probably will be needed to see it in the constellation Capricornus but you will have to look for it soon after the sky darkens.
- Neptune
- Neptune is falling behind Uranus after their triple conjunction in 1993. Only visible with a telescope, it can be found in the constellation Capricornus before it sets early in the evening.
- Pluto
- Pluto is currently closer to the Sun than Neptune but because it is so small and faint, a rather large telescope is always needed to see it. This smallest of the planets is in the constellation Ophiuchus, but is impossible to view this month because of its proximity to the Sun.
- Minor Planets
- The Moon occults a minor planets this month. 1 Ceres disappears behind the face of the Full Moon at 6 UT on 3 December. Only observers at the southernmost tip of South America will be able to see this event and they will need telescopes because 1 Ceres is too faint to be seen by the naked eye.
- Comets
- 21P/Giacobini-Zinner was discovered late in the year 1900 by Giacobini in France. Missed in its 1907 return, Zinner in Germany rediscovered it in 1917. It was called Comet Zinner for a short time until it was realized that it was actually Comet Giacobini. This object is the parent comet of the Draconids meteor shower which peaks this month. 21P/Giacobini-Zinner reached perihelion on 21 November.
A small comet, 21P/Giacobini-Zinner has a steeply inclined orbit (about 32°) and an eccentricity of 0.71. Its period is 6.6 years and its perihelion distance is just over 1 AU (or just outside the Earth's orbit. Visual aids will be needed to see this comet as it is expected to reach a maximum magnitude of only 9.
The comet's trajectory over the period October - December takes it through Ophiuchus, Serpens (Cauda), Aquila, Capricornus, and Aquarius. This chart shows the position of the comet every five days during this time period. The comet is travelling from west to east.
- Meteors
- There are four major meteor showers this month but the Full Moon interferes with two of them. The Phoenicids reach their peak on 6 December and the Puppid-Velids peak the following day. Unfortunately for southern observers, the light from a nearly full Moon will cause severe difficulties in viewing these displays.
The northern hemisphere fares rather better. On 14 December, the Geminids reach the peak of their display. With the New Moon only four days away, moonlight will be a problem only just before morning twilight. The Ursids peak on 22 December. The waxing crescent Moon will set before the shower really gets started.
Constellations are patterns of stars in the sky.
The International Astronomical Union (IAU) recognizes 88 different constellations. The brightest stars as seen from the Earth are easy to spot but do you know their proper names? With a set of binoculars you can look for fainter objects such as nebulae and galaxies or some of the closest stars to the Sun.
Descriptions of the sky for observers in both the northern and southern hemispheres are available for the following times this month. Subtract one hour from your local time if daylight savings time is in effect.
Northern Hemisphere : 45° N
- 1730 hours (1830 hours daylight savings)
- 1930 hours (2030 hours daylight savings)
- 2130 hours (2230 hours daylight savings)
- 2330 hours (0030 hours daylight savings)
- 0130 hours (0230 hours daylight savings)
- 0330 hours (0430 hours daylight savings)
- 0530 hours (0630 hours daylight savings)
Southern Hemisphere : 30° S
- 1730 hours (1830 hours daylight savings)
- 1930 hours (2030 hours daylight savings)
- 2130 hours (2230 hours daylight savings)
- 2330 hours (0030 hours daylight savings)
- 0130 hours (0230 hours daylight savings)
- 0330 hours (0430 hours daylight savings)
- 0530 hours (0630 hours daylight savings)
Blue moons, eclipses, the dates of Easter and much more can be found at the Interactive Astronomy Pages. For more information about the objects and events described in SkyEye, visit these astronomy-related sites.
Credits
Much of this information can be found in this month's issue of Sky & Telescope and in other fine amateur astronomy magazines available in your local bookshop. Another excellent source is the current edition of the Astronomical Calendar by Guy Ottewell and published by the Universal Workshop at Furman University.
The image of the Sun in the SkyEye banner is courtesy of the SOHO/EIT consortium. SOHO is a project of international cooperation between ESA and NASA.
Copyright 1995-98 by David Harper and L.M. Stockman
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Obliquity
Last modified on 1 December 1998
https://www.obliquity.com/skyeye/archive/1998/dec1998.html