SkyEye

Welcome to SkyEye, your guide to this month's celestial events.

December 2007

• All times and dates are given in Universal Time (UT).
• Nightly darkness estimates are calculated for 45° N and 30° S.
• Like total solar eclipses, lunar occultation events can be seen only from limited regions on Earth (and sometimes not at all if the occultation takes place during daylight hours). However, the Moon will appear close in the sky to its "target" for some hours either side of the actual occultation, regardless of where you are.

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 like 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. A solstice occurs on Earth 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 solstice in June, days will be getting shorter in the southern hemisphere and longer in the northern hemisphere.

Comet 17P/Holmes

Perseus
Normally invisible to the naked eye, Comet 17P/Holmes unexpectedly became many magnitudes brighter on 24 October, reaching third magnitude. Discovered by London observer Edwin Holmes on 6 November 1892, the comet has a period of approximately 7 years and spends its time between the orbits of Mars and Jupiter, last reaching perihelion in May this year. To find the comet, look for an "extra star" moving from the vicinity of alpha Persei past kappa Persei on its way to a flyby of Algol (beta Persei) next month.

Mercury

Libra -> Scorpius -> Ophiuchus -> Sagittarius
The tiny planet disappears from view as it races towards superior conjunction on 17 December. It reappears in the evening sky at the end of the month.

Venus

Virgo -> Libra
The "morning star" has put on a wonderful show for northern hemisphere observers but now Venus declines in altitude. From the south, however, the opposite is true and the bright planet climbs higher in the dawn sky. By the end of the month the "morning star" is seen equally well from both hemispheres.

Mars

Gemini
Although the red planet reaches opposition on 24 December, its elliptical orbit means that it is actually slightly closer to Earth a few days earlier. It shines brightly at -1.6 magnitude, a splendid red orb up all night. It is occulted by the Full Moon the same day it's at opposition.

Jupiter

Ophiuchus -> Sagittarius
The largest planet in the solar system is unobservable this month due to its proximity to the Sun in the sky. At conjunction on 23 December, the tilt of its orbital plane means that it actually passes behind the Sun when seen from an earthly vantage point.

Saturn

Leo
At west quadrature on the last day of last month, this is a great time to observe telescopically the interplay of shadows between the planet, its rings and its satellites. Saturn rises mid-evening.

Uranus

Aquarius
At east quadrature on 7 December, Uranus now sets before midnight.

Neptune

Capricornus
A small telescope is necessary to view the most distant planet in the solar system. The Moon occults this gas giant on 14 December.

The Celestial Sphere

Constellations are patterns of stars in the sky. The International Astronomical Union (IAU) recognises 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 summer (daylight savings) time is in effect.

For More Information...

• Consult our online glossary for non-technical explanations of many of the astronomical terms used in these pages.
• 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 your favourite amateur astronomy magazine 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 Hoag's Object in the SkyEye banner is courtesy of NASA and the Hubble Heritage Team (STScI/AURA). Discovered in 1950 by astronomer Art Hoag, this unusual ring galaxy is slightly larger than our own Milky Way. The blue ring is dominated by young, massive stars whilst the nucleus is comprised largely of older, yellower stars. Located 600 million light years away in the constellation of Serpens, Hoag's Object was photographed by the Hubble Space Telescope on 9 July 2001.

Copyright © 1995-2007 by David Harper and L.M. Stockman
Designed and maintained by Obliquity
Contact us about this page
Last modified on 30 November 2007