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December 2025 Observing Guide

  • Andrew Wood
  • 15 hours ago
  • 5 min read

Updated: 9 hours ago

The following describes objects in our night sky for December and is especially written for beginning observers.


Moon Phases

The Deep Sky Objects described later should be visible with the Moon present, although they will be better seen at times when the Moon is not visible. Still, don’t be put off by the Moon if the sky is clear. See what you can and try again on a moonless night.


December starts with the 10-day old Waxing Moon, becoming more gibbous each day until…


Dec 5: Full Moon – rising around sunset. Afterwards, it wanes through gibbous phases toward…


Dec 12: Last Quarter – rising around midnight. Afterwards, it wanes through crescent phases toward…


Dec 20: New Moon – rising and setting with the Sun. No moon visible all night. Afterwards, it waxes through crescent phases toward…


Dec 28: First Quarter - the Moon rises about midday and sets about midnight.


Planets

The gas giants are the only bright planets in telescope range this month. They are the best of the planets to observe, however.


Jupiter will be about 10° above the eastern horizon at 11PM mid-month, rising earlier each night as it approaches opposition in January. It is presenting a large disc of about 45” and a magnitude of -2.6. Now is a good time to start observing our largest planet, as it will be increasingly prominent in the coming months. The zones, belts and the Great Red Spot on the planet’s surface, and the four Galilean moons as they circle the planet make Jupiter great to observe.


As Jupiter begins to dominate the east eastern sky from late December, Saturn is at its highest as the sun sets, making it easily visible in the west for several hours afterwards. At present, the planet’s rings from our Earthly perspective appear edge-on. They will gradually widen for the next seven years, and the edge-on perspective will not occur again until 2038. When the atmosphere is steady – good “seeing” – large aperture telescopes can show some features on the surface of Saturn, especially when the rings are edge-on as they are now. At magnitude 8, the satellite Titan is visible in any telescope. Despite its distance, there are more moons of Saturn visible than Jupiter. A dark sky and large aperture will help see them as they are, however, much fainter than Titan and Jupiter’s four Galilean moons.


Deep Sky Objects

With the shorter summer days and Daylight-Saving Time, darkness does not set in until nearly 10PM, at which time, the Southern Cross is low on the southern horizon. Much higher, though, still looking south, lie the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (LMC). These can be seen with the naked eye in a decent suburban sky, though being away from city lights is better. Mid-month corresponds with moonless skies this month, which makes viewing better.


The image below was taken with a dSLR camera [20 second exposure at ISO 1600, F4]. At top right is the star Achernar, and at lower left the area around Eta Carina. The LMC and SMC along with other deep sky objects, are numbered. The descriptions of these objects follow.


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  1. LMC: Appearing as a faint, hazy patch to the naked eye, and located about 160,000 light-years from Earth, the LMC is a satellite galaxy of the Milky Way and is rich in star clusters and nebulae.


  1. SMC: Similar in appearance but smaller than the LMC, the SMC lies approximately 200,000 light-years from Earth. Like its larger counterpart, it is also a satellite galaxy of the Milky Way. Unlike the LMC, The SMC has been designated an NGC catalogue number – NGC 292.


  1. 47 Tucanae, also known as NGC 104. Visible to the naked eye if the sky is dark enough, and easily visible in binoculars. This is one of the brightest and largest globular clusters in the night sky, appearing as a dense, shimmering sphere of stars near the SMC. Located about 16,700 light-years away, 47 Tucanae contains hundreds of thousands of stars tightly packed together. Telescopes, especially of larger apertures and at high magnification, resolve the cluster into individual stars. It’s a spectacular site.


  1. NGC 362 is another impressive globular cluster, situated close to the SMC and not far from 47 Tucanae. Located approximately 27,700 light-years from Earth, NGC 362 is slightly fainter and more compact than 47 Tucanae but still visible with binoculars or a small telescope under dark conditions. Once again, a telescope resolves individual stars.


  1. Tarantula Nebula, also known as NGC 2070 and 47 Doradus. The LMC is a star-forming region, and the most notable example within the galaxy is the Tarantula Nebula. The nebula contains a rich concentration of young, massive stars and star clusters. Visible through binoculars just off the main body of the LMC, a telescope reveals its complex nature, especially if a nebula filter is used.


These are the brightest objects in and around the LMC and SMC, easily visible. Both galaxies contain many more objects. Navigating around them requires a good star atlas and maybe a Go-To telescope.


Some Useful Terms

Aperture is the diameter of the lens or mirror that the telescope uses to collect light.

Magnitude is how bright an object is. Smaller Numbers have Brighter Magnitudes – e.g. Magnitude 1 is brighter than magnitude 2. A very dark sky will allow stars as faint as magnitude 6 to be visible. Very bright objects – bright stars and planets, the Moon and Sun, have negative magnitudes.


Magnification, or Power, is calculated by dividing the focal length of a telescope by the focal length of the eyepiece being used. The 100mm refracting telescope in the Observatory has a focal length of 550mm. The 42mm eyepiece that is in the telescope when you enter the Observatory yields a magnitude of 550/42 = 13. This gives a very wide field of view to locate the object. Exchanging for eyepieces with shorter focal lengths increases the magnification, enabling more detail to be seen. An 8mm eyepiece in our telescope will give nearly 70X magnification.


M stands for objects in the Messier Catalogue of 110 objects. This was one of the earliest lists of deep sky objects compiled in the 1700s. Most of the objects in this catalogue will also have an NGC number.


NGC stands for New General Catalogue. All Deep Sky Objects will have a catalogue number, of which the NGC is the most well-known, with more than 7,000 objects. Many brighter, more well-known objects have names such as Jewel Box, Blue Planetary etc. All of these will also have a number in one of the many astronomical catalogues.


FOR THOSE NEW TO AMATEUR ASTRONOMY

I strongly advise that you purchase or borrow books, or read online sites, devoted to teaching basic Astronomy. Teach yourself about:


  • Different types of telescopes

  • Aperture and Focal Length

  • Magnification

  • Eyepieces, Barlow lenses and filters

  • Navigating the night sky

    • Planispheres

    • Star Atlases

    • Right Ascension and Declination

  • Deep Sky Objects – clusters, nebulae and galaxies


Andrew Wood


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