The final month of 2023 provides stargazers with beautiful celestial events to observe in the night sky. At the start of December, Mercury reaches its greatest eastern elongation from the Sun on the 4th. This gives observers a great opportunity to safely view our closest neighbor.

Later, on the 14th, the Geminids meteor shower reaches its peak displaying upwards of 150 meteors per hour. The following night, the Running Man Nebula is well placed in the sky reaching its highest point.

Also, Asteroid Vesta reaches opposition on the 21st and the Ursids meteor shower peaks on the 22nd.

December finishes off with the Full Cold Moon on the 26th and nice placements in the sky of NGC 2232 on the 29th and the Rosette Nebula on the 30th.

(Looking to review last month's astronomy events? View November 2023)

Our highlighted list of astronomy events for December serves as your reference for key celestial targets to plan for.

8 Astronomical Events in December 2023:

Mercury at greatest eastern elongation - 12/4
Geminids meteor shower peak - 12/14
The Running Man Nebula is well placed - 12/15
Asteroid 4 Vesta at opposition - 12/21
Ursids meteor shower peak - 12/22
Full Cold Moon - 12/26
The cluster NGC 2232 is well placed - 12/29
The Rosette Nebula is well placed - 12/30

First, a few technical terms to know:

Magnitude - Magnitude is the measure of an object's brightness. The lower the number the brighter the object. Conversely, the higher the number the fainter the object (ex. a magnitude -7.2 object is brighter than a magnitude +3.6 object). Without optical assistance, the naked eye can see a celestial object as dim as roughly magnitude +6.0.

Right Ascension - Right ascension is the celestial equivalent of geographic longitude. It is measured from the Sun's position during March Equinox at 00h00m00s (h=hours, m=minutes, s=seconds). This measurement increases towards the east until it completes a full circle at 24h00m00s.

Declination - Declination is the celestial equivalent of geographic latitude. It is measured northward or southward of the celestial equator as degrees (°), minutes(') and seconds ("). For example, the celestial equator has a declination of 0°0'0", the north celestial pole has a declination of +90°0'0" and the south celestial pole has a declination of -90°0'0".

AU (astronomical unit) - AU is a unit of length that measures the distance from the Earth to the Sun.

Angular Size - Angular size refers to a celestial object's apparent size as seen from an observer on Earth. It is measured in arcminutes(') and arcseconds(").

Astronomy events to mark on your December 2023 calendar:

December 4th - Mercury at greatest eastern elongation

Mercury

Mercury will reach its widest separation from the Sun on Monday, December 4th. The planet will be positioned 21° east of the Sun shining at magnitude -0.5 in the Sagittarius constellation.

This is referred to as its greatest eastern elongation. These wide separation moments occur roughly once every 3-4 months.

Due to Mercury's close proximity to the Sun, the planet is often difficult to safely observe. Therefore, for stargazers, the exact dates of Mercury's greatest eastern and western elongation are significant moments that provide an opportunity for optimal observations.

At its greatest eastern elongation, Mercury will be visible in early evening twilight.

Mercury at greatest eastern elongation

Magnitude: -0.5
Right ascension: 18h13m40s
Declination: 25°36'S
Angular size: 6.7"

December 14th - Geminids meteor shower peak

Geminids

The Geminids meteor shower is active from November 19th to December 24th. It reaches its peak on Thursday, December 14th. Its radiant point, the area from which the shower appears to emanate, is positioned in the Gemini constellation around right ascension 07h20m and declination 33°N.

According to the American Meteor Society, this meteor shower's ZHR will be approximately 150 meteors per hour. ZHR is an abbreviation for Zenithal Hourly Rate and is defined as the hourly rate at which a meteor shower produces with a clear, dark sky, and with the radiant at the zenith (highest point directly above the observer).

The parent body responsible for creating the Geminids shower is asteroid 3200 Phaethon.

Tips for viewing meteor showers:

Do not direct your gaze solely at the radiant point. The closer a meteor is in proximity to its radiant point, the more difficult it is to see because of its shorter trail.
Position yourself in a dark, secluded location away from light pollution and bright city lights.
Allow for up to 30 minutes for your eyes to properly adjust to the dark environment.
Make sure to dress appropriately for the weather.
Bring a comfortable lawn chair in which you can recline or a blanket to lie back on.
Try to observe as wide an area of the sky as possible. The broader your view of the sky, the greater the chance of catching a glimpse of a meteor whizzing by.

December 15th - The Running Man Nebula is well placed

Running Man Nebula

The Running Man Nebula, also known as NGC 1977, will reach its highest point in the sky at around midnight local time on Friday, December 15th.

This reflection nebula is not visible to the naked eye. However, the use of a small aperture telescope or a pair of binoculars will provide the best views. This celestial object can be seen at latitudes between 65°N and 74°S.

NGC 1977 is the northernmost part of the asterism known as Orion's Sword, lying 0.6° north of the Orion Nebula.

Running Man Nebula on 12/15

Magnitude: +6.6
Right ascension: 05h35m10s
Declination: 4°50'S
Constellation: Orion

December 21st - Asteroid 4 Vesta at opposition

Vesta

On Thursday, December 21st, Asteroid 4 Vesta will be at opposition and will reach its highest point in the sky around midnight local time.

A celestial object "at opposition" refers to its 180° position opposite to the Sun. During this alignment Vesta will rise at around sunset, and set at around sunrise.

Vesta will be at a distance of 1.583 AU, shining at magnitude +6.4 in the Orion constellation. A moderate aperture telescope or a pair of binoculars should be used to help you properly observe this asteroid.

Vesta at opposition

Magnitude: +6.4
Right ascension: 05h56m50s
Declination: 20°32'N
Constellation: Orion

December 22nd - Ursids meteor shower peak

Ursids

The Ursids meteor shower is active from December 13th to December 24th. It reaches its peak on Friday, December 22nd. Its radiant point, the area from which the shower appears to emanate, is positioned in the Ursa Minor constellation around right ascension 14h20m and declination 75°N.

According to the American Meteor Society, this meteor shower's ZHR will be approximately 10 meteors per hour. ZHR is an abbreviation for Zenithal Hourly Rate and is defined as the hourly rate at which a meteor shower produces with a clear, dark sky, and with the radiant at the zenith (highest point directly above the observer).

The parent body responsible for creating the Ursids shower is comet 8P/Tuttle.

December 26th - Full Moon | Cold Moon

Hunters Moon

On Tuesday, December 26th, the Moon will reach the full phase of its 29.5 day lunar cycle rising at around dusk and setting at around dawn. This astronomical event occurs each time the Moon's ecliptic longitude appears 180° away from the Sun's ecliptic longitude.

According to the Farmers' Almanac, traditionally the Full Moon that occurs after the Winter Solstice is referred to as the Cold Moon. It is believed that the name originates from the frigid weather conditions of this time of year.

Full Cold Moon

Right ascension: 06h20m50s
Declination: 28°08'N
Constellation: Auriga
Angular size: 30'29"
Distance from Earth: 391,000 km (242,956 miles)

December 29th - The cluster NGC 2232 is well placed

NGC 2232

The open star cluster NGC 2232 will reach its highest point in the sky at around midnight local time on Friday, December 29th.

At magnitude +4.2, this cluster is difficult to see with the naked eye except from a dark site. However, the use of a small aperture telescope or a pair of binoculars will provide better views.

NGC 2232 is one of the nearest open star clusters to the Sun and is located close to the Orion Nebula.

NGC 2232 on 12/29

Magnitude: +4.2
Right ascension: 06h28m00s
Declination: 4°50'S
Constellation: Monoceros

December 30th - The Rosette Nebula is well placed

Rosette Nebula

The Rosette Nebula, also known as Caldwell 49, will reach its highest point in the sky at around midnight local time on Saturday, December 30th.

At magnitude +4.3, this nebula is difficult to see with the naked eye except from a dark site. However, the use of a small aperture telescope or a pair of binoculars will provide better views.

The Rosette Nebula has been noted to be having a shape reminiscent of a human skull, and is sometimes referred to as the "Skull Nebula."

Rosette Nebula on 12/30

Magnitude: +4.3
Right ascension: 06h32m10s
Declination: 5°03'N
Constellation: Monoceros

Plan your observations

Now that you know which celestial events are occurring in the night sky this month, make sure to plan for your observation sessions. Some of the events discussed above can be seen without any special optical equipment. However, a quality pair of binoculars or a premium telescope will significantly enhance your viewing experience.

If you're in the market for purchasing or upgrading your astronomy gear, we have a curated selection of binoculars, telescopes and accessories from which to choose. Our online store offers high quality optics from industry-leading brands at value prices to help you explore the world above.

Feel free to browse our telescope collection or browse our binoculars.

If you are not sure where to begin, you may read our blog post How To Choose The Right Telescope or How To Choose The Right Binoculars for additional guidance.

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December 2023 Astronomy Events