This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, December 31, 2024.
Information updated weekly or as needed.
Times given as local St. Louis time this week will be in Central Standard Time (CST). For definitions of terminology used in the night sky update, click the highlighted text. If relying on times posted in Universal Time (UT), St. Louis is -6 hours when CST.
Join us for our next star party, Friday, February 7, 2025, held in association with the St. Louis Astronomical Society. For details, see the information at the bottom of this page or visit https://www.slsc.org/explore/mcdonnell-planetarium/public-telescope-viewings/
Observing Highlight of the Week
On January 19, 2025, Venus and Saturn will reach conjunction. Look for the planets in the southwest after sunset. Image created using Stellarium.
This week the Moon will pass by the planets Venus and Saturn from January 3-4, 2025. The grouping of these three objects will be an excellent target not long after sunset. Each month the Moon will pass by both planets with the next opportunity coming from January 31, 2024, to February 2, 2025. You will also notice that Venus and Saturn will appear to have swapped places. Because Venus is closer to the Sun, it moves faster than Saturn and as result, the motion of Venus will outpace Saturn. The position swap occurs on January 19, 2025, as the pair of planets reach conjunction.
Conjunctions occur when two or more astronomical objects share the same right ascension. For Venus and Saturn, this occurs on January 19, 2025. From St. Louis, the pair of planets will set before the moment of conjunction. Regardless of this, when visible that night, Venus and Saturn will appear about 3° apart.
Venus
Over the last few Months, Venus has been climbing higher in the southwest after sunset. The current evening apparition of Venus will last until March 22, 2025, when Venus reaches inferior conjunction. This occurs when Venus passes between Earth and the Sun. Each year, Venus exhibits an evening and morning apparition. The next morning apparition of Venus begins in April 2025 and ends on January 6, 2026, just before the planet reaches superior conjunction.
If you point a telescope at Venus, you will notice that like the Moon, Venus exhibits phases. Venus can be seen during its gibbous, quarter and crescent phases. The order of the phases depends on whether it is an evening or morning apparition. During an evening apparition, Venus transitions from a gibbous phase after superior conjunction, to a quarter phase when at dichotomy and finally through its crescent phases before inferior conjunction.
Venus reaches maximum eastern elongation on January 10, 2025. This is when we see the greatest angular separation between the Sun and Venus. A day later, Venus reaches dichotomy. Each day after this, Venus will appear nearer the Sun as it heads towards inferior conjunction.
Venus is brightest a little before and after inferior conjunction. Venus’s next greatest illuminated extent occurs on February 14, 2025. If you know how to find Venus in the daytime, you might be able to spot the planet without the assistance of binoculars or a telescope. While this is a possibility, only attempt this if you know where to look. Venus’s solar elongation on this day will roughly 40°. Make sure to position yourself so the Sun is out of view.
Saturn
Unfortunately, we are seeing Saturn approach the end of another apparition. Saturn will remain visible in the west until March 2025. On March 14, 2025, Saturn reaches superior conjunction. Nearing the end of February 2025, Saturn will become increasingly difficult to find as it approaches the glare of the Sun. While we still have it in view, those with telescopes should keep an eye on the rings of Saturn. Saturn reaches an equinox next year on May 6, 2025. Because of this, the apparent tilt of Saturn’s rings has been decreasing all year. Saturn’s rings will eventually appear edge on when viewed from Earth in what is called a ring plane crossing. Sadly, this occurs on March 23, 2025, which is just days after superior conjunction.
While we will not see the ring plane crossing, the months leading up to it and after will still present us with a great opportunity to see Saturn’s rings nearly edge on. Make sure to observe this display while you can otherwise you will have to wait another 15 years to see it the next time. If this interests you, I recommend reading an article from EarthSky on the subject. You can find that at
https://earthsky.org/space/saturns-rings-are-disappearing-march-2025/
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 7:18 a.m. on Tuesday, December 31 and sunset is at 4:50 p.m. providing about 9.5 hours of daylight. Even after sunset, light from the Sun will dimly illuminate our sky for about 1 hour and 30 minutes. This period is called twilight, which ends around 6:25 p.m. this week. For those with a sundial, local noon occurs around 12:05 p.m. on December 31, 2024.
Moon
Moonrise for Tuesday, December 31, was at 8:19 a.m. and moonset occurred at 5:31 p.m. The Moon starts the week off with a waxing crescent phase exhibiting 1% disk illumination. By the end of the week the Moon will exhibit a waxing gibbous phase with 71% disk illumination. First quarter moon occurs on January 6, 2025, at 5:56 p.m.
International Space Station (ISS) Observing
There are several visible passes of ISS from St. Louis for the week of December 31. They occur during morning hours. The table below lists the best of these passes that will be seen from St. Louis. If you do not live in the area, you can use https://heavens-above.com/ to set your viewing location and get times for where you are.
Magnitude (Mag): The Measure of brightness for a celestial object. The lower the value is, the brighter the object will be.
Altitude (Alt): The angle of a celestial object measured upwards from the observer’s horizon.
Azimuth (Az): The direction of a celestial object, measured clockwise from an observer’s location with north being 0°, east being 90°, south being 180° and west being 270°.
Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:
The Visible Planets
Looking southeast at 5:30 p.m. on December 31, 2024. Credit: Stellarium, EG
Looking south at 10:30 p.m. on December 31, 2024. Credit: Stellarium, EG
This week, four naked eye planets are visible. All four are visible in the evening sky with Venus, Jupiter and Saturn visible not long after sunset. Mars rises a little later, becoming visible in the later evening hours.
Venus
Venus will be visible in the southwest after sunset. You can start looking for Venus about 15 minutes after the Sun sets. Venus will set by 8:33 p.m.
Mars
Mars rises at 6:15 p.m. and should be visible in the east after 7:30 p.m. Mars will reach opposition next year on January 15, 2025.
Jupiter
Now past opposition, Jupiter rises before the Sun sets. Look for Jupiter in the east as the sky begins to darken.
Saturn
Saturn will be visible in the southwest shortly after sunset. Saturn now sets around 9:56 p.m. Each week Saturn will set about 25 minutes earlier than it did the week before.
Our next Star Party will be held on Friday, February 7, 2024, from 5:30 p.m. until 8:30 p.m.
On the first Friday of each month, the St. Louis Astronomical Society and the Saint Louis Science Center will set up a number of telescopes outdoors and be on-hand to answer your questions. Telescope viewing begins once it is dark. Regardless of the weather on February 7, join us indoors in our planetarium theater for our “Monthly Sky Lecture.” Showtime is at 7 p.m.
This free, indoor star program will introduce you to the current night sky. Doors open 15 minutes before show time. Shows begins at 7 p.m. Sorry, no late admissions due to safety issues in the darkened theater.
The St. Louis Astronomical Society helps host the monthly Star Parties at the Saint Louis Science Center. In addition to our nighttime viewings, they also help facilitate our daytime event called Solar Sundays. These daytime viewing sessions occur on the 3rd Sunday of each month. Visit SLAS’s website linked above to learn about other telescope events SLAS hosts around the St. Louis area.
James S. McDonnell Planetarium
Night Sky Update: December 31, 2024-January 8, 2025
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