This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Saturday, March 22, 2025.
Information updated weekly or as needed.
Times given as local St. Louis time this week will be in Daylight Saving Time. 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 -5 hours when CDT. Times posted in the Night Sky Update are in the 24-hour format.
Join us for our next star party, Friday, April 4, 2025, held in association with the St. Louis Astronomical Society.
Observing Highlight of the Week
The image above shows the position of Cassiopeia and Ursa Major relative to the North Star at 20:00 near the start of spring. If you watch these patterns through the year they will appear to chase one another around the North Star in a counterclockwise direction.
For thousands of years, observations of the sky provided us a sense of consistency or predictability. Realizing this, our ancestors understood that the sky represented a kind of cosmic clock that could be used to track changes on Earth. Seasonal changes, wet seasons, stormy seasons, agricultural cycles, navigation and much more can be tracked by watching what is in the sky at a given time.
A tool that was developed to aid these observations was constellations, those imagined patterns of stars we still look for today. As the year progresses, the patterns we see at night slowly change due to Earth’s revolution of the Sun.
While most constellations rise and set each night due to Earth’s rotation, a small part of the sky remains visible all year. These are called circumpolar constellations which appear to circle around the North Star all night. The size of the circumpolar sky varies depending on your latitude which determines how much of the sky is circumpolar. The closer to the North Pole, the larger your circumpolar sky is.
For many observers, the circumpolar constellations Cassiopeia and Ursa Major offer us a simple way to track the seasons. If you go outside tonight once it is dark after sunset, the W-shape of Cassiopeia is in the northwest while the Big Dipper, the asterism most look for when searching for Ursa Major, will be in the northeast. This is where you will always find them at the start of spring after sunset.
Six months later, at the start of fall, you will find Cassiopeia in the northeast and the Big Dipper in the northwest. Keep in mind this is assuming you are observing once it is dark after sunset.
For summer and winter, a similar behavior can be noted except you will find these patterns north or south of one another. At the start of summer, Cassiopeia is found low to the northern horizon after sunset while the Big Dipper will appear high above the northern horizon. At the start of winter, Cassiopeia is nigh in the north while the Big Dipper is low in the north after sunset.
Once a new season starts, Cassiopeia and the Big Dipper slowly start to shift in a counterclockwise direction relative to the North Star. Each night appearing closer to the position it will reach at the start of the next season.
A good way to explore this behavior is to go outside on the first night of a season and sketch the star patterns you see in the north after sunset. I would recommend using Cassiopeia and the Big Dipper, but adding others is always useful. How are they changing? Are there any other patterns you can find that provide similar insights? The need to track the sky is no longer necessary, however, it is still full of insights for those willing to look.
T CrB Nova Update 3/23/2025
If you are still interested in seeing the recurrent nova T Coronae Borealis, there is still hope. The nova has not yet occurred meaning we are in a waiting game. It could happen this year or it could happen next year. We will have to wait and see. If you are still interested in this event, the part of the sky the nova will appear in is rising earlier each night. By midnight, the constellation Corona Borealis will be found high in the eastern sky. Spaceweather.com is still posting magnitude estimates from the AAVSO. This is the resource I recommend following to keep up with any changes in the star’s brightness. Current magnitude of the system is 10.5.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 07:01 on Saturday, March 22 and sunset is at 19:15 providing a little over 12 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 20:45 this week. For those with a sundial, local noon occurs around 13:08 on March 22, 2025.
Moon
Moonrise for Saturday, March 22, was at 02:46 and moonset occurred at 11:37. The Moon starts the week off with a waning crescent phase exhibiting 44% disk illumination. By the end of the week the Moon will exhibit a waxing crescent phase with 4% disk illumination. New moon occurs on March 29, 2025, at 05:58 CDT.
International Space Station (ISS) Observing
Passes of ISS visible from St. Louis for the week of March 22, occur in evening 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 south at 20:00 on March 23, 2025. Credit: Stellarium, EG
This week, two naked eye planets are visible. Mars and Jupiter will be visible shortly after sunset.
Mars
Look for Mars overhead after sunset. It is currently found near the bright stars Castor and Pollux. The current apparition of Mars will continue throughout the rest of 2025. Watch for the Red Planet as it shifts westward through the year. Mars sets around 03:54 this week.
Jupiter
Jupiter will be visible high in the west not long after sunset. Jupiter sets by 1:05, remaining visible a little past midnight. Jupiter reaches superior conjunction on June 24, 2025. We have about three months remaining in the current apparition of Jupiter.
Our next Star Party will be held on Friday, April 4, 2025, from 6:30 pm until 9:30 pm
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 April 4, join us indoors in our planetarium theater for our “Monthly Sky Lecture”.
This free, indoor star program will introduce you to the current night sky. Doors open 15 minutes before show time. Once a show is underway, there are 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: March 22-30, 2025
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