This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Saturday, September 13, 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, October 3, 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
This week Saturn reaches opposition; another Titan shadow transit occurs and fall officially begins for the northern hemisphere. All three astronomical events are great reasons to get out and observe the sky by whatever means you have available.
On September 22, 2025, Earth reaches its September equinox. For us in the northern hemisphere, fall begins while in the southern hemisphere spring begins. As we transition into fall, our daytime hours continue to decrease, increasing the amount of time we have with dark skies. The day in which we have equal hours of day and night is called equilux. This date varies depending on what sunrise/sunset calculations you rely on. The calculations we use in the blog are from the table calculated by NOAA Global Monitoring Laboratory. Based on their calculations, it appears equilux falls between September 25 and 26, 2025.
Along with the increase in nighttime hours, the fall sky is now well placed for observation once it is dark. For those new to observing, bright constellations such as Cassiopeia, Perseus, Pegasus and Andromeda are ideal to start with. Once you can find these constellations you can start tracking down deep sky objects such as the Andromeda Galaxy, the Perseus Double Cluster and asterisms such as Kemble’s Cascade.
Saturn currently resides in the fall sky and will do so for the next few years. Saturn’s wandering behavior will carry it through the constellations Pisces and Aries. By September 2029, Saturn will have shifted into Taurus starting its journey through the winter sky. This wandering behavior of the planets is how our ancestor knew they were different. If you watch them over several months, you will clearly see planets move independently from the background sky. To find Saturn this week, look southeast around 22:00. There you will find a bright square shape of stars called the Great Square of Autumn. Saturn is the brightest object south of the square. If you think you have spotted Saturn you can confirm this if the object does not appear to twinkle.
Saturn reaches opposition this year on September 21, 2025, which is when the planet appears near the anti-solar point in the sky. As Saturn reaches opposition it will appear its brightest for the current apparition making it the ideal time to view Saturn. While telescopes are necessary to see details on Saturn, naked eye observations allow you to track the changing brightness of the planet. Over the next few months, you may be surprised by how much Saturn dims over the rest of this year.
If you have a telescope, Saturn is one of the best objects to view if you live in light polluted areas. With decent viewing conditions and a moderate sized telescope, it is possible to spot details in Saturn’s rings, banding in Saturn’s clouds and several of Saturn’s moons.
This week you can also try to see one of the last Titan shadow transits before we have to wait another 15 years for the next opportunity. These events are only visible if Saturn is near an equinox which occurred earlier this year in May. The 15-year wait is due to how long Saturn takes to orbit the Sun. With an orbital period that is nearly 30 years, the next equinox for Saturn will be in 15 years. The next Titan shadow transit occurs on September 20, 2025, starting at 05:09 UTC and ending at 07:34 UTC. From St. Louis, these times would be 00:09 CDT and 02:34 CDT.
T CrB Nova Update 9/14/2025
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 the west once it is dark. By 22:30, the constellation Corona Borealis will be hard to find due to tree lines or buildings. 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 10.1.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 06:41 on Saturday, September 13 and sunset is at 19:12 providing between 12 and 12.5 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 20:42 this week. For those with a sundial, local noon occurs around 12:57 on September 13, 2025.
Moon
Moonrise for Saturday, September 13, is at 22:53 and moonset occurs at 14:55 the following day. On September 13, 2025, the Moon will exhibit a waning gibbous phase with 56% disk illumination. By September 26, 2025, the Moon will exhibit a waxing crescent phase with 23% disk illumination. Last quarter moon occurs on September 14, 2025, at 05:33 CDT and new moon occurs on September 21, 2025, at 14:54 CDT.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of September 13 occur during evening hours. The table below lists the best of these passes. 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 east at 20:30 on September 14, 2025. Credit: Stellarium, EG
Looking east at 05:30 on September 15, 2025. Credit: Stellarium, EG
Three naked eye planets will be visible this week. Saturn is visible around 20:30. Venus and Jupiter are visible before sunrise in the east.
Venus
Venus is found in the east before sunrise for the rest of the year. It currently rises around 04:25. Look for Venus in the east around 05:30. Venus reaches superior conjunction on January 6, 2026.
Jupiter
This week, Jupiter rises around 01:34. Look for Jupiter in the east around 02:30. Jupiter reaches opposition on January 10, 2026. As we continue towards this date, Jupiter will continue to rise
Saturn
Saturn is now visible in the southeast around 20:30. It will be easy to spot as it is the brightest object in that part of the sky. Saturn rises this week around 19:32. Saturn reaches opposition this month on September 21, 2025.
Our next Star Party will be held on Friday, October 3, 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 October 3, join us indoors in our planetarium theater for our free monthly sky lecture.
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 every third Sunday each month from 11:00-15:00 weather permitting. 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: September 13-26, 2025
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