This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Saturday, October 11, 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, November 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 Comets C/2025 A6 (Lemmon) & C/2025 R2 (Swan)
This image shows location of comet C/2025 A6 (Lemmon) from October 10-16, 2025, at 5 am from St. Louis, Missouri. As the week progresses, the comet will continue to be found lower to the horizon making it more difficult to find. Image created using Stellarium.
C/2025 A6 (Lemmon) Update
C/2025 A6 (Lemmon) continues to brighten as it heads towards its perihelion on November 8, 2025. Recent observations put the comet between 5.3 and 6.0 magnitudes making it an easy target from light polluted areas if you are able to identify the star field that comet appears in. C/2025 A6 (Lemmon) is still passing through Ursa Major and will continue to do so through the 13th. It will shift into the constellation Canes Venatici By October 14, 2025, which is when the comet becomes more accessible in the early evening.
Using 10×50 binoculars, I last observed C/2025 A6 (Lemmon) on October 9, 2025, and was surprised how much easier it was to see. Its dim coma stood out in the star field much more than it had just a few days prior. Previously I required a telescope to notice the bright core of the coma however it was easy to see in binoculars when I last looked. I also felt for the first time the coma looked a bit elongated. Hopefully this is hinting that soon the comet’s tail will be visible in binoculars.
C/2025 A6 (Lemmon) was discovered by the Mount Lemmon Survey in images captured on January 3, 2025. Astronomers calculated its inbound orbital period was roughly 1350 years. After the comet passed by Jupiter, its outbound orbit now appears to be around 1155 years.
Current models are showing the comet will likely peak between 3.5 and 4.5 magnitudes when it is nearest to Earth on October 21, 2025, which is dimmer than what they showed last week. This is still bright enough that it could become naked eye visible from light polluted locations. After the comet reaches perigee it will likely remain bright through the end of October.
How bright an object appears to us on Earth is a measure of its intrinsic luminosity, its distance and any extinction of its light caused by dust or atmosphere. The value measured is an object’s apparent magnitude. While 3.5 magnitude is well within naked eye visibility, a given brightness value for a bright star-like object will appear brighter than an extended object like C/2025 A6 (Lemmon) with the same magnitude. The reason for this is the brightness measurement of an object is based on the amount of light emitted across the entire object. Extended objects find their light spread across a larger area resulting in a diffuse appearance.
Recent logs of the comet’s magnitude put it at magnitude 5.5 which means it is bright enough to see naked eye from a dark location. Tracking the comet over the few weeks from a bright suburban sky location with a Bortle 6-7 rating, the comet is easy to find with binoculars provided you can identify specific star fields. The largest binocular I used to spot the comet was 10×50 and the smallest was 8×28.
Once clear skies return to St. Louis, I will continue tacking C/2025 A6 (Lemmon) posting updates when they are relevant. For now, C/ 2025 A6 (Lemmon) remains an early morning target but it might be visible for some after sunset. It is still low to the horizon around 19:15, but those with clear views to the northeast may already be able to find the comet in the evening. If you live outside of St. Louis, your views will vary depending on your latitude. The higher your latitude the better your chances of seeing C/2025 A6 (Lemmon).
When C/2025 A6 (Lemmon) is closest to Earth it will be passing through the constellation Boötes. Looking west around 19:00 on October 21, 2025, you will find the comet a little over 20° above the western horizon at azimuth 288°. To spot the comet on October 21, start by finding the Big Dipper in Ursa Major. This asterism will be found in the northwest at 19:00. Locate the handle of the Big Dipper and follow the direction it points to the west. This will direct you to the bright star Arcturus in the constellation Boötes. Looking east from Arcturus the next bright stars you see are Epsilon, Sigma and Rho Boötis. C/2025 A6 (Lemmon) will be found just below these stars.
This image shows the location of comet C/2025 A6 (Lemmon) on October 21, 2026 at 7 pm when it is closest to Earth. The comet will be found a little over 20° above the western horizon at this time and date. Image created using Stellarium.
C/2025 R2 (SWAN)
You may have also heard there is another comet visible shortly after sunset. This comet is called C/2025 R2 (SWAN). This comet reached perihelion on September 12, 2025, and is now headed away from the Sun. Its peak magnitude reached 5.9 after an outburst in September and has stayed around 6th magnitude since.
I attempted to view this comet in the city using 10×50 binoculars but was unsuccessful. Viewing conditions were decent for St. Louis so I expect darker skies are necessary if only using binoculars.
C/2025 R2 (SWAN) Is currently found in the constellation Scorpius. Over the next week, the comet will pass through the constellations Ophiuchus, Serpens, and Scutum climbing higher in the sky. C/2025 R2 (SWAN) will be closest to Earth on October 20, 2025, so it might become easier to find as long as it remains its current magnitude.
I will continue to track both comets and update these posts when relevant. There are several resources available online if you wish to learn more about these comets and recent observations of them. You can find links to these resources below.
COBS – Comet Observation Database
This image shows the location of comet C/2025 R2 (SWAN) from October 10 to October 22. Image created using Stellarium.
T CrB Nova Update 10/11/2025
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 found low in the west once it is dark. By 21:45, 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 07:06 on Saturday, October 11 and sunset is at 18:28 providing roughly 11.5 hours of daylight at the start of the week and only 11 hours its end. 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 19:56 this week. For those with a sundial, local noon occurs around 12:47 on October 11, 2025.
Moon
Moonrise for Saturday, October 11, is at 17:50 and moonset occurs at 06:20 the following day. On October 11, 2025, the Moon will exhibit a waning gibbous phase with 69% disk illumination. By October 19, 2025, the Moon will exhibit a waning crescent phase with 2% disk illumination. Last quarter moon occurs on October 13, 2025, at 13:13.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of October 11 occur during morning 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 south at 19:15 on October 11, 2025. Credit: Stellarium, EG
Looking southeast at 01:00 on October 12, 2025. Credit: Stellarium, EG
Three naked eye planets will be visible this week. Saturn is visible after sunrise in the east. Jupiter can be found in the east around 2 AM and Venus will be found low in the east around 6 AM
Venus
Venus is found in the east before sunrise for the rest of the year. It currently rises around 05:23. Venus should be high enough for most to see after 06:00. Venus reaches superior conjunction on January 6, 2026.
Jupiter
This week, Jupiter rises around 00:04. Look for Jupiter in the east around 02:00. Jupiter reaches opposition on January 10, 2026. As we continue towards this date, Jupiter will continue to rise earlier each week.
Saturn
Saturn is now visible after sunset in the east once it is dark. Saturn rises this week around 17:41. Now past opposition, Saturn is visible after the Sun sets. Saturn reaches solar conjunction on March 12 next year.
Our next Star Party will be held on Friday, November 7, 2025, from 5:30 pm until 8:30 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 November 7, 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: October 11-19, 2025
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