This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Sunday, October 19, 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 use the button below.
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Observing Highlight Comets C/2025 A6 (Lemmon) & C/2025 R2 (Swan) Near Perigee
This image shows location of comet C/2025 A6 (Lemmon) from October 19-27, 2025, at 7:30 pm from St. Louis, Missouri. Image created using Stellarium.
C/2025 A6 (Lemmon) Updated October 19, 2025
C/2025 A6 (Lemmon) remains the brighter of the two comets with recent magnitude estimates between 4.2 and 4.8. With the comet’s perigee on the 21st, this is likely to be as bright as it gets. It is possible the comet’s magnitude will continue to increase over the next few days, but we are likely near its peak magnitude.
C/2025 A6 (Lemmon) is now visible in evening hours. As of October 19, C/2025 A6 (Lemmon) is still in Canes Venatici, however it shifts into Boötes on October 20, 2025. Your best chance to find this comet starts around 19:30 when twilight is nearing its end.
Current models are showing the comet will likely peak as a 4th magnitude object when it is nearest to Earth. After the comet reaches perigee it will likely remain bright enough to see with binoculars through the end of October and into November.
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 4th 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.
To spot the comet on October 21, start by finding the Big Dipper in Ursa Major. This asterism will be found in the northwest after 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. If you are viewing in light pollution, try to find a spot where you can use buildings or trees to block some of the lights closest to you.
As we go through the week, C/2025 A6 (Lemmon) will increase in altitude placing it in darker parts of the sky. While October 21st is when the comet is nearest to Earth, you may have better luck finding the comet a few days later when it is higher in the sky.
Using 10×50 binoculars, I last observed C/2025 A6 (Lemmon) on October 16, 2025. Even though its magnitude was brighter (4.8) then the last time I saw the comet, it was more difficult to see. This was due to its low altitude placing it in a brighter part of the sky. Additionally, humidity was high which impacted viewing conditions.
For the next few weeks, C/2025 A6 (Lemmon) should remain an easy binocular target if you are viewing from a light polluted area. After October 21st, the comet’s magnitude should begin to decline. If you are interested in tracking this comet, I recommend using the software called Stellarium. This free planetarium software is available for all formats. Once you install the software you will have to update its comet database. Once updated, you can use the software’s search function to find C/2025 A6 (Lemmon)
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) Updated October 19, 2025
C/2025 R2 (SWAN) is beginning to fade as recent estimates are showing the comet has faded to 6.1. This should still be within reach of larger handheld binoculars, but you might need to use a telescope to find it.
C/2025 R2 (SWAN) will be in the constellation Sagittarius when it is nearest to Earth on October 20, 2025. After this date, it shifts through the constellations Aquila, Capricornus and Aquarius. By October 27, 2025, the Moon will interfere with chances of seeing this comet.
The last time I tried to find C/2025 R2 (SWAN), I was unsuccessful. This was on the same night I last viewed C/2025 A6 (Lemon) so viewing conditions were not ideal.
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.
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 19 to October 27. Image created using Stellarium.
T CrB Nova Update 10/19/2025
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 21:30, 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 9.9.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 07:14 on Sunday, October 19 and sunset is at 18:16 providing roughly 11 hours of daylight at the start of the week and only about 10 hours and 40 minutes at 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 19:45 this week. For those with a sundial, local noon occurs around 12:46 on October 19, 2025.
| Day | Sunrise (CDT) | Sunset (CDT) | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 19-Oct | 7:14 | 18:16 | ||||||||||
| 20-Oct | 7:15 | 18:15 | ||||||||||
| 21-Oct | 7:16 | 18:14 | ||||||||||
| 22-Oct | 7:17 | 18:12 | ||||||||||
| 23-Oct | 7:18 | 18:11 | ||||||||||
| 24-Oct | 7:19 | 18:10 | ||||||||||
| 25-Oct | 7:20 | 18:08 | ||||||||||
| 26-Oct | 7:21 | 18:07 | ||||||||||
| 27-Oct | 7:22 | 18:06 |
Moon
Moonrise for Sunday, October 19, was at 05:27 and moonset occurred at 17:20. On October 19, 2025, the Moon will exhibit a waning crescent phase with 2% disk illumination. By October 27, 2025, the Moon will exhibit a waxing crescent phase with 34% disk illumination. New moon occurs on October 21, 2025, at 07:25.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of October 19 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.
| Date | Starts | Max. altitude | Ends | |||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Time | Alt. | Az. | Time | Alt. | Az. | Time | Alt. | Az. | ||
| 20 Oct | -1.8 | 6:18:41 | 15 | NW | 6:19:58 | 17 | NNW | 6:22:20 | 10 | NNE |
| 21 Oct | -1.8 | 5:33:07 | 20 | N | 5:33:07 | 20 | N | 5:34:52 | 10 | NNE |
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 19:30 on October 19, 2025. Credit: Stellarium, EG
Looking southeast at 01:00 on October 20, 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 1 AM and Venus will be found low in the east around 6:30 AM
Venus
Venus is found in the east before sunrise for the rest of the year. It currently rises around 05:39. Venus should be high enough for most to see after 06:30. Venus reaches superior conjunction on January 6, 2026.
Jupiter
This week, Jupiter rises around 23:36. Look for Jupiter in the east after 00:30. 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 17:08 so it should be free of most trees and buildings once it is dark enough to see the planet. 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 19-27, 2025
