This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Sunday, May 25, 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, June 6, 2025, held in association with the St. Louis Astronomical Society.
Observing Highlight of the Week
In 2009, the Hubble Space Telescope captured the moon Titan transiting Saturn. Additionally, you can see Titan’s shadow cast onto the cloud tops of Saturn. Credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)
Saturn is our highlight this week because on May 31, 2025, we have an opportunity to view an event that is only possible when Saturn is near an equinox. Once Saturn clears tree lines on May 31, you will be able to see a Titan shadow transit if you have a telescope.
Transits are a type of syzygy that occurs when a small body passes in front of a larger one. This can be a planet such as Mercury and Venus transiting the Sun or a moon such as Titan, transiting the planet it orbits. When moons transit the planet they orbit, if the angle is right, they will cast their shadow onto the planet.
Shadow transits are common to see on Jupiter because its rotational access is only tilted about 3.13°. This places the orbits of several Jovian moons within the line of sight between Earth and Jupiter. Saturn on the other hand has an axial tilt of 26.73°. Due to this tilt, transits on Saturn are only visible when Saturn is near an equinox. With an orbital period of 29.5 years, Saturn reaches an equinox every 15 years.
May 31, 2025, is not the only shadow transit we can see this year. Through October 2025, there are 8 other shadow transits that will be visible in the western hemisphere. Sky and Telescope posted these dates in an article you can find here.
Saturn rises at 02:35 on May 31, 2025. By 03:30, Saturn will appear roughly 10° above the western horizon. For some, the planet will be clearing tree lines at this time. By 04:30, Saturn will be about 22° above the horizon. The shadow transit begins at 09:49 UTC or 04:49 CDT. Be aware that nautical twilight begins at 04:29 CDT.
T CrB Nova Update 5/25/2025
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 10.2.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 05:41 on Sunday, May 25 and sunset is at 20:15 providing over 14 hours of daylight. Even after sunset, light from the Sun will dimly illuminate our sky for about 2 hours. This period is called twilight, which ends around 22:07 this week. For those with a sundial, local noon occurs around 12:58 on May 25, 2025.
Moon
Moonrise for Sunday, May 25, was at 04:13 and moonset occurs at 19:00. On May 25, 2025, the Moon will exhibit a waning crescent phase with 2% disk illumination. By June 2, 2025, the Moon will exhibit a waxing crescent phase with 49% disk illumination. New moon occurs on May 26, 2025, at 22:02 CDT.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of May 25 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 south at 20:50 on May 25, 2025. Credit: Stellarium, EG
Looking east at 04:45 on May 26, 2025. Credit: Stellarium, EG
Four naked eye planets will be visible this week. Mars and Jupiter are visible after sunset once it is dark in the west. Venus and Saturn 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 03:41. Look for Venus in the east around 05:00 as it clears tree lines.
Mars
Look for Mars high in the western sky after sunset. Mars has shifted into the constellation Leo. 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 01:04.
Jupiter
Jupiter will be visible low in the west not long after sunset. Views of Jupiter are coming to an end soon. Jupiter reaches superior conjunction on June 24, 2025. As we get closer to this date, Jupiter will be lost to the glare of the Sun. Jupiter sets this week around 21:50.
Saturn
Saturn can be found in the east before sunrise. Around 04:30, Saturn will appear roughly 17° above the eastern horizon and about 17° south of Venus.
Our next Star Party will be held on Friday, June 6, 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 June 6, join us indoors in our planetarium theater for a monthly 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 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: May 25-June 2, 2025
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