This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Sunday, June 29, 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, August 1, 2025, held in association with the St. Louis Astronomical Society.
Observing Highlight of the Week
This week we have a brief window to observe the planet Mercury. The nearest planet to the Sun has started a brief evening apparition. You can find the planet in the west about 30 minutes after sunset. For about a week, those with clear views of the western horizon can spot Mercury before it is lost to the Sun’s glare.
For those new to observing planets, Mercury and Venus never stray far from where the Sun appears in the sky. This happens because they are both closer to the Sun than Earth. As a result, both planets are only visible in the east before sunrise or in the west after sunset. If you have ever heard Venus referenced as the morning or evening, it is due to this behavior.
Mercury reaches its maximum elongation from the Sun on July 4, 2025, which is 26° for this apparition. Over the next few days if the sky clears up after sunset, look west and you might spot Mercury.
Titan Shadow Transit 7/2/2025 and 7/18/2025
Titan’s next shadow transit occurs on July 2, 2025, followed by a transit on July 18, 2025. The transit on July 2 begins at 02:40 CDT and ends at 08:03 CDT. From St. Louis we will only see about 1/2 of the transit before sunrise. Around the start of the transit, you will find Saturn about 24° above the eastern horizon at 113° azimuth.
The transit occurring on July 18, 2025, begins at 02:00 CDT and ends at 07:00 CDT. From St. Louis, we will see about 2/3 of the transit before the Sun rises. When the transit begins, Saturn will be roughly 28° above the eastern horizon around 118° azimuth.
You will need a telescope to see Titan’s shadow transit across the clouds of Saturn. While the transit is underway, you will also see Titan to the east of Saturn. Saturn’s rings will still appear thin however we are starting to see the underside of the ring system. If you would like to plan for future transits of Titan’s shadow make sure to read Bob King’s article on Sky and Telescope which can be found here.
T CrB Nova Update 6/29/2025
f 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 is overhead once it is dark. By 03:00, the constellation Corona Borealis will be found low in the western 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 10.1.
The Sun and Moon
The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA
Sun
Sunrise is at 05:39 on Sunday, June 29 and sunset is at 20:29 providing close to 15 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 22:27 this week. For those with a sundial, local noon occurs around 13:05 on June 29, 2025.
Moon
Moonrise for Sunday, June 29, was at 10:07 and moonset occurs at 23:40. On June 29, 2025, the Moon will exhibit a waxing crescent phase with 23% disk illumination. By July 7, 2025, the Moon will exhibit a waxing gibbous phase with 92% disk illumination. First quarter moon occurs on July 2, 2025, at 14:30 CDT.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of June 29 occur during morning and evening hours. The table above 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 west at 21:15 on June 29, 2025. Credit: Stellarium, EG
Looking east at 04:15 on June 30, 2025. Credit: Stellarium, EG
Four naked eye planets will be visible this week. Mercury is briefly visible in the west after sunset. Mars is visible in the west after sunset once it is dark. Venus and Saturn are visible before sunrise in the east.
Mercury
Mercury is briefly visible in the west after sunset this week. The next few days are your best opportunity. Look west about 20 to 30 minutes after sunset.
Venus
Venus is found in the east before sunrise for the rest of the year. It currently rises around 03:00. Look for Venus in the east around 04:00 as it clears tree lines.
Mars
Look for Mars in the western sky after sunset. 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 23:35.
Saturn
Saturn can be found in the east before sunrise. Saturn rises around 00:44 this week. The planet should be high enough to see by 02:00. If you missed the last Titan shadow transit, the next two occur on July 2 and 18, 2025.
Our next Star Party will be held on Friday, August 1, 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 August 1, 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 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: June 29-July 7, 2025
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