This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, July 16, 2021.

Information updated weekly or as needed.

Times given as local St. Louis time, which is Central Daylight Time (CDT). 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.

Public Telescope Viewings

With the changing recommendations from the CDC regarding COVID-19, conversations regarding the return of star parties at the Saint Louis Science Center have begun. We are close to bringing back our public telescope viewings, but a few details still need to be worked out. We will post future updates as we learn more about when we can bring back telescope viewings.

Observing Highlight of the Week


Waxing Gibbous Moon Seen on July 20, 2021 and How to Find Apollo 11 Landing Site
Credit: NASA, SVS, Ernie Wright, LRO

This week we celebrate the 52nd anniversary of the Apollo 11 mission. In 1969, astronauts Neil A. Armstrong, Michael Collins and Edwin “Buzz” E. Aldrin Jr. traveled to the Moon and successfully landed a human payload on its surface for the first time in history. This great achievement was made possible by the Mercury, Gemini and previous Apollo missions that developed the necessary technologies and techniques needed to successfully send and land humans on the Moon. The Moon landing occurred only 12 years after Sputnik and 66 years after the first successful flight of the Wright brothers.

Apollo 11 left Earth on July 16 at 8:32 a.m. CDT. About 50 minutes later, a maneuver called Trans-Lunar-Injection occurred, sending the crew aboard Apollo 11 toward the Moon. On July 19, 1969, Apollo 11 passed behind the Moon on its way to establishing lunar orbit, eventually completing 30 lunar orbits. On July 20, 1969, Armstrong and Aldrin boarded Eagle, separating from Columbia at 11:44 a.m. CDT. Eagle successfully landed on July 20, 1969, at 2:17 p.m. CDT marking the first time humans set foot on the surface of another celestial body.

After spending 21 hours and 36 minutes on the lunar surface, Armstrong and Aldrin ascended from the lunar surface, eventually returning to Columbia in lunar orbit. After roughly 8 days and 3 hours in space, the Apollo 11 crew safely returned to Earth, splashing down in the Pacific Ocean on July 24, 1969. The last Apollo mission to the Moon occurred in December 1972. Apollo 17 was the most recent time humans walked on the surface of the Moon. NASA’s next lunar program, Artemis, is currently under development. Artemis aims to return humans to the lunar surface, which will help pave the way for human exploration of Mars.

Is it possible to see where the Apollo missions landed? The answer is both yes and no. From our backyards, we cannot see the items left behind on the Moon. Things like the lunar modules and the lunar roving vehicles from the later missions are too small to resolve with our backyard telescopes. This said, the Apollo landing sites have been imaged by the Lunar Reconnaissance Orbiter (LRO). LRO was able to resolve some of these details including lunar modules and astronaut footpaths. You can find out more about these images here.

What we can see are where the missions landed. Looking toward the landing sites allows us to see various lunar features that can identify the landing site. This week, the Moon will exhibit phases that are favorable for spotting the landing site of Apollo 11. The key to finding where Apollo 11 landed is to first locate the large, dark feature named Mare Tranquillitatis. Centered at 0.68° N 23.43° E on the lunar surface, Mare Tranquillitatis is one of the large impact basins that later filled with lava that erupted to the lunar surface. The basalts found in Mare Tranquillitatis are dated to about 3.7 billion years old.

Once you have found Mare Tranquillitatis, you want to look for three impact craters in the lower left section near the edge of the mare. The three craters are named Ritter, Sabine and Moltke. Start with Ritter and Sabine as they are easily seen in binoculars. These two large impact craters appear close together, visible on the western edge of the mare. Next, follow the edge of the mare to the south until you find a small crater named Moltke. It has a distinctly brighter albedo than the surrounding area. If you have found Moltke, the Apollo 11 landing site is about 5 crater diameters north and 2.5 crater diameters west.

As we celebrate the 52nd anniversary of Apollo 11, try and spot the other Apollo landing sites! There are several guides to finding them available online. In some cases, binoculars can get you close, but telescopes are recommended.

The Sun and Moon

The Moon as seen from the International Space Station, on July 31, 2011.
Credit: NASA

Sunrise is at 5:50 a.m. on Friday, July 16 and sunset is at 8:24 p.m., providing us with a little less than 15 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for a little less than 2 hours. This period is called twilight, which ends around 10:16 p.m. this week. For those with a sundial, local noon occurs around 1:07 p.m. this week.

2021-07-16 5:50 a.m.8:24 p.m.
2021-07-175:51 a.m.8:24 p.m.
2021-07-18 5:51 a.m.8:23 p.m.
2021-07-19 5:52 a.m.8:22 p.m.
2021-07-20 5:53 a.m.8:22 p.m.
2021-07-21 5:54 a.m.8:21 p.m.
2021-07-22 5:55 a.m.8:20 p.m.
2021-07-235:55 a.m.8:19 p.m.
2021-07-24 5:56 a.m.8:19 p.m.


Moonrise for Friday, July 16 occurs at 12:33 p.m. and moonset will occur at 12:31 a.m. on the following day. On Friday, July 16 the Moon will exhibit a waxing crescent phase with 46% disk illumination. First quarter moon occurs on July 17 at 5:11 a.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of July 16 occur during morning and evening hours. The best pass this week occurs on the evening of July 18. Use the table below for information about this and other visible passes this week.

Catch ISS from St. Louis starting Friday, July 16

Date Starts  Max. altitude  Ends  
17 Jul-0.6 22:09:5110WNW 22:12:0416NNW 22:14:1810NNE
18 Jul-0.5 01:25:5910NNW 01:27:2715N 01:27:2715N
18 Jul-1 21:21:5510W 21:24:3622NNW 21:27:1910NNE
21 Jul-0.8 23:53:4010NNW 23:55:2015N 23:55:2015N
23 Jul-0.8 23:55:2110NNW 23:56:2617NNW 23:56:2617NNW
24 Jul-1.4 23:08:1710NNW 23:10:3520NNE 23:10:3520NNE

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°.

For information about ISS flyovers and other visible satellites, visit

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 9:00 p.m. July 16, 2021
Credit: Stellarium, EG 

Looking Southeast, at 12:00 am, July 17, 2021
Credit: Stellarium, EG 

This week, four naked eye planets are visible. Venus and Mars can be found in the west after sunset. Jupiter and Saturn can be found in the southeast after midnight.


Venus is well into another evening apparition. By 8:50 p.m., Venus will be 12.7° above the western horizon. As 2021 continues, we will see Venus climb higher in the western sky after sunset until October 29 when it reaches maximum eastern elongation. After this date Venus will start to head back towards the Sun as it approaches inferior conjunction on January 8, 2022.


Currently Mars appears as a 1.8-magnitude object that will be visible high in the west about 40 minutes after sunset. Mars sets by 9:49 p.m. The viewing window for Mars is getting shorter. Mars is headed towards superior conjunction on October 7, 2021. As we get closer to this date, Mars will set earlier each night until we lose the Red Planet to the glare of the Sun.


Jupiter is now rising before midnight. Jupiter rises at 10:13 p.m. and will be easy to see in the southeast by 11:00 p.m.


Saturn has returned to our evening sky. Saturn rises at 9:16 p.m. and will be easy to spot by 10:00 p.m. looking southeast.

James S. McDonnell Planetarium

Night Sky Update: July 16-July 24, 2021