This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, July 9, 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

Moon, Mars and Venus on July 12, 2021, 30 Minutes After Sunset
Credit: Stellarium, EG

On July 13, the planets Venus and Mars will exhibit a conjunction. If you have been watching Venus and Mars over the last month, you probably noticed the two planets have been getting closer together. Venus and Mars will reach conjunction at 2:08 a.m. CDT, meaning it will happen when they are below the horizon.

Conjunctions are when two or more celestial bodies temporarily share the same right ascension. A simple way to think of this is the objects will appear close to one another. The closest approach of the objects does not always occur at the time of conjunction. When two celestial bodies appear at their nearest to one another it is an event called an appulse.

The next appulse of Venus and Mars also occurs on July 13, but it is roughly 6 hours after conjunction. The appulse occurs at 8:34 a.m. CDT. For most viewers, this means we will not see the appulse in St. Louis since it occurs in daylight. This said, the pair of planets will be about 7° above the horizon during the appulse. For most observers, we would not recommend trying to find Venus and Mars in the daytime, because the planets will still be near the Sun in the sky.

Due to the daytime occurrence of the conjunction/appulse, our best view in St. Louis will occur on July 12. To see Venus and Mars, look west 30-40 minutes after sunset. Along with the planets, which will be about 0.5° apart, you will find a waxing crescent moon visible about 4° from the planets.

The Sun and Moon

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

Sunrise is at 5:45 a.m. on Friday, July 9, and sunset is at 8:28 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 about 2 hours. This period is called twilight, which ends around 10:22 p.m. this week. For those with a sundial, local noon occurs around 1:06 p.m. this week.

2021-07-09 5:45 a.m.8:28 p.m.
2021-07-10 5:46 a.m.8:27 p.m.
2021-07-11 5:46 a.m.8:27 p.m.
2021-07-12 5:47 a.m.8:26 p.m.
2021-07-13 5:48 a.m.8:26 p.m.
2021-07-14 5:48 a.m.8:25 p.m.
2021-07-15 5:49 a.m.8:25 p.m.
2021-07-16 5:50 a.m.8:24 p.m.
2021-07-17 5:51 a.m.8:24 p.m.


Moonrise for Friday, July 9 occurs at 5:07 a.m. and moonset will occur at 8:37 p.m. On Friday, July 9 the Moon will exhibit a new moon phase. First quarter moon occurs on July 17 at 5:11 a.m. This new moon starts lunation 1219. This number indicates that this lunar cycle is the 1219th cycle since the modern Brown Lunation Number system was initiated.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of July 9 occur during morning and evening hours. The best passes this week occur on the evening of July 13 and the morning of July 14. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, July 9

Date Starts  Max. altitude  Ends  
11 Jul-1.3 23:43:2320NNE 23:43:2320NNE 23:44:4410NE
12 Jul-1.4 04:32:1310NNW 04:35:0927NNE 04:38:0410E
12 Jul-2.1 21:15:4010S 21:17:4816SE 21:19:5610E
12 Jul-2.9 22:51:0210WSW 22:54:2051NW 22:57:3810NE
13 Jul-0.8 03:45:1210NNW 03:47:4419NNE 03:50:1610ENE
13 Jul-3.8 22:03:4110SW 22:07:0388NW 22:10:2610NE
13 Jul-0.7 23:42:0210WNW 23:44:1716NNW 23:46:3310NNE
14 Jul-0.5 02:58:1410NNW 03:00:1615NNE 03:02:1910ENE
14 Jul-3.5 04:34:1310NW 04:37:3571NE 04:40:5710ESE
14 Jul-3.6 21:16:3410SSW 21:19:5050SE 21:23:0810ENE
14 Jul-1.1 22:54:0810W 22:56:5022NNW 22:59:3410NNE
15 Jul-2.4 03:47:0410NW 03:50:1742NNE 03:53:3110ESE
15 Jul-1.8 22:06:2310W 22:09:2731NNW 22:12:3110NE
16 Jul-1.6 02:59:5810NNW 03:02:5627NNE 03:05:5310E
16 Jul-3.1 04:36:4110WNW 04:39:4634SW 04:42:5110SSE
16 Jul-2.7 21:18:4910WSW 21:22:0649NW 21:25:2410NE
17 Jul-1 02:12:5710NNW 02:15:3020NNE 02:15:4420NNE
17 Jul-0.6 22:09:4910WNW 22:12:0316NNW 22:14:1710NNE

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 10, 2021
Credit: Stellarium, EG 

Looking Southeast, at 1:00 am, July 11, 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 9:00 p.m., Venus will be 11.3° above the west-northwest 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 10:05 p.m. If you watch Mars and Venus as we continue into July this year, you will see the two planets are getting closer in the sky. Mars and Venus are headed towards a conjunction on July 13, 2021. The conjunction happens before we seem them that day, so it is best to look for the pair on July 12 about 30 minutes after sunset. You will see the two planets less than 1° apart.


Jupiter is now rising before midnight. Jupiter rises at 10:42 p.m. and will be easy to see in the southeast by 11:42 p.m.


Saturn has returned to our evening sky. Saturn rises at 9:45 p.m. and will be easy to spot by 10:45 p.m. looking southeast.

James S. McDonnell Planetarium

Night Sky Update: July 9-July 17, 2021