This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, June 25, 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

The Constellation Sagitta Rising in the East at 10:30 pm
Credit: Stellarium, EG

This week we will highlight another minor constellation of the summer sky. The constellation for this week is Sagitta the Arrow. This is the third smallest constellation, covering only 0.194% of the sky. Its brightest star is Gamma Sagittae, which has an apparent magnitude of 3.47. Sagitta is an ancient constellation that can be found in Ptolemy’s list of 48 constellations. It is often seen as the arrow that Hercules used to kill the eagle Aquilla, who was said to repeatedly eat the liver of Prometheus as a punishment for giving fire to humanity.

Sagitta can be found just north of the constellation Aquila. The easiest way to locate the arrow is to find the bright star Altair in Aquila. Altair is part of the well-known Summer Triangle seen in the eastern sky after sunset this week. The triangle consists of the three bright stars Deneb, Vega and Altair. The southernmost star in the Summer Triangle is Altair. Once you can find Altair, look about 10° north and you will see Sagitta. It has four moderately bright stars that form an asterism shaped like an arrow.

Sagitta is home to an interesting star cluster named Messier 71 (M71). Over the years, the nature of M71 has been debated. Originally, M71 was classified as a dense open star cluster due to the lack of dense central concentration. Additionally, its stellar members have higher amounts of metals than would be expected in globular star clusters. Eventually, stars belonging to the horizontal branch of the H-R Diagram were discovered in M71, which are stars often found in globular clusters. Additionally, the estimated age of 9-10 billion years would be much older than open star clusters. Today you will find M71 listed as a globular cluster, which are ancient denizens of the Milky Way Galaxy. M71 is a “young” globular cluster with an estimated age of 9-10 billion years old. To find M71, you will need to identify the stars Gamma and Delta Sagittae. A star chart is the easiest way to identify these stars. Once you find them, M71 will be found halfway between them. M71 has an apparent magnitude of 6.1 so it should be easy to find with most binoculars. It will appear as a faint cotton-ball-shaped patch of light.

The Sun and Moon

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

Sunrise is at 5:38 a.m. on Friday, June 25 and sunset is at 8:30 p.m. providing us with nearly 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 10:28 p.m. this week. For those with a sundial, local noon occurs around 1:04 p.m. this week.

2021-06-25 5:38 a.m.8:30 p.m.
2021-06-265:38 a.m.8:30 p.m.
2021-06-27 5:39 a.m.8:30 p.m.
2021-06-28 5:39 a.m.8:30 p.m.
2021-06-29 5:40 a.m.8:30 p.m.
2021-06-30 5:40 a.m.8:30 p.m.
2021-07-01 5:40 a.m.8:30 p.m.
2021-07-02 5:41 a.m.8:29 p.m.
2021-07-03 5:41 a.m.8:29 p.m.


Moonrise for Friday, June 25 occurs at 9:55 p.m. and moonset will occur at 7:24 a.m. on the following morning. On Friday, June 25 the Moon will exhibit a waning gibbous phase with 98% of the lunar disk illuminated. Last quarter moon occurs on July 1 at 4:11 p.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of June 25 occur during morning hours. The best passes this week occur on the mornings of June 28 and July 1. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, June 25

Date Starts  Max. altitude  Ends  
26 Jun-2.1 04:11:1917S 04:12:5924SE 04:15:4710ENE
27 Jun-1.4 03:25:4714SE 03:25:4714SE 03:27:3310E
27 Jun-3.4 04:58:5210WSW 05:02:1157NW 05:05:3010NE
28 Jun-3.8 04:13:0128SW 04:14:3781SE 04:18:0010NE
29 Jun-3.1 03:27:0843SE 03:27:0843SE 03:30:1410ENE
29 Jun-1.9 05:01:0810W 05:03:5624NNW 05:06:4410NNE
30 Jun-1.3 02:41:0716E 02:41:0716E 02:42:0910ENE
30 Jun-2.6 04:14:0218W 04:16:0235NNW 04:19:1010NE
01 Jul-3.5 03:27:5156WNW 03:28:0658NW 03:31:2610NE
01 Jul-1.1 05:03:3810NW 05:05:2714NNW 05:07:1610NNE
02 Jul-2.1 02:41:3132ENE 02:41:3132ENE 02:43:2910NE
02 Jul-1.3 04:14:5110WNW 04:17:1318NNW 04:19:3610NNE
03 Jul-1.9 03:27:5621WNW 03:28:5724NNW 03:31:4710NNE

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 pm, June 25, 2021
Credit: Stellarium, EG, 

Looking Southeast, at 2:00 am, June 26, 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 10° 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 10:34 p.m. If you watch Mars and Venus as we head 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. 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 11:38 p.m. and will be easy to see in the southeast by 12:30 a.m.


Saturn has returned to our evening sky. Saturn rises at 11:11 p.m. and will be easy to spot by 12:00 a.m. looking southeast.

James S. McDonnell Planetarium

Night Sky Update: June 25-July 3, 2021