This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, September 4, 2020.

Information updated weekly or as needed.

Times given as local St. Louis time (CDT).  For definitions of terminology used in the night sky update, click the highlighted text.

Public Telescope Viewings

Star parties at the Saint Louis Science Center have temporarily been canceled due to recommendations from the CDC regarding COVID-19. All public telescope events are canceled until further notice. As conditions change, we will reevaluate and update this article once public observing events resume.

Observing Highlight of the Week

Simulated view of Moon and Mars Conjunction September 5, 2020
Credit: Stellarium, EG

This week the Moon and Mars will reach conjunction. This occurs on September 5 at 11:46 p.m. Conjunctions are when two or more astronomical bodies share the same right ascension. This paring of the Moon and Mars is listed at only one arc minute apart during conjunction. Learn more about this conjunction here.

Conjunctions are nice events that provide a great view for any means of observation. As the Moon and Mars rise on September 5 they will make for a beautiful pair as they transit the sky. Those with telescopes should be able to see the pair together in one field of view. When observing Mars, you will find dark and light patches called albedo features. The easiest feature on Mars to see are its polar ice caps.  For the current Martian apparition, it is the southern ice cap that is visible from Earth.

Views of the Martian surface will continue to improve as we head towards opposition on October 13. Opposition with Mars occurs every 26 months which is when Mars will be at it brightest and near its closest to Earth for its current orbit.

The Sun and Moon

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

Sunrise is at 6:33 a.m. on Friday, September 4 and sunset is at 7:26 p.m. providing us with just under 13 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for about 1 hour and 30 minutes. This period is called twilight, which ends around 8:58 p.m. this week. For those with a sundial, local noon occurs around 1:00 p.m. this week.

2020-09-04 6:33 a.m.7:26 p.m.
2020-09-05 6:34 a.m.7:24 p.m.
2020-09-06 6:35 a.m.7:23 p.m.
2020-09-07 6:36 a.m.7:21 p.m.
2020-09-08 6:37 a.m.7:19 p.m.
2020-09-09 6:38 a.m.7:18 p.m.
2020-09-10 6:39 a.m.7:16 p.m.
2020-09-11 6:40 a.m.7:15 p.m.
2020-09-12 6:41 a.m.7:13 p.m.


Moonrise for Friday, September 4 occurs at 9:00 p.m. and moonset will occur at 9:38 a.m. on the following day. On Friday, September 4 the Moon will exhibit a waning gibbous phase with about 94% of the lunar disk illuminated. Last quarter moon occurs on September 10 at 4:26 a.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of September 4 occur during morning hours. The best passes this week occur on September 10 and 12. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, September 4

DateStartsMax. altitudeEnds
08 Sep-1.2 05:34:1510NNW 05:36:4920NNE 05:39:2410ENE
09 Sep-0.9 04:46:5210NNW 04:48:5715NNE 04:51:0010ENE
10 Sep-2.6 05:35:1510NW 05:38:2943NNE 05:41:4210ESE
11 Sep-1.8 04:49:0219NNW 04:50:4128NNE 04:53:3810E
12 Sep-0.7 04:04:0516NE 04:04:0516NE 04:05:2310ENE
12 Sep-3.8 05:37:0614WNW 05:39:5261SW 05:43:1010SE

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 Southeast, at 10:30 pm, September 4, 2020
Credit: Stellarium, EG

Looking East, 4:00 am, September 5, 2020
Credit: Stellarium, EG

This week, four naked eye planets are visible. Jupiter and Saturn rise before sunset. Look for them in the south once it is dark. Mars rises in the late evening and will be best seen after midnight. Venus can be found in the eastern sky before sunrise.

For those tracking Jupiter and Saturn as they approach their great conjunction later this year, the two gas giants currently appear about 8.3° apart in the sky. Jupiter appears to be moving away from Saturn right now due to retrograde motion. This is all an illusion caused by Earth passing by slower moving Jupiter. Saturn is also exhibiting retrograde motion. If you keep watching these planets as 2020 progresses, you will see some interesting behaviors that inspired early astronomers to track the skies.


Venus is well into another morning apparition. After months of seeing Venus in the west after sunset Venus is now visible in the east before sunrise. Venus rises at 2:53 a.m. and will be easily seen by 3:45 a.m. Venus remains a morning object until March 26, 2021 when it reaches superior conjunction. Since Venus has passed greatest western elongation, it will start to exhibit a gibbous phase.


The red planet rises around 9:30 p.m. and will be high enough to see in the southeast by 10:30 p.m. Opposition for Mars occurs on October 13, 2020. As we head towards this date Mars will appear brighter and larger through a telescope improving surface details. Surface features are already visible when viewing conditions are favorable. Current apparent brightness of Mars is -1.9 magnitude. At this magnitude Mars will appear brighter than any star in the night sky.


Look for Jupiter in the southeast about 30 minutes after sunset. Jupiter will set at 2:02 a.m. Those with a telescope can enjoy views of Jupiter’s cloud features and the Great Red Spot when it is pointed towards Earth.


Look for the ringed planet in the southeast about 30 minutes after sunset. Saturn sets at 2:43 a.m. For those with a telescope keep track of the orientation of Saturn’s rings. Since Saturn is tilted on its rotational axis, we cross the plane of Saturn’s ring every 13 to 15 years.  We are headed towards another ring plane crossing on March 23, 2025. Over the next five years you will notice Saturn’s rings will gradually incline towards an edge on appearance.

2020 Great Conjunction

This year the planets Jupiter and Saturn will reach conjunction.  A conjunction is when two or more celestial bodies share the same right ascension.  For Jupiter and Saturn this astronomical event occurs every 20 years. The conjunction occurs on December 21, 2020.  You will find the two planets close together in the southwest just after sunset on this date.

Visit the James S. McDonnell Planetarium for more information on what’s up!

Night Sky Update: September 4-September 12, 2020