This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, September 11. All times are given as local St. Louis time (Central Daylight Time). For definitions of terminology used in the night sky update, click the highlighted text.

Information updated weekly or as needed.

Join us for our next star party, Friday, October 5, 2018 held in association with the St. Louis Astronomical Society. For details, see the information at the bottom of this page.

The Sun and Moon

Sunrise is at 6:39 a.m. on Tuesday, September 11 and sunset is at 7:15 p.m. providing us with about 13 hours of daylight. Even after sunset, the light from the sun will still dimly illuminate our sky for about 1.5 hours. This period of time is called twilight, which ends around 8:46 p.m. this week. For those with a sun dial, solar transit or local noon occurs around 12:58 p.m. this week.




11 Sep

6:39 a.m.

7:15 p.m.

12 Sep

6:40 a.m.

7:14 p.m.

13 Sep

6:41 a.m.

7:12 p.m.

14 Sep

6:42 a.m.

7:11 p.m.

15 Sep

6:43 a.m.

7:09 p.m.

16 Sep

6:43 a.m.

7:07 p.m.

17 Sep

6:44 a.m.

7:06 p.m.

18 Sep

6:45 a.m.

7:04 p.m.

19 Sep

6:46 a.m.

7:03 p.m.

Moonrise for Tuesday, September 11 occurs at 8:39 a.m. and moonset will occur at 8:49 p.m. On Tuesday, September 11 the moon will be exhibiting a waxing crescent phase with roughly 5% of the lunar disk illuminated. First quarter moon occurs on September 16.

International Space Station (ISS) Observing

Visible passes of ISS from St. Louis for the week of September 11 occur during morning hours. The best of these occur on the mornings September 15 and 17. Use the table below for information about these and other visible passes of ISS this week.

Catch ISS from St. Louis starting Tuesday, September 11



Max. altitude


Time Alt. Az. Time Alt. Az. Time Alt. Az.

11 Sep

-1.1 06:00:37 10 NNW 06:02:49 16 NNE 06:04:59 10 ENE

13 Sep

-1.9 05:52:42 10 NNW 05:55:36 28 NNE 05:58:29 10 E

14 Sep

-1.2 05:01:03 10 NNW 05:03:26 19 NNE 05:05:50 10 ENE

15 Sep

-0.7 04:11:36 13 NNE 04:11:36 13 NNE 04:12:56 10 NE

15 Sep

-3.4 05:44:56 10 NW 05:48:11 63 NE 05:51:26 10 ESE

16 Sep

-2.3 04:55:04 27 N 04:56:06 34 NNE 04:59:07 10 E

17 Sep

-0.5 04:06:01 13 ENE 04:06:01 13 ENE 04:06:32 10 E

17 Sep

-3.6 05:38:46 22 WNW 05:40:34 47 SW 05:43:42 10 SSE

18 Sep

-2.3 04:49:58 31 SE 04:49:58 31 SE 04:51:49 10 SE

19 Sep

-1.7 05:34:10 14 SSW 05:34:10 14 SSW 05:35:02 10 S

19 Sep

-1.4 20:32:35 10 SSW 20:33:05 13 S 20:33:05 13 S

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 Planets Visible Without a Telescope

This week four of the naked eye planets are visible. Venus is in the west after sunset, Jupiter is visible after sunset in the southwest, Saturn is in the south a little after sunset and Mars will be seen shortly after sunset in the southeast.


The second planet from the sun is climbing out of the sun’s glare. Typically the 30 minute mark after sunset is what we use to determine if a planet is visible yet. Using this approach Venus will be about 8.4° above the western horizon around 7:45 p.m.

The evening apparition of Venus that is underway will last most of the way through October 2018. Most of the year Venus will be an early evening target. Another observing note is that Venus will start in a gibbous phase and end this apparition in a crescent phase. Planets that are closer to the sun than we are exhibit phases like the moon does. As the apparition progresses Venus will grow brighter because it will be getting closer to Earth. On October 26 Venus will reach inferior conjunction which is when Venus passes between the Earth and Sun.

Venus and Mercury both exhibit phases like the moon does. This is due to them being closer to the Sun than Earth is. This is also why we only see these planets just after sunset or just before sunrise. Venus is exhibiting a quarter phase with about 37° of the disk of Venus illuminated. This will decrease as the year goes on. Small telescopes and large binoculars will reveal the phases of Venus.


The red planet can be found rising in the southeast by as the sun sets. Due to trees and buildings Mars will be best seen after 9:00 p.m. Mars will set by 2:24 a.m.


The king of the planets rises before the sun sets. Start looking for it in the southwest about 30 minutes after sunset. Jupiter will set by 9:47 p.m.


Saturn has been visible in the southern sky for some time now but the angle of the summertime ecliptic has kept the ringed planet low in the southern sky. Saturn now rises before sunset so if you have a clear southern sky you should be able to spot Saturn by 8:30 p.m. Saturn sets at 12:32 a.m.

Our next Star Party will be held on Friday, October 5, 2018, from dusk until 10 p.m.

As part of the Saint Louis Science Center’s First Fridays, weather permitting, the St. Louis Astronomical Society and the 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 October 5, join us indoors in our planetarium theater for “The Sky Tonight”. Showtime is at 7 p.m.

This free, indoor star program will introduce you to the current night sky, the planets, and the seasonal constellations. Doors open 15 minutes before show time. Shows begins at 7 p.m. Sorry, no late admissions due to safety issues in the darkened theater.

The St. Louis Astronomical Society helps host the monthly Star Parties at the Saint Louis Science Center which are held on the first Friday of each month. Our Monthly Star Parties are open to the public and free of charge. Telescope viewing is scheduled to start around 7:00 p.m. however with the change to day light saving time, darkness starts closer to 8:00 p.m.