This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, September 12.  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 6, 2017 held in association with the St. Louis Astronomical Society.  For details, see the information at the bottom of this page.

The Sun and the Moon

Sunrise is at 6:40 a.m. on Tuesday, September 12 and sunset is at 7:13 p.m. providing us with a little more than 12 hours of daylight.  Even after sunset, the light from the sun will still dimly illuminate our sky for a bit less than 2 hours.  This period of time is called twilight, which ends around 8:44 p.m. this week.  For those with a sun dial, solar transit or local noon occurs around 12:57 p.m. this week.


Day Sunrise Sunset
 12 Sep 6:40 a.m. 7:13 p.m.
 13 Sep 6:41 a.m. 7:12 p.m.
 14 Sep 6:42 a.m. 7:10 p.m.
 15 Sep 6:43 a.m. 7:09 p.m.
 16 Sep 6:44 a.m. 7:07 p.m.
 17 Sep 6:45 a.m. 7:05 p.m.
 18 Sep 6:45 a.m. 7:04 p.m.
 19 Sep 6:46 a.m. 7:02 p.m.
 20 Sep 6:47 a.m. 7:01 p.m.


Moonrise for Tuesday, September 12 occurs at 11:48 p.m. and moonset will occur at 2:25 p.m. on the following day.  On Tuesday, September 12 the moon will be exhibiting a waning gibbous phase with about 57% of the lunar disk illuminated.  Last quarter moon occurs on September 13.


International Space Station (ISS) Observing

Visible passes of ISS from St. Louis for the week of September 12 occur in the morning hours.  The best of these occur on the mornings of September 19 and 20.  Use the table below for information about these and other visible passes of ISS this week.

Catch ISS flying over St. Louis starting Tuesday, September 12


Mag Starts Max. altitude Ends
Time Alt. Az. Time Alt. Az. Time Alt. Az.
15 Sep -1.5 06:05:34 10 NNW 06:08:15 22 NNE 06:10:55 10 E
16 Sep -1.0 05:13:34 10 NNW 05:15:40 16 NNE 05:17:46 10 ENE
17 Sep -2.7 05:57:00 10 NW 06:00:10 43 NNE 06:03:20 10 ESE
18 Sep -1.7 05:05:43 15 NNW 05:07:41 26 NNE 05:10:30 10 E
19 Sep -0.8 04:16:04 16 NE 04:16:04 16 NE 04:17:24 10 ENE
19 Sep -3.9 05:48:45 11 NW 05:51:54 75 SW 05:55:10 10 SE
20 Sep -3.2 04:59:18 53 NNE 04:59:30 54 NE 05:02:43 10 ESE


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


The elusive planet Mercury has started another morning apparition that will last from September 4 to September 28.  The best chance to catch Mercury will be this week.  Mercury will reach greatest western elongation on September 12.  To find Mercury you will want to go out before civil twilight begins and find yourself a clear view of the eastern horizon.  Civil twilight this week starts around 6:00 a.m. so your best window to see Mercury will be around 5:45 a.m.


The second planet from the sun can be found in the morning hours just before sunrise. Your best shot to see Venus is to find a clear eastern horizon view around 5:00 a.m.  Be careful though as you will be fighting the rising sun’s twilight glow.


The king of the rings is visible once again.  You can find it at 8:30 p.m. by looking to the south.  Saturn will set by 11:38 p.m.


Our next Star Party will be held on Friday, October 6, 2017, 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 6, 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.