This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Tuesday, March 20. All times are given as local St. Louis time (Central Standard 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, April 6, 2018 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 7:04 a.m. on Tuesday, March 20 and sunset is at 7:13 p.m. providing us with about 12 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 8:42 p.m. this week. For those with a sun dial, solar transit or local noon occurs around 1:08 p.m. this week.

The Vernal Equinox occurs on March 20. This marks the beginning of spring. Once spring is here days will grow longer and nights will be shorter. The reason for this change is Earth’s axis of rotation is tilted about 23.5°. Due to this tilt the northern hemisphere is now becoming more inclined to the sun which in turn provides more direct exposure to the sun. The result of this is more daylight and warmer temperatures.




20 Mar

7:04 a.m.

7:13 p.m.

21 Mar

7:03 a.m.

7:14 p.m.

22 Mar

7:01 a.m.

7:15 p.m.

23 Mar

7:00 a.m.

7:16 p.m.

24 Mar

6:58 a.m.

7:17 p.m.

25 Mar

6:57 a.m.

7:18 p.m.

26 Mar

6:55 a.m.

7:19 p.m.

27 Mar

6:54 a.m.

7:20 p.m.

28 Mar

6:52 a.m.

7:21 p.m.

Moonrise for Tuesday, March 20 occurs at 9:07 a.m. and moonset will occur at 10:40 p.m. On Tuesday, March 20 the moon will be exhibiting a waxing crescent phase with about 1% of lunar disk illuminated. First quarter moon occurs on March 24.

International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of March 20 occur in the morning and evening hours. The best of these occur on the evenings of March 23, 25 and 26. Use the table below for information about these and other visible passes of ISS this week.

Catch ISS flying over St. Louis starting Tuesday, March 20



Max. altitude


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

20 Mar

-2.5 05:09:02 38 ESE 05:09:02 38 ESE 05:11:11 10 ESE

21 Mar

-2.2 05:52:27 20 SSW 05:52:27 20 SSW 05:54:19 10 S

23 Mar

-3.8 20:44:20 10 SW 20:47:26 60 SSE 20:47:26 60 SSE

24 Mar

-2.9 19:52:31 10 SSW 19:55:24 29 SE 19:58:19 10 ENE

24 Mar

-1.6 21:58:57 10 W 21:31:05 26 WNW 21:31:05 26 WNW

25 Mar

-3.0 20:36:19 10 WSW 20:39:31 51 NW 20:41:45 18 NE

26 Mar

-3.9 19:43:57 10 SW 19:47:13 80 SE 19:50:30 10 NE

26 Mar

-1.2 21:21:48 10 WNW 21:24:03 17 NNW 21:24:52 16 N

27 Mar

-1.7 20:28:46 10 W 20:31:33 25 NNW 20:34:20 10 NNE

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 all five naked eye planets will be visible. Mercury and Venus are in evening apparitions while Mars, Jupiter and Saturn remain best in the early morning.


The elusive planet Mercury reached greatest eastern elongation on March 15. Unfortunately this means we will soon lose Mercury to the glare of the sun. Around 7:40 p.m. at the start of this week you will find Mercury about 10° above the western horizon. By the end of the week it will be difficult to find Mercury in the twilight glow of the sun.


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 10° above the western horizon around 7:40 p.m. Those with a clear western horizon should be able to see Venus soon after sunset low in the west.

The evening apparition of Venus that is starting will last all the way through October 2018. So for 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.


The red planet has started another apparition and can be found rising in the east by 2:36 a.m. Mars will be visible low in the east around 4:00 a.m. Each week Mars will rise a little earlier than the week before as we approach the 2018 Mars opposition which occurs on July 27.

If you want to start preparing for the upcoming 2018 Mars opposition follow this link:


TThe king of the planets can be found rising by 11:26 p.m. but can be easily seen by 1:00 a.m. low in the east. Jupiter will slowly elongate away from the Sun reaching opposition on May 8, 2018.

Saturn has been slowly climbing out of the Sun’s glare for some time now, however, the angle of the ecliptic in the early morning has kept the ringed planet low. Saturn is now rising by 3:02 a.m. and will be an easy target by 4:00 a.m.

Our next Star Party will be held on Friday, April 6, 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 April 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 begin 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.