This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, May 21, 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

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

May 26, 2021 Total Lunar Eclipse
Credit: Ernie Wright

This week a total lunar eclipse will occur in the early morning hours of May 26, 2021. A lunar eclipse occurs as the Moon passes through Earth’s shadow which is possible only if the Moon is at its full phase. It is also important to remember that when you have a lunar eclipse there will also be a solar eclipse. The two eclipses are separated by roughly two weeks because solar eclipse only occur when the Moon is at its new moon phase. So, on June 10, 2021 an annular solar eclipse will occur.

The June 10 solar eclipse will not be visible from St. Louis but the Lunar eclipse on May 26 will be. The eclipse begins on May 26 at 3:47 a.m. CDT. From this time until 4:44 a.m. CDT, The Moon will pass through the light part of Earth’s shadow called the penumbra. During this time little to no visible change will be noticed. After 4:44 a.m. CDT, the Moon will enter the dark core of Earth’s shadow called the umbra. As the Moon moves into this part of our shadow, the side we see from Earth will start to grow dark. Unfortunately, we will not see the Moon fully enter Earth’s umbral shadow because the Moon will set below the horizon before this occurs at 6:11 a.m. CDT.  By the time we see the Moon setting, it will be about 80% eclipsed.

To see this lunar eclipse, you will want to find as clear a view of the western horizon you can. If you do not find the early morning time agreeable, then you can wait until November this year when we will see another lunar eclipse. The November lunar eclipse occurs on November 19, 2021 and it will be a partial eclipse. You can find timings and graphics at https://www.timeanddate.com/eclipse/lunar/2021-may-26

The Sun and Moon


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

Sunrise is at 5:44 a.m. on Friday, May 21 and sunset is at 8:12 p.m. providing us with about 14 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for about 1 hour and 50 minutes. This period is called twilight, which ends around 10:02 p.m. this week. For those with a sundial, local noon occurs around 12:58 p.m. this week.

DaySunriseSunset
2021-05-21 5:44 a.m.8:12 p.m.
2021-05-22 5:44 a.m.8:13 p.m.
2021-05-23 5:43 a.m.8:13 p.m.
2021-05-24 5:42 a.m.8:14 p.m.
2021-05-25 5:42 a.m.8:15 p.m.
2021-05-26 5:41 a.m.8:16 p.m.
2021-05-27 5:41 a.m.8:16 p.m.
2021-05-28 5:40 a.m.8:17 p.m.
2021-05-29 5:40 a.m.8:18 p.m.

Moon 

Moonrise for Friday, May 21 occurs at 2:39 p.m. and moonset will occur at 3:31 a.m. on the following morning. On Friday, May 21 the Moon will exhibit a waxing gibbous phase with 71% of the lunar disk illuminated. Full moon for this month occurs on May 26 at 6:14 a.m. This month, there will also be a lunar eclipse on May 26. From St. Louis we will only see a partial eclipse occur because the Moon sets before it reaches totality. For more information, see the observing highlight section above.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of May 21 occur during evening hours. The best passes this week occur on the evenings of May 27 and 28. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, May 21

DateStartsMax. altitudeEnds
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
22 May-0.8 23:48:1410NNW 23:49:5416N 23:49:5416N
23 May-0.9 23:01:0610NNW 23:02:5313NNE 23:05:5512NE
24 May-1 23:49:3510NW 23:50:5319NNW 23:50:5319NNW
25 May-1.6 23:02:1610NNW 23:04:5323NNE 23:04:5323NNE
26 May-1.3 22:14:5710NNW 22:17:1717NNE 22:18:5413NE
26 May-0.9 23:51:0410NW 23:51:5016NW 23:51:5016NW
27 May-1 21:27:4010NNW 21:29:2613NNE 21:31:1210NE
27 May-2.3 23:03:3010NW 23:05:5037NNW 23:05:5037NNW
28 May-2.5 22:15:5910NW 22:19:0634NNE 22:19:5030ENE
29 May-1.8 21:28:3110NNW 21:31:1723NNE 21:33:5011E
29 May-1.9 23:04:5810WNW 23:06:4627WNW 23:06:4627WNW

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 www.heavens-above.com

Detailed information regarding all unmanned exploration of our universe, missions past, present, and planned, can be found at Jet Propulsion Laboratories:

http://www.jpl.nasa.gov/

The Visible Planets

Looking West, at 8:35 pm, May 21, 2021
Credit: Stellarium, EG, 

Looking Southeast, at 3:00 am, May 22, 2021
Credit: Stellarium, EG 

This week, five naked eye planets are visible. Mercury and Venus can be found in the west northwest just after sunset. Mars is found in the west after sunset. Jupiter and Saturn can be found in the southeast before sunrise.

Mercury

Mercury is past greatest elongation for the current evening apparition. Mercury is now head back towards the Sun as it heads towards inferior conjunction on June 10, 2021. Unfortunately, this means we will see less and less of Mercury each day. You can still look for Mercury about 30 minutes after sunset but each day the planet will be harder to find.

Venus

Venus is well into another evening apparition. By 8:30 p.m., Venus will be about 8° 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.

On May 28, 2021, Mercury and Venus will reach conjunction. Looking west on this date about 20 minutes after sunset, you will find Mercury and Venus separated by only 26 arc minutes. Mercury will be tough to see but Venus should be easy to spot. Once you spot Venus, keep watching this bright planet for another 10 minutes during which Mercury should become easier to find. For your best chance to see the pair of planets you will want to use binoculars but make absolute certain the Sun has set before you look. This conjunction will be the closest we see Mercury and Venus together until the year 2033.

Mars

Currently Mars appears as a 1.7-magnitude object that will be visible high in the west about 40 minutes after sunset. Mars sets by 11:38 p.m.

Jupiter

Jupiter is visible in the southeast before sunrise. Jupiter rises at 1:55 a.m. and will be easy to see in the southeast by 3:00 a.m.

Saturn

Saturn has returned to our morning sky. Saturn rises at 1:06 a.m. and will be easy to spot by 2:00 a.m. looking southeast

James S. McDonnell Planetarium

Night Sky Update: May 21-May 29, 2021