This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, May 14, 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

Constellation Corona Borealis Seen in the East After Sunset
Credit: Stellarium, EG

Over the next few months, we will look at some of the smaller lesser-known constellations. This week, we’re highlighting the constellation Corona Borealis. Also known as the Northern Crown, Corona Borealis is the 73rd largest constellation, covering about 0.43% of the sky. It is one of the 48 constellations recorded by Ptolemy and is attributed to the Greek story of a wreath given to the Cretan Ariadne by the god Dionysus. Corona Borealis is found between the constellations Boötes and Hercules, appearing as a U-shape of stars. The brightest stars in the crown are 4th magnitude, except for the alpha star named Alphecca, which appears as a 2.23 magnitude star.

Being so small, Corona Borealis does not have many easy targets to hunt down. The most interesting targets of interest are variable stars, which are stars that fluctuate in magnitude. (For those new to variable stars, the best place to learn about them is the American Association of Variable Star Observers.) Some have regular periods of fluctuation while others are irregular, and some are cataclysmic. For a basic rundown on variable star types, read this AAVSO article.

The variable star in this week’s highlight is an unpredictable variable star that has a history of close observation due to drastic changes in its magnitude. The star in question is the variable star R Coronae Borealis (R CrB). This star usually shines at 6th magnitude, making it an easy target for binocular viewers. In the past, this star has suddenly—within a few weeks—dropped down to 14th magnitude before eventually returning to its normal magnitude. This dimming is caused by a dust cloud that obscures the photosphere of the star.

Discovered more than 200 years ago, R CrB is the prototype star of a type of eruptive variable star that shares its name. They are rare hydrogen poor stars that are high in helium and carbon. They are F and G-type supergiants thought to be the result of a merger between two intermediary-sized white dwarf stars.

Observation of all types of variable stars by amateur astronomers is critical to help astronomers better understand these fascinating stellar objects. There are simply too many for professional astronomers to constantly monitor. Variable star astronomy is a great example of where amateur astronomers are making serious contributions to the field. R CrB will not put on a show every night, but it is a target worth returning to each night it is visible to see if you can catch it in its next fluctuation. If variable stars seem like the type of target you are interested in, the constellation Corona Borealis has several other examples. A few of interest are the cataclysmic variable T Coronae Borealis and the long-period variable S Coronae Borealis.

It is easy to overlook the smaller constellations of the sky. They may not have as many targets that beckon us, but they often offer us great targets worth our observing time.

The Sun and Moon


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

Sunrise is at 5:50 a.m. on Friday, May 14, and sunset is at 8:06 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 45 minutes. This period is called twilight, which ends around 9:53 p.m. this week. For those with a sundial, local noon occurs around 12:58 p.m. this week.

DaySunriseSunset
2021-05-14 5:50 a.m.8:06 p.m.
2021-05-15 5:49 a.m.8:06 p.m.
2021-05-16 5:48 a.m.8:07 p.m.
2021-05-17 5:47 a.m.8:08 p.m.
2021-05-18 5:47 a.m.8:09 p.m.
2021-05-195:46 a.m.8:10 p.m.
2021-05-20 5:45 a.m.8:11 p.m.
2021-05-21 5:44 a.m.8:12 p.m.
2021-05-22 5:44 a.m.8:13 p.m.

Moon 

Moonrise for Friday, May 14 occurs at 7:38 a.m., and moonset will occur at 11:02 p.m. On Friday, May 14, the Moon will exhibit a waxing crescent phase with 8% of the lunar disk illuminated. First quarter moon occurs on May 19 at 2:13 p.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of May 14 occur during morning and evening hours. The best passes this week occur on the mornings of May 15 and 16 and on the evenings of May 14 and 15. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, May 14

DateStartsMax. altitudeEnds
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
14 May-3.4 21:59:5110WSW 22:03:1166NW 22:06:3310NE
14 May-0.5 23:38:3410NW 23:40:3114NNW 23:42:2910NNE
15 May-0.7 02:54:1010NNW 02:56:2917NNE 02:58:4810ENE
15 May-3.9 04:30:1710NW 04:33:4086SW 04:37:0210SE
15 May-3.9 21:12:2610SW 21:15:4569SE 21:19:0610NE
15 May-0.9 22:50:2310WNW 22:52:5219NNW 22:55:2010NNE
16 May-3 03:42:5310NW 03:46:1354NE 03:49:3110ESE
16 May-1.4 22:02:2210W 22:05:1526NNW 22:08:0910NNE
17 May-1.5 03:00:1222E 03:00:1222E 03:01:4810E
17 May-2.8 04:33:4417W 04:35:2526SW 04:38:1610S
17 May-2.2 21:14:3210WSW 21:17:4139NNW 21:20:5310NE
18 May-0.6 22:05:3510NW 22:07:3214NNW 22:09:2810NNE
19 May-0.8 21:17:2410WNW 21:19:5119NNW 21:22:2010NNE
22 May-0.8 23:48:0710NNW 23:49:4616N 23:49:4616N

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 8:30 pm, May 14, 2021
Credit: Stellarium, EG, 

Looking Southeast, at 3:30 am, May 15, 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 starting another evening apparition. The elusive planet will remain visible in the west through most of May. Mercury will reach greatest eastern elongation on May 17. After this we will see Mercury less and less each day as it heads towards inferior conjunction on June 10, 2021. Look for Mercury in the west northwest about 30 minutes after sunset.

Venus

Venus is starting another evening apparition. It is still a little too close to the Sun to see easily see but with a clear view to the west northwest you might catch a glimpse of Venus about 20 minutes after sunset. Make sure the Sun has set before trying to find Venus this week.

Mars

Currently Mars appears as a 1.6-magnitude object that will be visible high in the west about 40 minutes after sunset. Mars sets by 11:51 p.m.

Jupiter

Jupiter is visible in the southeast before sunrise. Jupiter rises at 2:24 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 1:37 a.m. and will be easy to spot by 2:30 a.m. looking southeast.

James S. McDonnell Planetarium

Night Sky Update: May 14-May 22, 2021