This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, April 17, 2020.

Information updated weekly or as needed.

Times given as local St. Louis time (CDT).  For definitions of terminology used in the night sky update, click the highlighted text.

For now, star parties at the Saint Louis Science Center have 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.

The Sun and Moon

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

Sunrise is at 6:21 a.m. on Friday, April 17 and sunset is at 7:40 p.m. providing us with about 13.5 hours of daylight.  Even after sunset, the light from the Sun will dimly illuminate our sky for a little over 1.5 hours.  This period is called twilight, which ends around 9:16 p.m. this week.  For those with a sundial, solar transit or local noon occurs around 1:01 p.m. this week.

2020-04-176:21 a.m.7:40 p.m.
2020-04-18 6:20 a.m.7:41 p.m.
2020-04-196:19 a.m.7:42 p.m.
2020-04-20 6:17 a.m.7:43 p.m.
2020-04-21 6:16 a.m.7:44 p.m.
2020-04-226:15 a.m.7:45 p.m.
2020-04-23 6:13 a.m.7:46 p.m.
2020-04-24 6:12 a.m.7:47 p.m.
2020-04-25 6:11 a.m.7:48 p.m.

Moonrise for Friday, April 17 occurs at 4:10 a.m. and moonset will occur at 2:41 p.m. On Friday, April 17 the Moon will be exhibiting a waning crescent phase with roughly 21% of the lunar disk illuminated. New moon occurs on April 22.


International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of April 17 occur during morning hours. Use the table below for information about these and other visible passes of ISS.

DateMagStarts  Max. altitude  Ends  
24 Apr-1.5 05:18:1610S 05:20:4820SE 05:23:2110E
25 Apr-1 04:32:3610SSE 04:33:4711SE 04:34:5810ESE

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 Visible Planets

Looking West, 8:00 pm, April 17, 2020
Credit: Stellarium, EG

Looking Southeast, 4:00 am, April 18, 2020
Credit: Stellarium, EG

This week, four naked eye planets are visible. Venus will be visible in the west just after sunset.  Mars, Jupiter and Saturn are visible in the southeast about 2.5 hours before sunrise.


The brightest planet in the sky is visible in the western sky as the sun sets. Venus reached maximum elongation for its current apparition; because of this Venus will start to move towards the Sun each night as it approaches inferior conjunction on June 3, 2020. Venus will set around 11:26 p.m.


The red planet rises around 3:18 a.m. and will be high enough to see in the southeast by 4:00 a.m. Opposition for Mars occurs on October 13, 2020.  As we head towards this date Mars will appear brighter and its surface will eventually be visible through a telescope.


The king of the planets is rising around 2:21 a.m. and should be visible in the southeast around 3:30 a.m. Each week you will find Jupiter rising about 30 minutes earlier than it did in the previous week.


Saturn is rising around 2:39 a.m.  Like Jupiter you will need a clear sky to the southeast to catch the ring planet around 3:30 a.m.  Later this year Jupiter and Saturn will reach conjunction on December 21, 2020.  You can track these planets as they appear to chase one another throughout the rest of this year.

2020 Great Conjunction

This year, the planets Jupiter and Saturn will reach conjunction.  A conjunction is when two or more celestial bodies share the same right ascension.  For Jupiter and Saturn, this astronomical event only occurs every 20 years. The conjunction will occur on December 21, 2020.  You will find the two planets close together in the southwestern sky just after sunset on this date.

Comet C/2019 Y4 ATLAS

Credit: NASA/JPL

Comet C/2019 Y4 ATLAS was discovered in images from a robotic telescope survey called ATLAS (Asteroid Terrestrial-impact Last Alert System).  This instrument consists of two 0.5-meter telescopes that each clear night observes a quarter of the observable sky looking for moving objects. The intention is to identify Near-Earth Objects (NEOs). Currently this survey has discovered 430 Near-Earth Asteroids, 44 Potentially Hazardous Asteroids, 37 Comets and 5464 Supernovae.  Supernovae are not what would be considered moving objects but are a bonus science objective the program contributes to.

Many northern hemisphere observers are hopeful that Comet C/2019 Y4 ATLAS will become our next great comet.  Unfortunately, it is difficult to predict how bright comets will become. Over the past few decades there have been comets that received great hype but turned out to be duds. One of the best examples from recent times is Comet ISON or C/2012 S1. This was a sun grazing comet that was predicted to possibly be as bright as the full moon after its perihelion.  Unfortunately, the comet disintegrated and never became the bright comet observers hoped for. It may be exciting to hear the C/2019 Y4 ATLAS could reach -5 magnitude but remember this is just a possibility.

UPDATE for C/2019 Y4 ATLAS April 10, 2020

Comet C/2019 Y4 ATLAS continues to get fainter and is now being reported at 9.5 magnitude. In early April astronomers noted a distinct change in the comet’s appearance. Initially C/2019 Y4 ATLAS’s core looked more compact until April when it has changed to a more elongated fuzzy appearance.  This suggests the comet has fragmented. This doesn’t mean the comet will not be the naked eye object we are hoping for, but it doesn’t look good. With the continued fade it appears this comet will under perform.  It is still worth tracking it as it approaches its flyby of the Earth on May 23.

In dark skies C/2019 Y4 ATLAS is still within reach of backyard telescopes 6 inches and larger, however, in the city lights of St. Louis it will be very difficult to see. Current attempts to locate the comet by this author have been unsuccessful due to light pollution.  As we head towards Comet C/2019 Y4 ATLAS’s closest approach to Earth on May 23, 2020, we will continue to update the current magnitude of this comet in the night sky update.

Comet SWAN (C/2020 F8)

With what seems to be another comet let down, there is hope for comet hunters. A new comet was recently discovered by Michael Mattiazzo searching imagery from the Solar Wind Anisotropies (SWAN) camera on the Solar and Heliospheric Observatory (SOHO). SWAN’s primary science objective has to do with monitoring the solar wind in Lyman-α light, a type of UV radiation. It also monitors sunspots and can also observe comets in this same emitted wavelength of light. Learn more at

Right now, Comet SWAN is only visible in the southern hemisphere, but it will be visible in the northern hemisphere near the end of April. Currently Comet SWAN is 8th magnitude, but it is predicted to reach 3.5 magnitude in the last half of May. The behavior of comets is unpredictable and as such predictions of future magnitudes is never a guarantee. That being said, this will be a comet to keep track of.

If you would like to learn more about the potential breakup of Comet C/2019 Y4 ATLAS or the new Comet SWAN (C/2020 F8) visit


Visit the James S. McDonnell Planetarium for more information on what’s up!

Night Sky Update: April 17-April 25, 2020