This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, March 19, 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

Zodiacal Light
Credit: ESO/Y. Beletsky

Now that Spring is upon us, it is time to start looking for the zodiacal light. The zodiacal light is produced as sunlight reflects off interplanetary dust that is between Earth and just beyond Mars. It appears as a faint luminous glow that exhibits a cone shape. The cone starts at the horizon extending along the ecliptic. The path of the ecliptic is the plane of Earth’s orbit and it is what defines a constellation as zodiacal. Being found along this path in the sky is why it is called the zodiacal light. Zodiacal light is best seen when the angle between the ecliptic and horizon are steep. For northern hemisphere observers this occurs after sunset in the spring and before sunrise in the fall.

Your best chance to see the zodiacal light right now is to first go somewhere dark. The light pollution of metropolitan areas will keep you from seeing the zodiacal light. As it is spring you will want to look west about 1-hour after sunset. Being dark adapted and using averted vision will increase your chance of seeing this faint display.

It has long been thought that the dust that scatters sunlight resulting in the zodiacal light was produced by comets and asteroids. Recently, scientists that are part of NASA’s Juno mission discovered this interplanetary dust might come from a different source. That source is the planet Mars. As Juno was traveling towards Jupiter, instruments on the spacecraft observed particles near Juno that were a surprise. What they would come to find is dust grains were smashing into the Juno spacecraft at speeds of 10,000 mph and were chipping off small pieces of the spacecraft’s solar panels. It is these small pieces of Juno that were being detected by star tracking cameras that are part of Juno’s magnetometer investigation. Tracking the paths of these dust particles striking Juno resulted in a determination that they orbit the Sun between the Earth and about 2 AU from the Sun. Further modeling their orbits, the Juno scientists found that the likely source of the dust was not comets and asteroids but instead the planet Mars. One possible method for this dust production could be the global wide dust storms that occur on Mars. For a more detailed look at these new findings visit https://www.nasa.gov/feature/goddard/2021/serendipitous-juno-spacecraft-detections-shatter-ideas-about-origin-of-zodiacal-light

The Sun and Moon


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

Sunrise is at 7:06 a.m. on Friday, March 19 and sunset is at 7:12 p.m. providing us with roughly 12 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for about 1 hour and 40 minutes. This period is called twilight, which ends around 8:41 p.m. this week. For those with a sundial, local noon occurs around 12:09 p.m. this week.

2021-03-19 7:06 a.m.7:12 p.m.
2021-03-20 7:04 a.m.7:13 p.m.
2021-03-21 7:03 a.m.7:14 p.m.
2021-03-22 7:01 a.m.7:15 p.m.
2021-03-23 6:59 a.m.7:16 p.m.
2021-03-24 6:58 a.m.7:17 p.m.
2021-03-25 6:56 a.m.7:18 p.m.
2021-03-266:55 a.m.7:19 p.m.
2021-03-27 6:53 a.m.7:20 p.m.

Vernal Equinox March 20, 2021

Sun at Local Noon on the Summer Solstice 2020 and Vernal Equinox 2021
Credit: Eric Gustafson

On March 20, 2021 at 4:37 a.m. the Sun’s apparent path will cross the celestial equator at its ascending node. This day is called the Vernal Equinox and it marks the start of astronomical spring. After March 20, the Sun will climb higher in the sky each day. This results in longer daytime hours and shorter nighttime hours. This behavior will continue as we head towards the summer solstice in June.

Earth’s axial tilt is the reason the Sun appears to get higher in the sky each day as we move towards summer. Earth’s axis of rotation is tilted 23.5° with respect to our orbital plane. As we revolve around the Sun this tilt causes the northern and southern hemispheres to have an annual variance in exposure to direct sunlight. This drives our seasonal fluctuations in temperature and weather. Spring and summer are the warmer seasons as the Sun appears to climb higher in the sky increasing hours of daytime. Fall and winter are the cooler seasons as the Sun appears lower in the sky leading to shorter hours of daytime.

Moon 

Moonrise for Friday, March 19 occurs at 6:18 a.m. and moonset will occur at 5:28 p.m. On Friday, March 19 the Moon will exhibit a waxing crescent phase with 35% of the lunar disk visible. First quarter moon occurs on March 21 at 9:40 a.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of March 19 occur during morning and evening hours. The best passes this week occur on the evenings of March 20 and 22. Use the table below for information about these and other visible passes this week.

Catch ISS from St. Louis starting Friday, March 19

DateStartsMax. altitudeEnds
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
20 Mar-3.7 19:37:5010SW19:41:1182NW19:44:3410NE
21 Mar-1.4 20:28:1410WNW20:30:5321NNW 20:33:3210NNE
22 Mar-1.9 19:40:2210W19:43:2230NNW 19:46:2310NNE
24 Mar-1.119:43:3810WNW19:45:4716NNW 19:47:5610NNE

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 8:00 pm, March 20, 2021
Credit: Stellarium, EG, 

Looking East Southeast, at 6:00 am, March 21, 2021
Credit: Stellarium, EG 

This week, three naked eye planets are visible. Mars is found high in the west after sunset. Jupiter and Saturn can be found in the east southeast before sunrise.

Mars

Currently Mars appears as a 1.1-magnitude object that will be visible high in the west about 40 minutes after sunset. Mars sets by 12:58 a.m.

Jupiter 

Jupiter is starting to climb out of the Sun’s glare just before sunrise. For your best chance to see Jupiter, look east southeast 40 minutes before sunrise. 

Saturn 

Saturn has returned to our morning sky. Look east southeast 1 hour before sunrise to find the ringed planet.

James S. McDonnell Planetarium

Night Sky Update: March 19-March 26, 2021