This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, July 31, 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.
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.
Sunrise is at 6:02 a.m. on Friday, July 31 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 just under 2 hours. This period is called twilight, which ends around 9:57 p.m. this week. For those with a sundial, local noon occurs around 1:07 p.m. this week.
|2020-07-31||6:02 a.m.||8:12 p.m.|
|2020-08-01||6:03 a.m.||8:11 p.m.|
|2020-08-02||6:04 a.m.||8:10 p.m.|
|2020-08-03||6:05 a.m.||8:09 p.m.|
|2020-08-04||6:06 a.m.||8:08 p.m.|
|2020-08-05||6:07 a.m.||8:07 p.m.|
|2020-08-06||6:08 a.m.||8:06 p.m.|
|2020-08-07||6:09 a.m.||8:04 p.m.|
|2020-08-08||6:09 a.m.||8:03 p.m.|
Moonrise for Friday, July 31 occurs at 6:13 p.m. and moonset will occur at 3:46 a.m. on the following day. On Friday, July 31 the Moon will exhibit a waxing gibbous phase with about 90% of the lunar disk illuminated. Full moon occurs on August 3 at 10:59 a.m. Full moon for August is often called the Full Sturgeon Moon.
International Space Station (ISS) Observing
Visible passes of ISS from St. Louis for the week of July 31 occur during evening hours. The best of these occur on the evenings of July 31 and August 3. Use the table below for information about these and other visible passes of ISS.
Catch ISS from St. Louis starting Friday, July 31
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:
The Visible Planets
Looking South, at 9:30 pm, July 31, 2020
Credit: Stellarium, EG
Looking East, 3:30 am, August 1, 2020
Credit: Stellarium, EG
This week, four naked eye planets are visible. Jupiter and Saturn rise before sunset. Look for them rising in the southeast once it is dark. Mars rises in the late evening and will be best seen after midnight. Venus can be found in the eastern sky before sunrise.
For those tracking Jupiter and Saturn as they approach their great conjunction later this year, the two gas giants currently appear about 7.7° apart in the sky. Jupiter appears to be moving away from Saturn right now due to retrograde motion. This is all an illusion caused by Earth passing by slower moving Jupiter. Saturn has also started retrograde motion. If you keep watching these planets as 2020 progresses, you will see some interesting behaviors that inspired early astronomers to track the skies.
Views of Mercury for the current morning apparition are ending. Mercury reached greatest elongation on July 22 and is now on its way back into the Sun’s glare. Superior conjunction occurs on August 17 after which we start an evening apparition. Unfortunately, the next evening apparition is not very good so it will be a while before we return to decent views of Mercury.
Venus is well into another morning apparition. After months of seeing Venus in the west after sunset Venus is now visible in the east before sunrise. Venus rises at 2:51 a.m. and will be easily seen by 3:30 a.m. Venus remains a morning object until March 26, 2021 when it reaches superior conjunction. Venus reaches maximum western elongation on August 12, 2020.
The red planet rises around 11:21 p.m. and will be high enough to see in the southeast by 12:00 a.m. Opposition for Mars occurs on October 13, 2020. As we head towards this date Mars will appear brighter and larger through a telescope improving surface details. Surface features are already visible when viewing conditions are favorable.
Look for Jupiter in the southeast about 30 minutes after sunset. Those with a telescope can enjoy views of Jupiter’s cloud features and the Great Red Spot when it is pointed towards Earth.
Look for the ringed planet in the southeast about 45 minutes after sunset. For those with a telescope keep track of the orientation of Saturn’s rings. Since Saturn is tilted on its rotational axis, we cross the plane of Saturn’s ring every 13 to 15 years. We are headed towards another ring plane crossing on March 23, 2025. Over the next five years you will notice Saturn’s rings will gradually incline towards an edge on appearance.
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 occurs every 20 years. The conjunction occurs on December 21, 2020. You will find the two planets close together in the southwest just after sunset on this date.
2020 Perseid Meteor Shower
The annual Perseid Meteor Shower is once again upon us. Every year starting around July 17 through August 26, the Earth moves through debris left by a comet named Comet Swift-Tuttle. This comet orbits the Sun every 133 years and was last seen in 1992. Meteor showers can persist for longer than some would expect, however their peak activity tends to be short. Even though a meteor shower can have active periods of a month, they tend to have very short peak periods of meteor activity. For the Perseids this peak period in 2020 occurs from about 10:00 p.m. on August 11 to sunrise on August 12. During peak time observers can expect 10 or 15 meteors per hour in light polluted skies and 100 meteors per hour from dark rural skies.
The key to observing any meteor shower is amount of time spent observing and awareness of the meteor shower’s radiant. Time is important because our eyes take time to adapt to darkness. The human eye will typically take about 40 minutes to become dark adapted. Additionally, when we talk about how many meteors you will see, it is meteors per hour. This means if you only step outside for 5 or 10 minutes you will be lucky if you see any meteors. It is ideal to spend at least an hour observing once your eyes have adapted. Knowledge of a meteor shower’s radiant is also important. This is the spot in the sky that meteors appear to come from. Think of driving into a snowstorm, all the snow appears to come from one spot in front of you. Same thing occurs during a meteor shower but instead of a car moving through snow, it is the Earth moving through debris in space. The radiant for the Perseids is in the constellation Perseus, which will be about 15° above the horizon on August 11 at 10:00 p.m. At this time, you will need to look northeast to see meteors because the radiant will be just above the northeastern horizon. As the night progresses, the Perseid radiant will climb higher in the sky. After midnight you will be able to see meteors moving in all directions emanating from the Perseid radiant.
This should be a decent year for the Perseids due to the Moon exhibiting a waning crescent phase with roughly 45% of the lunar disk illuminated. The moon rises at 12:19 a.m. so it should not interfere with views until early morning hours. Get to as dark a sky as you can, bring a comfortable chair that offers the best view of the entire sky and lastly sit back and relax and enjoy the show. Learn more about meteor showers at American Meteor Society
Comet C/2020 F3 (NEOWISE)
What has been the best comet in years is now fading and our opportunities to see it are beginning to end. As of July 29, the brightness of C/2020 F3 (NEOWISE) has faded to 5th magnitude. The comet is still visible through binoculars, but it will be come increasingly difficult to spot. The only thing that remains visible for light polluted observers is the comet’s coma as the tail has faded from view. C/2020 F3 (NEOWISE) remains high enough to see through the month of August, however, the comet’s magnitude is expected to drop to 10th magnitude by the end of August. Skilled comet observers will likely still be able to track the comet with telescopes, but it will likely fade from binoculars some time in August.
The declination of the comet is changing significantly each day and as such we will see it move from the northwest to southwestern skies throughout August. During August, the comet will move through the constellations Coma Berenices, Bootes and Virgo.
More information and detailed maps can be found here
Visit the James S. McDonnell Planetarium for more information on what’s up!
Night Sky Update: July 31-August 08, 2020