This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, August 27, 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

With the changing recommendations from the CDC regarding COVID-19, conversations regarding the return of star parties at the Saint Louis Science Center have begun. We are close to bringing back our public telescope viewings, but a few details still need to be worked out. We will post future updates as we learn more about when we can bring back telescope viewings.

Observing Highlight of the Week

Fomalhaut is a star thought to have a forming planetary system.
Simulated sky created using Stellarium. Fomalhaut image credit: NASA/ ESA/ A. Gáspár/ G. Rieke (University of Arizona)

This week, we will look for the bright A-class star Fomalhaut. Fomalhaut starts to rise in the southeast this week around 10 p.m. Due to its southern declination, Fomalhaut will only be seen in the south from St. Louis, reaching its highest altitude around 1:30 a.m. It is the brightest star in the constellation Piscis Austrinus with a visual magnitude of 1.17. This makes it the 18th brightest star we see at night. It is 25 light years away and thought to be roughly 440 million years old.

Fomalhaut has long been a star of interest for several reasons. In 1983, the IRAS satellite detected a higher amount of infrared radiation from Fomalhaut than expected. It 1998, a disk-like structure was imaged around Fomalhaut, indicating it had a circumstellar disk and was developing planetary system. Through continued observations, Fomalhaut was found to have several disk-like structures, some with distinct edges that suggest it may have large planetary bodies.

In 2008, the Hubble telescope observed what appeared to be a planet orbiting the star. Subsequent observations continued to support the idea that the object was orbiting Fomalhaut, and it was named Fomalhaut b. Scientists observed Fomalhaut b expanding and dimming. This suggested that instead of a planet, Fomalhaut b is likely an expanding dust cloud. If this is the case, Fomalhaut b was likely the result of two planetesimals colliding. This type of event is estimated to occur once every 200,000 years.

Whereas it initially seems disappointing that Fomalhaut b is not a planet, it still supports the idea that Fomalhaut is a forming planetary system. The debris belts found around this star are similar to structures like the asteroid belts and Kuiper belt of our solar system. With sharp, defined edges, it also indicates there could still be planets orbiting Fomalhaut that have not yet been seen. Fomalhaut offers us a chance to see what our solar system was like when it was forming.

Fomalhaut is easy to find as it is the only bright star in the southern fall sky. The easiest way to find the star in 2021 will be to locate Jupiter and Saturn. Both planets can be found in the southeast about 30 minutes after sunset. Jupiter and Saturn will be the brightest objects you see in that part of the sky, but you can confirm you have found them as stars twinkle and planets usually do not. Fomalhaut rises around 9:30 p.m. and should clear trees and buildings around 10:30 p.m. Once Fomalhaut is high enough to see, it will be the brightest object about 20° south of Jupiter.

As we learn to observe the night sky objects like the Moon, the planets or deep sky objects tend to take center stage. Stars are often overlooked because they appear to many as just points of light. However, with context, many stars are fascinating to learn about and observe. Whether it be a variable star, a multiple star system, or the color of stars, learning about and observing stars are worth your time.

The Sun and Moon


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

Sunrise is at 6:26 a.m. on Friday, August 27, and sunset is at 7:38 p.m., providing us with a bit over 13 hours of daylight. Even after sunset, the light from the Sun will dimly illuminate our sky for roughly 1 hour and 30 minutes. This period is called twilight, which ends around 9:12 p.m. this week. For those with a sundial, local noon occurs around 1:03 p.m. this week.

DaySunriseSunset
2021-08-27 6:26 a.m.7:38 p.m.
2021-08-28 6:27 a.m.7:36 p.m.
2021-08-29 6:28 a.m.7:35 p.m.
2021-08-30 6:28 a.m.7:33 p.m.
2021-08-31 6:29 a.m.7:32 p.m.
2021-09-01 6:30 a.m.7:30 p.m.
2021-09-02 6:31 a.m.7:29 p.m.
2021-09-03 6:32 a.m.7:27 p.m.
2021-09-04 6:33 a.m.7:26 p.m.

Moon 

Moonrise for Friday, August 27 occurs at 10:31 p.m. and moonset will occur at 12:31 p.m. on the following day. On Friday, August 27 the Moon will exhibit a waning gibbous phase with about 74% of the lunar disk illuminated. last quarter moon occurs on August 30 at 2:13 a.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of August 27 occur during morning hours. The best pass this week occurs on the morning of August 29. Use the table below for information about this and other visible passes this week.

Catch ISS from St. Louis starting Friday, August 27

DateStartsMax. altitudeEnds
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
28 Aug-0.7 03:40:2315ENE 03:40:2315ENE 03:41:0510ENE
28 Aug-2.2 05:13:2319WNW 05:14:4926NNW 05:17:4410NNE
29 Aug-2.5 04:28:1835N 04:28:1835N 04:30:5510NE
30 Aug-0.7 03:43:1017NE 03:43:1017NE 03:44:0110NE
30 Aug-1.3 05:16:0910NW 05:18:0214NNW 05:19:5910NNE
31 Aug-1.5 04:31:0018NNW 04:31:0018NNW 04:33:1710NNE
01 Sep-0.6 03:45:4914NNE 03:45:4914NNE 03:46:3110NNE

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 South, at 8:00 p.m. August 27, 2021
Credit: Stellarium, EG 

Looking South, at 3:00 am, August 28, 2021
Credit: Stellarium, EG 

This week, three naked eye planets are visible. Venus can be found in the west after sunset. Jupiter and Saturn can be found in the southeast by 9:00 p.m.

Mercury

Mercury has started another evening apparition but this one will be tough. Even though Mercury is bright enough to see naked eye, it never strays far from the Sun. Additionally, the angle of the ecliptic we see at sunset right now is decreasing meaning even when Mercury reaches maximum elongation, on September 13, 2021, it will not be seen very high above the horizon. Anyone with a clear western horizon might peak a view of Mercury 20 minutes after sunset. It will likely require binoculars but if you attempt this make absolute sure the Sun has set.

Venus

Venus is well into another evening apparition. By 8:00 p.m., Venus will be about 13° above the western horizon. Venus will set at 9:08 p.m. As 2021 continues, Venus will continue to elongate from the Sun 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.

Jupiter

Jupiter has passed opposition and as such will be visible about 30 minutes after sunset. Look for Jupiter in the southeast as it starts to darken outside. Jupiter sets at 5:41 a.m. tomorrow morning and will set about 30 minutes earlier each week. Jupiter reaches superior conjunction on March 5, 2022. This means we can count on seeing Jupiter in the south for the rest of this year and well into 2022.

Saturn

Saturn is past opposition which means it will be visible about 30 minutes after sunset. Right now, it can be found in the southeast after sunset, but as we continue through the year, Saturn will set about 30 minutes earlier each night. Saturn sets at 4:13 a.m. Saturn will reach superior conjunction on February 4, 2022.

James S. McDonnell Planetarium

Night Sky Update: August 27-September 4, 2021