This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Friday, October 15, 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

22° lunar halo visible due to ice crystal in the cloud cover.
Image credit: Eric Gustafson

The Moon is a favorite target for many observers. Of everything I have shown people through a telescope, nothing gets a reaction like the Moon. Whether it be through telescope, binoculars or just plain old eyes, the Moon always has something to offer us. That said, the Moon can also prove to be problematic. As the Moon nears its full phase, it appears much brighter. Yes, we are seeing more of the Moon reflecting sunlight during gibbous phases, but the main cause of the Moon’s rise in brightness near full moon is the connection between shadow length and Sun angle and eventually the opposition effect. This has a huge impact on those interested in deep sky observing, comet hunters or those hoping to catch a meteor shower.

This week, the Moon will reach its full phase on Oct. 20 at 9:57 a.m. This month’s full moon will unfortunately impact the peak of the Orionid meteor shower. The Orionids peak this year on Oct. 21 in the early morning hours. This meteor shower is a moderate shower that produce about 10-20 meteors per hour at its peak when viewed from a dark location. Meteor showers can vary year to year, and the Orionids have shown increased rates, but that has not happened for several years. It is always worth looking in case this year happens to show an increase, but it is not likely, and a near full moon will be problematic.

So, what can we do when the Moon is bright? For starters, there is no better time to learn about Moon phases. Moon phases are often misunderstood. Frequently, people think the moon phases are caused by Earth’s shadow. The only time the Moon encounters Earth’s shadow is during a lunar eclipse, which only happens during full moon. The next lunar eclipse we will see in St. Louis occurs on November 18/19, 2021. It will be a partial lunar eclipse in which we will see about 97% of the Moon enter the darkest part of Earth’s shadow. Moon phases have long been part of the human experience as it was the main timepiece for many ancient humans. In fact, you and I today still somewhat keep time with the Moon. Our calendar month is still loosely based on the Moon’s synodic cycle. As we approach full moon this week, you will see that the Moon each night will be seen more to the east until full moon on Oct. 20. After full moon, the Moon will rise later each night until it reaches new moon on Nov. 4. Moon phases are caused by the Moon orbiting the Earth. How much of the Moon appears illuminated to us depends on where the Moon is in its orbit.

Bright moonlit nights also change what we look for on the Moon. Fine details on the Moon are always best seen near the terminator. This is the line that separates night and day on the surface of the Moon. There is always a terminator to observe, except during full and new phases. Due to the intense lunar brightness during gibbous phases, it is advisable to use a lunar filter when viewing through a telescope. Because finer details are often lost near full moon, it is a great time to take a tour of lunar maria. These are the large dark patches seen on the Moon with naked eye or in binocular views. Maria are typically caused by two things. First, large scale impacts occurred on the young lunar surface. This created large impact basins that in time would fill with lava, leaving behind the dark material we see. In addition to the dark patches, you will find several brighter areas surrounding a few prominent impact craters. Craters such as Tycho, Copernicus and Kepler are relatively young impact sites. Surrounding them you will see bright rays of ejected material that fell back to the lunar surface. A list of lunar features that are good targets near a full moon can be found here.

Lastly, for those potential cloudy nights ahead, atmospheric optics can often be seen when the Moon is near full. Atmospheric optics occur as light passes through Earth’s atmosphere. Rainbows, sunsets and the twinkle of stars are a few examples. If one is interested in learning about atmospheric optics, the best starting resource can be found at Les Cowley’s website: https://www.atoptics.co.uk/. A common optic to see when the Moon is near full are various types of ice halos. The most common halo to see is a 22° halo. These are caused by light passing through hexagonal shaped ice crystals.

As always, I would encourage anyone to get out and observe whenever they have time. A near full moon or worse yet, cloud cover can put a damper stargazing, but these factors can still provide us with something new to see. Don’t forget October 16, 2021, is International Observe the Moon Night. You can join thousands of people around the world as they celebrate the Moon. Learn more about this annual celebration at https://moon.nasa.gov/observe-the-moon-night/.

The Sun and Moon


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

Sunrise is at 7:10 a.m. on Friday, October 15 and sunset is at 6:22 p.m. providing us with a bit over 11 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 7:51 p.m. this week. For those with a sundial, local noon occurs around 12:46 p.m. this week.

DaySunriseSunset
2021-10-157:10 a.m.6:22 p.m.
2021-10-16 7:11 a.m.6:21 p.m.
2021-10-17 7:12 a.m.6:19 p.m.
2021-10-18 7:13 a.m.6:18 p.m.
2021-10-197:14 a.m.6:16 p.m.
2021-10-20 7:15 a.m.6:15 p.m.
2021-10-21 7:16 a.m.6:14 p.m.
2021-10-22 7:17 a.m.6:12 p.m.
2021-10-23 7:18 a.m.6:11 p.m.

Moon 

Moonrise for Friday, October 15 occurred at 4:26 p.m. and moonset will occur at 2:58 a.m. on the following day. On Friday, October 15 the Moon will exhibit a waxing gibbous phase with about 79% of the lunar disk illuminated. Full moon occurs on October 20 at 9:57 a.m.

International Space Station (ISS) Observing

Credit: NASA

Visible passes of ISS from St. Louis for the week of October 15 occur during morning hours. The best pass this week occurs on the morning of October 22. Use the table below for information about this and other visible passes this week.

Catch ISS from St. Louis starting Friday, October 15

Date Starts  Max. altitude  Ends  
TimeAlt.Az.TimeAlt.Az.TimeAlt.Az.
20 Oct-1.1 06:09:0310S 06:11:3620SE 06:14:1010E
22 Oct-3.5 06:10:4913SW 06:13:4567SE 06:17:0610NE
23 Oct-2.5 05:26:1936SSE 05:26:3436SE 05:29:4210ENE

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 6:45 p.m. October 15, 2021. Credit: Stellarium, EG 

Looking east, at 6:45 am, October 23, 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 after sunset. Mercury will become visible in the east before sunrise by the end of the week.

Mercury

Mercury is starting another morning apparition. This means we are slowly seeing the elusive planet climb out of the Sun’s glare. You can start looking for Mercury in the east about 30 minutes before sunrise. Most of us will have a hard time find Mercury until October 23, 2021, when it will be seen about 10° above the eastern horizon around 6:45 a.m. Mercury reaches greatest western elongation on October 25, 2021.

Venus

Venus is well into another evening apparition. By 6:45 p.m., Venus will be about 14° above the western horizon. Venus will set at 8:22 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.

Mars

The red planet has not been visible for several weeks now. The previous apparition of Mars has ended. But for those itching to see Mars again, you are in luck as the next apparition of Mars begins in November 2021. This week on October 8, 2021, Mars will be in conjunction with the Sun. Slowly after this date, Mars will climb out of the Sun’s glare eventually becoming visible just before sunrise. The next Mars apparition is expected to begin around November 14, 2021, when Mars will appear far enough from the Sun for safe viewing.

Jupiter

Jupiter has passed opposition and as such will be visible about 30 minutes after sunset. Look for Jupiter in the south as it starts to darken outside. Jupiter sets at 2:10 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 south after sunset, but as we continue through the year, Saturn will set about 30 minutes earlier each night. Saturn sets at 12:53 a.m. Saturn will reach superior conjunction on February 4, 2022.

Uranus

Uranus will reach opposition on November 5, 2021, at 0 hrs. UT. For us in St. Louis, that translates to 19:00 or 7:00 p.m. CDT. When near opposition, Uranus can be seen naked eye under dark skies. In St. Louis you will need binoculars to spot this ice giant. Uranus rises at 7:15 p.m. and will be easily found by 9:00 pm in the east in the constellation Aries.

James S. McDonnell Planetarium

Night Sky Update: October 15 – October 23, 2021