Night Sky Update: November 25-December 3, 2023 - Saint Louis Science Center (2024)

This is the Saint Louis Science Center’s NIGHT SKY UPDATE for the week of Saturday, November 25, 2023.

Information updated weekly or as needed.

Times given as local St. Louis time which is Central Standard Time (CST). 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 -6 hours when CST.

Observing Highlight of the Week

Circumzenithal Arc seen from St. Louis Missouri on November 25, 2023. Displays like this are caused by light passing through ice crystals at high altitudes in our atmosphere. Image credit: Eric Gustafson.

As winter approaches, now is a great time to start looking for atmospheric optics. These beautiful displays are visible both day and night, they require no special equipment, and anyone can learn to spot them. If you have ever found yourself watching the clouds go by and noticed a rainbow after a storm, or a circle of light around the Sun, then you have seen one of the many types of atmospheric optics that are possible.

Atmospheric optics are displays caused by light interacting with our atmosphere. Drops of water, ice crystals or particulates in the atmosphere can interfere with light before it reaches our eyes. Every bit of light passing through our atmosphere will be distorted in some way. The Sun and Moon may be the primary objects connected to the optical displays we see, but any light source such as distant stars, planets or human sources can also be the source. A few common examples of how the atmosphere distorts light are the blue color of the day sky, the colors visible at sunset or sunrise, and the apparent twinkling of stars.

While the examples above are familiar sights to most, specific conditions in the atmosphere can lead to several striking displays that often go unnoticed. Rainbows are a good example. Most of us have likely spotted a rainbow after a storm passes by. To see a rainbow, you simply need drops of water in front of you and a light source behind you. Light rays are reflected and refracted by the water as the light passes through it leading to the appearance of a rainbow. There are several orders of rainbows that can be produced. The rainbow orders we commonly see are primary and secondary bows. The different orders are produced based on how many internal reflections occur in the water droplet. Always be on the lookout for a rainbow if a storm has recently passed by and the Sun is below 42° above the horizon.

Another type of optic you may have seen are ice halos. These are displays caused by light passing through ice crystals. The most commonly seen are 22° halos which are visible year-round. These occur as light passes through poorly aligned hexagonal ice crystals. They appear as a circle of light around the light source. They are commonly seen with the Sun but can also be seen around the Moon. There are a multitude of frequent and infrequent halos. The different types are dependent on factors such as solar altitude and the shape and orientation of the ice crystals the light passes through.

Anybody can learn to spot these optics by learning what conditions in the atmosphere produce them. Cloud type, time of year and the Sun’s position in the sky are good factors to start with. Today, while driving into work, I noticed our cloud cover in St. Louis was mostly high-altitude clouds. They were a mix of cirrus and cirrocumulus or cirrostratus clouds that are prone to producing halos. In between star shows in the planetarium, I poked my head outside to see what was there. While the displays were not the best I had seen, I did spot sundogs, a dim 22° halo and a circumzenithal arc (CZA). Sundogs and CZAs require hexagonal plate-like ice crystals to form. CZAs also require the Sun’s altitude to be below 32.3°.

There is no ideal time of year to spot atmospheric optics, however there are some produced during snowy conditions. Those that travel to snowy regions can be treated to spectacular and in some cases rare displays of atmospheric optics. Keep in mind that any light source can cause an optic to be seen but they are most commonly associated with the Sun and Moon. If you plan to look for these in the daytime, always use precaution and do not look directly at the Sun. I will often position myself near a building or lamp post or some other occluding body to obscure the Sun from view. Always remember that the Sun can blind you so take the proper precautions.

This week is a good opportunity to look for optics associated with the Moon. Atmospheric optics are often spotted near the Moon when it is nearing its full phase which occurs on November 27, 2023. If your local weather conditions are ideal, be on the lookout for optics such as ice halos and coronae.

If you would like to learn more about atmospheric optics, there are several resources available online. My go to resources are the two websites produced by atmospheric optics expert Les Cowley. You can find those at

https://atoptics.co.uk/

https://old.atoptics.co.uk/

Atmospheric optics are often associated with the Moon. Above you can see an atmospheric optic caused by water droplets on the left and one cause by ice crystals on the right. Image credit: Eric Gustafson.

The Sun and Moon

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

Sun

Sunrise is at 6:53 a.m. on Saturday, November 25 and sunset is at 4:42 p.m. providing us with less than 10 hours of daylight this week. Even after sunset, light from the Sun will dimly illuminate our sky for about 1 hour and 30 minutes. This period is called twilight, which ends around 6:15 p.m. this week. For those with a sundial, local noon occurs around 11:47 a.m. this week.

Moon

Moonrise for Saturday, November 25 was at 4:30 p.m. and moonset occurred at 6:10 a.m. the following day. On Saturday, November 25, the Moon will exhibit a waxing gibbous phase with roughly 97% disk illumination. By the end of the week the Moon will exhibit a waning gibbous phase with 64% disk illumination. Full moon occurs on November 27, 2023, at 3:16 a.m.

International Space Station (ISS) Observing

There are several visible passes of ISS from St. Louis for the week of November 25. They occur during evening hours. The table below lists the best of these passes that will be seen from St. Louis. If you do not live in the area, you can use https://heavens-above.com/ to set your viewing location and get times for where you are.

Catch ISS from St. Louis starting Saturday, November 25, 2023

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°.

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 southeast at 6:30 p.m. on November 26, 2023. Credit: Stellarium, EG

Looking east at 4:30 a.m. on November 27, 2023. Credit: Stellarium, EG

This week, three naked eye planets will be visible. Saturn and Jupiter are visible once it is dark with Saturn in the south and Jupiter in the east. Venus will be easy to find in the east before sunrise.

Venus

Venus rises this week around 3:18 a.m. It will be easy to spot for most by 4:30 a.m. If you have a clear view of the planet, telescopes will reveal a gibbous phase with roughly 66.2% disk illumination. Now that Venus is past dichotomy, it is beginning to head back towards the Sun from our perspective. As this continues, Venus’s disk illumination will increase as it heads towards superior conjunction on June 4, 2024.

Jupiter

Jupiter has passed opposition and as such it will rise before the Sun sets. Jupiter will be easy to spot in the east once it is dark outside. If you have considerable trees or buildings to the east, you may have to wait about an hour after sunset to spot this giant world. Jupiter will set around 4:39 a.m.

Saturn

Start looking for Saturn in the south about 30 minutes after sunset. If you have lots of trees or buildings, you may have to wait an hour or so after it rises before it will be visible. Saturn will set around 11:09 p.m.

James S. McDonnell Planetarium

Night Sky Update: November 25-December 3, 2023