This is the Saint Louis Science Center’s DAY SKY UPDATE for the Month of October 2025.
Information updated monthly 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. Additionally, times will be posted in a 24-hour format.
Join us for our next solar telescope viewing, Sunday, October 19, held in association with the St. Louis Astronomical Society. These viewing sessions are weather dependent.
For details, see the information at the bottom of this page or visit: https://www.slsc.org/explore/mcdonnell-planetarium/public-telescope-viewings
Daytime Astronomy Primer
For most, astronomy is a hobby that is left to the darkness of night. While most astronomical objects are only visible at night, the day sky can offer a careful observer several astronomical targets along with a multitude of atmospheric phenomena to enjoy. When posted, the DAY SKY UPDATE will explore these possibilities which may include a highlight of the month, cloud observing, sun rise/set times, daytime Moon information, daytime planets and other topics. As always, when viewing during daytime, you must use caution as the Sun is always near.
Aside from solar filters, there are other safety steps that you should consider. Sunscreen, hats and sunglasses are always advisable. Visible light is how we observe the world around us, however, there is light we cannot see. Ultraviolet (UV) and infrared (IR) light are great examples of this. While both are an issue if you are using an optical system, UV light is an issue through exposure. This can be mitigated by using sunscreen, sunglasses and limiting exposed skin. While sunglasses are not safe instruments to view the Sun with, they do protect your eyes from exposure to ultraviolet light that we are susceptible to during the day. If you would like to learn more about UV and its dangers use the buttons below.
Cloud of the Month
With the coming of fall bringing apple cider donuts, hayrides, and dusting off the crockpot, it also means the changing of the leaves, cooler temperatures, and a transition from supercells to steady rain showers. The clouds that provide us with the prolonged steady precipitation we think of during the changing of seasons are known as nimbostratus clouds.
There are only two types of clouds that produce precipitation, cumulonimbus and nimbostratus, and the way they form is very different. All cloud formation starts with a moist atmosphere that provides water vapor, something for that water vapor to condense onto like dust, pollen, sea salt (these are known as condensation nuclei), and for saturation to occur by warm air rising, expanding, and cooling.
Cumulonimbus clouds form vertically, so they can get very tall, in some cases even reaching the tropopause. Instability is the key factor here; unstable air is going to be warmer than the surrounding air and it will want to continue rising. For cumulonimbus clouds, the mechanism that mostly triggers this unstable air to continue rising is convection, an atmospheric vertical motion due to surface heating. The sun heats up the ground, which in turn warms the air above it, making the air less dense and start to rise. Cumulonimbus clouds are also associated with severe weather and random downpours.
Nimbostratus clouds on the other hand are formed a little different. Instead of relying on convention to get air parcels to rise, they form from advection, the horizontal transfer of air. This will normally come from warm fronts or occluded fronts (when a cold front catches up to a warm front). Because warm air is less dense than colder air, the warm air mass will slowly rise above the colder air mass. The warmer air will continue to rise, expand, cool, and condense to form the nimbostratus cloud deck. Nimbostratus clouds will provide steady continuous precipitation, and the intensity will usually be light to moderate. Depending on the frontal system, precipitation can last for several hours to several days. You will never deal with hail, lightning, or thunder during these showers. If you do, then it is coming from a cumulonimbus cloud.
Nimbostratus clouds are widespread low-level clouds that are dark grey in appearance. One of the main distinctions between nimbostratus and altostratus is the fact that you cannot see the sun or moon through the layers of nimbostratus. Another feature one might notice are these ragged disconnected fragments of clouds that will form beneath the nimbostratus clouds known as scud. They form when rain evaporates and mixes with the air right below the cloud deck and the air will then saturate, creating these irregular looking clouds. Scud clouds will normally appear darker and look kind of wispy as well.
It’s also important to mention that rain is not the only precipitation produced from nimbostratus clouds. Snow, sleet, and freezing rain may also form which in turn can also be persistent and steady.
When one thinks of autumn, those gloomy steady rainy days might come to mind. And now you know what makes them different from the pop-up storms we tend to see in the springtime. Remember that nimbostratus clouds bring continuous precipitation, whether it’s rain or snow.
The Sun and the Moon
Sun Information
The month of October sees the Sun continue towards its southern standstill. If you track the position of sunrise or sunset this month you will find these positions are shifting to the south. Maximum altitude also changes each day. The Sun’s maximum altitude will shift from 47.9° on October 1, 2025, to 37.0° on October 31, 2025.
The next major position of the Sun occurs on December 21, 2025, as the Sun reaches the December solstice. For us in the northern hemisphere, this is the winter solstice which signals the start of winter. Be on the lookout for Orb Weaver spiders are active, leaves are starting to fall and some areas in Missouri expected to experience their first frost of the season.
Sunrise and Sunset Times for St. Louis Missouri
The sunrise and sunset times below were calculated by the Earth Systems Research Laboratories for NOAA. These times are calculated using equations for Jean Meeus’s Astronomical Algorithms. The atmosphere complicates these calculations due to the refraction of sunlight as it passes through the atmosphere. For the times listed below, the amount of atmospheric refraction is assumed to be 0.833°. Variations in the atmosphere can change the amount of refraction so the times posted are accurate to within a minute for latitudes between +/- 72°. You can learn more about these calculations and where to generate times for areas outside of St. Louis, Missouri by using the buttons below
Moon (daytime views)
Last quarter moon occurs on October 13, 2025, and first quarter moon occurs on October 29, 2025. The best daytime views of the Moon are always near the quarter phases. Look for the Moon in the morning at the beginning of October. When we are near first quarter phase, look for the Moon in the afternoon. The Moon crosses the ecliptic at its ascending node this month on October 5, 2025, and then at its descending node on October 18, 2025. This behavior occurs because the Moon’s orbit around Earth is tilted about 5.1° with respect to Earth’s ecliptic. This nodal cycle of the Moon is called a draconic month which 27.2 days long. Being aware of these crossing nodes helps observers know if the Moon will appear south or north of the ecliptic.
Solar Sunday is now held every 3rd Sunday of the month from 11:00 a.m. until 3:00 p.m. (Weather Dependent)
On the third Sunday each month, the St. Louis Astronomical Society and the Saint Louis Science Center will set up a number of safe solar telescopes outdoors and be on-hand to answer your questions. Telescope viewing begins at 11:00 a.m.
The St. Louis Astronomical Society helps host the monthly Star Parties at the Saint Louis Science Center. In addition to our daytime viewings, they also help facilitate our nighttime Public Telescope Viewing. These nighttime viewing sessions occur on the 1st Friday each month. Visit SLAS’s website linked above to learn about other telescope events SLAS hosts around the St. Louis area.
The Day Sky Update is compiled by McDonnell Planetarium staff.
