Chicago’s Adler Planetarium Offers Special Programming and Viewing Tips for October’s Arrival of Comet C/2023 A3

Get ready to look up to stars to see something unique. In October 2024, Comet C/2023 A3 (Purple Mountain-ATLAS) will be making its closest approach to the Earth after traveling for tens of thousands of years from the fringes of our solar system.

In honor of this historic event, Chicago’s Adler Planetarium, as part of its “Adler at Night” program, is offering free general admission to the Adler Planetarium for Illinois residents (with proof of residency) every Wednesday evening from 4:00 pm–10:00 pm.

During “Adler at Night” events on October 16, 2024, and October 23, 2024, the Adler Planetarium will offer free binocular and small telescope viewing of the comet on the west side of the Adler’s main building. Depending on local weather conditions, the comet’s brightness, skyline obstructions, and the effects of light pollution, the tentative comet viewing schedule will be on October 16, 2024 (6:45 p.m. – 8:00 p.m. CT) and on October 23, 2024 (6:45 p.m. – 9:00 p.m. CT).  Note that due to the comet’s location in the sky to the west, the Adler’s Doane Observatory, which is located east of the Adler Planetarium main building, will not be used to view the comet. 

In addition, starting at 6:00 pm CT on Tuesday, October 15, 2024, the Adler Planetarium will host, “Comet C/2023 A3 Live!”, a special edition of its popular YouTube program, Sky Observers Hangout, to help viewers find the comet in the sky for themselves. 

In anticipation of the comet’s arrival, the Planetarium has offered some recommendations for witnessing this rare spectacle.  Observers should note that on October 9, 2024, right at the time of sunset, the low angle between the comet & the Sun means that sunlight scattered by dust from the comet might temporarily bump up the comet’s brightness to around magnitude -2.5, which is about as bright as Jupiter is in our night sky. However, it will still be very difficult to see while looking through so much air and with so much sunset glare. It will also be above the horizon for only about 15 minutes after sunset before the comet itself sets. The comet could be nearly as bright just after sunset on October 10-11, 2024, & slightly higher in the sky. 

On October 12, 2024, the comet will be at its closest point to Earth, just under 44 million miles away. On October 12-13, 2024, the comet’s brightness will be around magnitude +2.5, or about as bright as Polaris, the North Star. It will begin to dim rapidly after that date. By the end of October 2024, the comet will likely be at around magnitude +6, which is at the human limit of naked-eye visibility under a very dark sky. Viewers in light-polluted locations will probably need binoculars or a small telescope to see the comet during the last half of October. The last comet of similar brightness seen in our area was comet C/2020 F3 (NEOWISE), which made its closest approach to Earth on July 22, 2020, and peaked at magnitude +1.

While there is no one specific “best” place to go to view the comet, it may be seen anywhere with a very clear view to the west and southwest sky, especially locations with sightlines all the way down to the west and southwest horizon. Viewing locations without horizon obstructions such as buildings or trees will be preferable. Viewers in locations that are far from city lights and well away from light pollution will be better placed to find the comet.

The comet will look like a small, fuzzy glowing cloud. A pair of binoculars may show a bit of the comet’s tail pointing up & away from the Sun. Wait until the Sun fully sets to try finding the comet using your eyes or binoculars.

The Adler Planetarium would like to remind everyone that tickets to the “Alder at Night” programs must be reserved online, in advance, at tickets.adlerplanetarium.org. For additional information on the Alder’s comet viewing schedule, please follow the Scopes with the Adler on Facebook.