The sizzling summer heat may not seem like it's ready to give way to cooler, crisper fall air any time soon, but autumn will be here soon no matter what the weather forecast has to say about it.

Meteorological fall begins Sept. 1, and astronomical fall begins with the autumnal equinox at 7:43 a.m. Sept. 22. Astronomical seasons are based on Earth's position in relation to the sun, with spring and fall each beginning with an equinox and summer and winter starting with a solstice, according to the National Oceanic Atmospheric Administration. The dates of these equinoxes and solstices are not always exactly the same, sometimes varying slightly from year to year.

Meteorological seasons, on the other hand, begin on the same date year after year: spring on March 1, summer on June 1, fall on Sept. 1 and winter on Dec. 1. These groupings of months are based on the temperature cycle and also more closely align with the calendar than astronomical seasons, NOAA reports. Classifying the seasons like this makes it easier to track weather cycles and trends and even weather records because the seasons always fall on the same dates from year to year.

Like other seasons, fall brings with it recognizable changes — some welcome, other not so much. We will see the change of seasons in our local wildlife. Some animals will disappear, either to migration or hibernation, while others will be scurrying around in preparation for winter. The leaves will change color and then drop, and other plants will start to die back too. And along with cooler temperatures, the sun will continue to set earlier and earlier each day.

Those earlier sunsets aren't welcome by many of us, but they do give us more time for gazing up at the night sky, and there will be a few things to keep an eye out for in September. If planets are your thing, early September provides a few good viewing opportunities. On Sept. 5, Mercury will be at its greatest western elongation, and on Sept. 8, Saturn will be at opposition.

The best time to see Mercury is when it is at its greatest eastern or western elongations. On Sept. 5, when it is at its greatest western elongation, you'll be able to see our planetary neighbor in the eastern sky just before the sun rises. A few days later you can get a good look at Saturn when it is at its closest position to Earth and well illuminated by the sun. On Sept. 8, you'll be able to see Saturn unaided in the night sky, but with the medium or large telescope you will see its rings and even some of its moons SeaSky.org reports. 

As the month progresses, keep an eye out for news about a comet called A3 Tsuchinshan-ATLAS. Sky scientists have been monitoring this planet since it was spotted in early 2023, and it is expected to become more easily visible in September and into October as its orbit brings it close to both Earth and the sun for the first time in 80,000 years, National Geographic reports. There's some uncertainty about how visible it will be in the sky, but it may even be visible with the naked eye. 

September's full moon is usually called the harvest moon, and it will be on Sept. 17 this year. It will reach its fullest point at 9:34 p.m. The harvest moon is the full moon that occurs nearest to the autumnal equinox, so while it is usually in September it can also occur in October, according to the Old Farmer's Almanac. When the harvest moon is in October, the September full moon is called the corn moon.

The September full moon will also be the second of four consecutive supermoons. A supermoon occurs when the full moon is at the same time that the moon is at its closest approach to Earth, making it look 14% to 30% larger than the faintest moons of the year, called micromoons, according to NASA. Micromoons occur when the moon is at its farthest point from earth during the full moon.  

September's harvest supermoon — or would you call it a super harvest moon? — will also undergo a partial lunar eclipse, giving you one more reason to mark your calendar for the night of Sept. 17. A partial lunar eclipse occurs when part of the moon enters Earth's shadow during a full moon, making it look like part of the moon is missing, according to Space.com.

The Sept. 17 lunar eclipse will be visible across much of North America, including Illinois, as well as South America and parts of Africa, Antarctica, Asia and Europe. It will begin at 7:41 p.m. and reach its fullest point — when the largest part of the moon will appear missing — at 9:44 p.m. The eclipse will end at 11:47 p.m.

The super harvest moon partial lunar eclipse isn't the end of the fun for sky watchers in September. Two meteor showers kick off at the end of the month, with the southern Taurids beginning Sept. 23 and the Orionids getting underway a few days later on Sept. 26. 

The southern Taurids is a long meteor shower, running from Sept. 23 to Dec. 8, but it doesn't usually produce more than a handful of meteors per hour, even at its peak, which will be the night of Nov. 4 to 5, the American Meteor Society reports. The better viewing opportunity comes with the Orionids, but it, too, isn't as big a producer as showers like the Perseids.

The Orionids generally produces 10 to 20 meteors an hour, but some years it far exceeds that, producing as many as 50 to 75 meteors an hour, the meteor society reports. This year, the Orionids will peak the night of Oct. 20 to 21, but viewing will be limited because the moon will be 83% full that night.