The First Night of Autumn
The Autumnal Equinox is upon us! Look up for some wonderful fall stargazing. Here’s viewing information and our complimentary, printable September Sky Map to help you navigate easily.
Just click here or on the image below to open the printable map—then bring outside!
The Autumnal Equinox
Autumn officially begins on Monday, September 23. For astronomers, it’s the Autumnal Equinox, when the Sun crosses the celestial equator. For the rest of us, this marks the date when the hours of daylight and darkness are approximately equal.
It’s all downhill after that! The days grow even shorter and the nights get even longer for the next 3 months, until late December, when the trend reverses and the nights at last begin to shorten. Read more about the Autumnal Equinox here.
September is a terrific time to go stargazing. In the Northern Hemisphere, the worst of the summer heat is gone. It’s the sort of weather that encourages you to linger under the stars and wander through the sky.
Autumn’s Many Asterisms
Looking east-southeast on Equinox Night—September 23—you won’t see many bright stars. Nevertheless, there’ll be plenty of distinctive asterisms (unofficial star patterns), including the prominent Great Square of Pegasus, the Winged Horse. The Great Square encloses an area of sky with few stars visible to the unaided eye, making its interior look nearly empty. Pegasus is upside down from our point of view, but you can easily trace his graceful neck and head, which ends with the star Enif (“the Nose” in Arabic). The front legs of the Winged Horse are also easy to spot.
Just off The Nose is a small pattern of four stars representing Equuleus, the Foal, a close relative of Pegasus. Above Equuleus is another tiny constellation, Delphinus, the Dolphin. Despite making up one of the smallest constellations, the five stars of Delphinus have been recognized as a leaping dolphin for thousands of years.
Below the Great Square lies the constellation Pisces, representing a pair of fish bound together at their tails. The five-sided Circlet asterism comprises the head of the right-hand fish, and The Vee marks the spot where the two fish are joined. The star Alrescha (“the Cord”) connects the fishy pair forever.
A third fish swims nearby in the form of Piscis Austrinus, the Southern Fish. The only bright star on this month’s map is found in Piscis Austrinus. It’s Fomalhaut, an Arabic word that translates as “the mouth of the fish.”
To the left of the Great Square, you’ll find the big W shape of Cassiopeia, the Queen. In mythology, Cassiopeia is the wife of Cepheus, the King of Ethiopia, part of whom can be seen at the top of our map.
Finally, the lower left of our map holds a stargazing challenge, if you’re up to it, in the constellation Perseus, the Hero, who once rescued Andromeda from a sea monster.
For our purposes, Perseus is home to a most amazing star, Algol, the Demon Star. Most of the time, Algol is a little dimmer than the nearby star Mirfak. But every 2.86 days, Algol dims dramatically, so much so that you can easily notice as it becomes fainter.
Here are some opportunities to see Algol at its dimmest this month (all are Eastern Time):
- September 4 @ 05:17 A.M.
- September 7 @ 02:05 A.M.
- September 9 @ 10:54 P.M.
- September 27 @ 03:46 A.M.
- September 30 @ 00:34 A.M.
The dimming and re-brightening takes several hours, so find Algol 2 to 3 hours before the listed times and compare its brightness to that of nearby stars. Then return at the time of minimum brightness and note how much Algol has dimmed. It’s quite extraordinary!
September 2019 Sky Map
Click here or on map below to enlarge (PDF).
Sky map produced using Chris Marriott’s Skymap Pro
Note: How to Read the Sky Map
Our sky map does not show the entire sky which would be almost impossible. Instead, the monthly map focuses on a particular region of the sky where something interesting is happening that month. The legend on the map always tells you which direction you should facing, based on midnight viewing. For example, if the map legend says “Looking Southeast,” you should face southeast when using the map.
The map is accurate for any location at a so-called “mid northern” latitude. That includes anywhere in the 48 U.S. states, southern Canada, central and southern Europe, central Asia, and Japan. If you are located substantially north of these areas, objects on our map will appear lower in your sky, and some objects near the horizon will not be visible at all. If you are substantially south of these areas, everything on our map will appear higher in your sky.
The items labeled in green on the sky map are known as asterisms. These are distinctive star patterns that lie within constellations. When getting your bearings under the stars, it’s often easiest to spot an asterism and use it as a guide to finding the parent constellation.
The numbers along the white “Your Horizon” curve at the bottom of the map are compass points, shown on degrees. As you turn your head from side to side, you will be looking in the compass direction indicated by those numbers. The horizon line is curved in order to preserve the geometry of objects in the sky. If we made the horizon line straight, the geometry of objects in the sky would be distorted.