Today is the equinox. The autumnal equinox, to be precise. Astronomically-speaking, the equinox is more than just a box marked on a calendar or the start to fall.
Astronomers define the autumnal (fall) equinox as the moment when the Sun crosses the Celestial Equator, heading from the north to the south. And what is the Celestial Equator? It’s just the projection of the Earth’s equator onto the heavens. As the Earth rotates, the Celestial Equator appears as the 
midpoint of the sky’s motion.
midpoint of the sky’s motion.The Sun doesn’t always stay on the Celestial Equator – if it did, the Earth would be a very different place. Because the Earth is tilted with respect to its rotation (see the image to the right), the Sun actually appears to move north and south throughout the year. The Sun is to the north of the Celestial Equator during the summer, and to the south of the Celestial Equator in the winter. Without the tilt causing this motion, we wouldn’t have any seasons at all!
As the Earth revolves around the Sun throughout the year, there are two points when the Sun appears to cross the Celestial Equator. These are the equinoxes. Six months from each other on the calendar, the vernal (spring) and autumnal equinoxes mark the moment when the Sun crosses the Celestial Equator heading north and south, respectively. This year, the autumnal equinox happens at exactly 5:19 PM in New York City.
What does all of this mean for an observer on Earth? First of all, on the equinox, the day and night are of equal length. 12 hours of sunshine (or clouds, if you’re unlucky) and 12 hours of darkness. But this is just for one day. As we travel through the fall and head toward winter, the days will shrink, while the nights grow. You probably won’t notice the difference from day to day – it’s only a couple of minutes at most.
You will, however, see a difference after a couple of months. The days will continue to shorten until the winter solstice in December. On that day, we will only see 9 hours and 16 minutes of daylight in New York City. So take advantage of that daylight while we still have it!
Comments
This is very cool i woundnt have ever known this until my history teacher called and told my mom what i hada look up!
omg this stuff is heakah intristing!!
"Starting tomorrow, the days will shrink, while the nights grow"
This actually happens on the day after the summer soltice ie the first day of summer, which is the longest 'day' of the year (shortest night). And depending what time you rise, the effect has been quite noticably darker recently.
For the more science minded, the equinox represents the biggest single-day change in the length of day or night, and the lenghening of the night starts to slow Starting tomorrow, relatively speaking.
(If you are in calculus class, the first derivative of the length of the day is maximized on the equinoi/equinoxes).
today is fall equinox and my baby turns 5months today at 2:29pm
Thiis Iis Soo Awsomee Ii Nevver Kneww Nothhinqq Aboutt Thiis Till Noww
The Sun be northward during summer in the Northern Hemisphere, you mean....
Actually, the day and night are not always of equal length on the equinox. Today, sunrise (Eugene, Oregon) was at 7:00 am, and sunset today will be 7:09 pm. Close, but not equal. On Saturday the 25th, the sunrise will be at 7:03 am, and the sunset at 7:04 pm, which will be the closest it gets this year to equal day and night.
hi
sep 22 is very intresting my science techer told me today about equinox coolio
otem sux boooooo!!!!!!!!!!!!!!!!!! and go winter
As someone pointed out, the days and nights are NOT exactly equal on the equinox. Thanks to our atmosphere and the size of the Sun in the sky, we actually get a little more than 12 hours of sunlight today. If there were no atmosphere to bend the Sun's light and if the Sun were a point instead of a disc, then and only then would the day and night be exactly equal on the equinox.
YAY!! Summer's over, I can now go outside to play and not die in 90+ degree heat :)
a lot of people hate the fact the days are shorter, but the cooler weather is like Spring to me haha!
YAY!! Summer's over, I can now go outside to play and not die in 90+ degree heat :)
a lot of people hate the fact the days are shorter, but the cooler weather is like Spring to me haha!
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