Happy equinox!

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Sunday is the Autumnal Equinox, where day and night are the same length (except for a few minutes on either side caused by such trivialities as the ellipticity of the Earth’s orbit and refraction due to the atmosphere, which makes daylight last longer).

On September 23 at 09:51 UT (5:51 a.m. Eastern US time) the Sun’s position in the sky is exactly halfway between its farthest excursion north in the summer and the farthest south in winter (if you are in the southern hemisphere, swap the seasons). That’s the actual definition of the equinox; it’s an astronomical event that is only mildly connected to the seasons.

You can also try standing an egg on end if you like… but make sure you try it again in a week.

Here in Boulder, you’d hardly notice. It was hot all week, and still pretty toasty as I write this. The mountains, kilometers away, are almost totally devoid of snow. I imagine in a month that scene will change, and in two months things will look a lot different. Snow again! Woohoo!

Of course, by December 22 — the Winter Solstice — we’ll see how happy I am about cold weather.

September 22nd, 2007 5:42 PM by Phil Plait in Science | 23 comments | RSS feed | Trackback >

23 Responses to “Happy equinox!”

  1. 1.   rich (richmanwisco) Says:

    Oh wait! Hold on while I get my egg!

  2. 2.   Seamyst Says:

    I just wish it’d rain, the grass here is all parched and brown.

  3. 3.   Jim Downey Says:

    You know, if you stand an egg on end that is smeared with the blood of a horse right at the moment of local noon, then the anti-Christ will be revealed in the shadow (but only if you sprinkle your glasses with holy water from Atlantis).

    It is said that the image resembles George W. Bush.

    Jim D.

  4. 4.   Quiet Desperation Says:

    I’m in Southern Cal. I think we got your rain.

    Although we needed it, so thanks. :)

  5. 5.   Quiet Desperation Says:

    >>> holy water from Atlantis).

    Wait… the destruction of Atlantis predates Christianity!

    Ha! DEBUNKED! :)

  6. 6.   Richard B. Drumm Says:

    Happy equinox back atcha!
    Maybe the Young Astronomer will take up skiing!
    We got almost no snow at all last year here in Charlottesville, your old stomping grounds… :-D
    It was HOT here today as well…
    You should see how McCormick Observatory’s coming along! All new electrics/electronics on the Clark’s mount, a temporary new control paddle, the pier’s control panel -GONE- (well, it’s in the basement, along with everything else) digital encoders are coming…
    Rich

  7. 7.   Evolving Squid Says:
  8. 8.   The Squid Zone Says:

    Happy Autumnal Equinox…

    On 23 September at 0951 UTC, the earth will experience the Autumnal Equinox… more commonly known in North America as The first day of Autumn. It is often rumoured that you can stand eggs on end near the equinox, even…

  9. 9.   tacitus Says:

    Snow? What’s that?

    Greetings from Central Texas :)

  10. 10.   Quiet Desperation Says:

    More eggs on end:

    A big one with *multiple* chicks!
    http://whimsicalwill.tripod.com/CMSI/CMSIChick2.JPG

    Wow. This one is *really* reacting to the equinox!
    http://www.crazyaboutgadgets.com/uploads/oggz1.jpg

    Record holder for the largest egg to bird ratio in the world! Man, that must be some set of labor pains…
    http://www.jschatz.com/eggbirdfeeders/images/wildbirds/071304/PICT4223.jpg

    ZOMG!
    http://www.cedarlodge.yk.net/images/650egg.jpg

    Ack! They are legion!
    http://davidwonn.kontek.net/images/equinox.jpg

    Now they’re organized with leaders! Ten HUT!
    http://www.astrosociety.org/education/publications/tnl/62/images/SM_8EGGS.JPG

    Who’s this guy?
    http://apod.nasa.gov/apod/ap030923.html

  11. 11.   Quiet Desperation Says:

    >>> Snow? What’s that?

    I think it’s something you snort.

    Greetings from Southern California. :)

  12. 12.   Thomas Siefert Says:

    You should try to convince people to stand an egg on it’s end on Shpadoinkle day rather than at equinox, just prove the point.

  13. 13.   Ahruman Says:

    The real question is whether the solstices are the only days when you can lay an egg down flat.

  14. 14.   llewelly Says:

    Given the huge abnormal deficit in Arctic sea ice ( ice extent news or ice area news ) , it is likely that winter will be late and mild over much of the Northern hemisphere.
    I do wonder how much snow you’ll see by December 22nd.

  15. 15.   Encolpius Says:

    This morning I removed a hard-boiled egg from the refrigerator, cracked the shell and peeled it effortlessly, proving that eggs peel effortlessly on the equinox! Explain that, smartypants!

  16. 16.   Kulvinder Matharu Says:

    Hey, it’s “Happy Autumn Equinox”! LOL

    September here in London has also been warm and sunny, which contrasts with the quite wet and miserable summer this year. Has enabled me to get out on my mountain bike after a summer of neglect.

    I guess summer isn’t over until we switch our clocks from BST to GMT at the end of next month. Or does summer end today? This will cause endless debate at the office tomorrow I think!

  17. 17.   Chris Says:

    Well – the Forecast for the Denver/Boulder area says the fist day of Fall will actually be very fall-like. A decently strong cold front coming through will see to that. This is still my favorite time of year here – driving the Peak to Peak Highway from Nederland to Estes Park and watching the Aspen turning is something not to be missed!

    Of course, if you grew up in Boulder on “The Hill” like I did, you’d understand that we actually have 4 seasons in Colorado: Almost Winter, Winter, Still Winter, and Construction…

  18. 18.   Edward Cohen Says:

    Tacitus, I was stationed in Texas (Camp Hood) in 1949, and early 1950.
    There was snow and ice that season. My parents came to pick me up
    in January and their hubcaps were covered with ice. First snow/ice in
    years.

  19. 19.   Steve Says:

    “… the Sun’s position in the sky is exactly halfway between its farthest excursion north in the summer and the farthest south in winter…”

    To me, that seems practically the same as saying, when the Sun is over the equator. I.e., when the latitude is zero.

    I thought the USNO’s definition of the equinox was when the Sun was at apparent ecliptic longitude of 180 degrees. I wonder what the time difference has been over the centuries?

  20. 20.   John Money Says:

    Down here in South Florida it hasn’t stopped raining for 5 days. You can have some of it if you wish!

    John

  21. 21.   Mena Says:

    It’s supposed to be 91F/33C in the Chicago area tomorrow (9/24). I would do my usual “MAKE IT STOP!!!” but it looks like it may actually be the end of this heat wave. The plants may really have to come in…

  22. 22.   Chris Gegere "G-gear" Says:

    Concerning:
    Tides, the Earth, the Moon, and why our days are getting longer
    http://www.badastronomy.com/bad/misc/tides.html

    Phil (& Co.),
    Please read this following excerpt from your article:

    “Despite all this confusion, the Earth’s rotation is in fact slowing down. Eventually, the Earth’s rotation will slow down so much that the bulge will line up exactly between the centers of the Earth and the Moon. When this happens, the Moon will no longer be pulling the bulge back, and the Earth’s spin will stop slowing. But when this happens, the time it takes for the Earth to rotate once will be slowed to exactly the same time it takes for the Moon to go around the Earth once! If you were to stand on the Moon and look at the Earth, you would always see the same face of the Earth.”

    Phil’s scientific and predictive explanation raises some questions:

    Why hasn’t this already happened?
    (If the solar system is billions of years old?)

    Maybe, the solar system, let alone universe, isn’t that old!

    Chris

    cgegere@tctwest.net

  23. 23.   Buzz Parsec Says:

    Chris -

    The slowing of the Earth’s rotation is an ongoing process. It has been going on for billions of years and will continue for billions more. But “billions of years” isn’t forever. It will eventually happen. I don’t know the exact number but it has been calculated, and observed. IIRC, it will take about 2 billion more years, so we are about 2/3rds of the way through the process. The Sun will run out of fuel (Hydrogen) in about 5 billion years, so the Earth-Moon system will become tidally locked long before that happens.

    There are at least 2 direct physical observations that directly support this. I think there are ancient sedimentary rocks (100’s of million years old) that show there were more days in a year than there are now (i.e. the Earth rotated faster), and direct measurements of the distance to the Moon using the Apollo laser reflectors show that the Moon is receding from the Earth, another consequence of the same theory.

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