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Equinox vs. Solstice

Today is the autumnal equinox – night and day are of almost exactly equal length, twelve hours each. Each year there are two equinoxes and two solstices. Both signify a change of season, but they are very different phenomena.

The biggest difference between the equinox and the solstice is that an equinox is the point during the Earth’s orbit around the sun at which the sun is at its closest distance from the equator, while during a solstice, it’s at its greatest distance from the equator.

In September and March during the equinoxes, all areas of the Earth’s surface receive the same amount of sunlight. The September equinox marks the moment the Sun crosses the celestial equator – the imaginary line in the sky above the Earth’s equator – from north to south and vice versa in March. (Equinoxes are opposite on either side of the equator, so the autumnal (fall) equinox in the Northern Hemisphere is the spring (vernal) equinox in the Southern Hemisphere and vice versa.)

Solstice occurs when the sun reaches its northern or southernmost point (in June and December) — when its path is farthest from the equator. In the Northern Hemisphere the summer solstice happens in June, and in the Southern Hemisphere, the solstice happens in December (this is why the seasons are reversed in each hemisphere). So the winter solstice is the shortest day of the year while the summer solstice is the longest day of the year.

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13 responses

  1. Perry Ellis

    Here’s another way of thinking about equinoxes: focus on what’s going on at the poles instead of what’s going on at the equator. At the moment of exact equinox (3:50 AM Eastern time, Sept. 23, 2019) an observer at the North Pole would see the sun the same distance above the horizon as an observer at the South Pole. The distances would be equal during the equinox (a memnomic that practically writes itself!).

    September 23, 2019 at 9:17 am

  2. Ray Mainer

    It ain’t necessarily so. The difference in distance from the sun between the equator and the Tropics of Cancer or Capricorn is at best a few thousand miles. Not much of a difference considering the sun is 93 million miles from the earth. Both the equator and the Tropics of Cancer and Capricorn are farthest from the sun during the aphelion (about 94.5 million miles) and closest to the sun during the perihelion (about 91.4 million miles). The equinox and the solstice have nothing to do with it. It is cold in the winter because of the sun’s low angle in the sky and the short hours of day light.

    September 23, 2019 at 9:27 am

  3. As I recall there is another “curiosity” that is not mentioned here. Here in the Northern Hemisphere, we are actually closer to the sun in winter than we are in the summertime. It is colder in winter not due to distance from the sun, but due to the angle of the sunbeam to the northern hemisphere.

    September 23, 2019 at 9:43 am

  4. I think you two are actually talking about different things: on the one hand, angle of the sun above the horizon, and on the other hand, actual distance between the earth and the sun?

    I was an elementary school teacher, and I once walked through a colleague’s classroom as he was telling his class that in summer, the earth is closer to the sun, and in winter it’s further away. I didn’t usually interrupt someone else’s lessons, but I couldn’t let that one stand, so I said something like, “You know, I used to think that was why it was cold in winter – that the sun was further away – but then I found out that our part of the world is actually CLOSER to the sun in the winter! How can that be? We know it’s way colder here in winter, and the reason is that the earth’s axis is tilted…” and I grabbed a globe and demonstrated the way the orientation shifts as the earth revolves around the sun, and tried, at least, to show the idea of the low angle of the sun in winter, and the more direct sunlight in summer. I don’t know how much of that the fourth graders understood, but my colleague actually thanked me later!

    September 23, 2019 at 9:45 am

    • Thank you so much for clarifying this, Dell. I was in a bit over my head with this post!

      September 23, 2019 at 11:06 am

    • Bill On The Hill

      I like your version the best Dell… Keeping it simple for dummies like myself!
      Bill… :~)

      September 24, 2019 at 7:31 am

      • Thanks, Bill! I do pretty well at thinking like a fourth grader! : )

        September 24, 2019 at 8:38 am

  5. Alice

    Oh, well: it’s officially Fall! We’ve had some beautiful weather, 87° right now, south of Boston. Enjoy!

    September 23, 2019 at 1:06 pm

  6. Martha Cochran

    Hi Mary. I LOVE your blog!

    I only have one comment about today’s discussion of the equinox v. solstice. You didn’t mention that the sun is actually closest to earth every January, and farthest from earth in July. What you should have said is that during the equinoxes the sun is directly overhead at noon at the equator. But the difference between where the sun is in March and September (i.e. overhead at the tropic of cancer and/or capricorn) v. during the solstices is dwarfed by how much farther away the sun is from earth in summer.

    Martha

    On Mon, Sep 23, 2019 at 8:22 AM Naturally Curious with Mary Holland wrote:

    > Mary Holland posted: “Today is the autumnal equinox – night and day are of > almost exactly equal length, twelve hours each. Each year there are two > equinoxes and two solstices. Both signify a change of season, but they are > very different phenomena. The biggest difference bet” >

    September 23, 2019 at 1:53 pm

    • Thanks, Martha! There’s a reason I don’t do many celestial posts — I am at the very edge of my knowledge and appreciate the valuable information you’ve offered everyone!

      September 23, 2019 at 2:51 pm

  7. Susan

    As always, Mary encourages us to observe our surroundings and learn from that. The discussions that follow are enlightening, entertaining, and engaging. They feed my naturally curious spirit. Thank you all.

    September 23, 2019 at 2:12 pm

  8. Steve Harris

    re: the distance from the sun discussion, there is an excellent summary at: https://www.timeanddate.com/astronomy/perihelion-aphelion-solstice.html (this is a great site, worth exploring IMHO).

    September 23, 2019 at 4:29 pm

  9. Shelley

    Mary we have this deer hanging around the yard. This is the 2nd year we’ve seen her and they are eating the acorns under our big oak trees.

    September 24, 2019 at 7:13 pm

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