Home > education, musing > Earth’s aphelion and perihelion

Earth’s aphelion and perihelion

March 12, 2015

Sometimes the stuff I think about gets me down. I mean, jeez, I think about cynical stuff all the time, and I need to rest my brain sometimes.

When that happens, I sometimes fantasize about really long-term things that happen in the solar system or even the universe. It gives me perspective.

One of my favorite videos to watch at these moments is this one, which always blows my mind. The take-away: nothing is permanent unless there is actually a physical law forcing it to be. Here it is:

p.s. I vote for “tropical year” because I love analemmas.

p.p.s. Looking forward to Vega being the pole star once again.

p.p.p.s. This came up because my husband and I got into a conversation about earth’s aphelion and perihelion and we were wondering if it’s just by chance that perihelion happens near the beginning of winter. The answer is yes, because [take-away above].

p.p.p.p.s. How cool is the name “invariable plane”? And how amazing that the period of the orbiting plane of the earth and the period of the axial tilt are different? There’s really nothing that we can rely on, is there?

Categories: education, musing
  1. Josh
    March 12, 2015 at 8:39 am

    Good way to start the day. Thank you.


  2. Josh
    March 12, 2015 at 8:52 am

    The Islamic calendar is 354 days. As a result, unlike most cultures, the festivals have no seasonal associations as they precess through the seasons.


    • March 12, 2015 at 10:13 am

      The Jewish calendar also uses a lunar year, hence 354 days, but to make the festivals seasonal it adds 6 leap months in a 19 year cycle.


      • Josh
        March 12, 2015 at 11:23 am

        Yes, indeed. There are many lunar calendars. So, Passover always begins on Nissan 15 but whether that is in March or April varies. But, it is always in the spring because, as you note, the Jewish calendar offsets the short year with an occasional extra month. Easter and Chinese New Year do the same are set on lunar calendars and do the same.

        The Islamic calendar is the only one I know of that does not have a mechanism to offset the short year. So, Ramadan has shifted from the summer to the winter and back within my lifetime. And, people who account for their ages in Islamic years will be noticeably older than if they used other calendars (whether sidereal, tropical or anomalous).


      • Auros
        March 12, 2015 at 1:46 pm

        The Greeks and Romans did something similar, I think? I seem to recall that they started from lunar months, but then at least some version of the Roman year inserted a variable number of festival days between each pair of successive years, to force the lunar cycle to agree with the sidereal year… I think the Greeks had various versions of waiting a few years at a time to insert a full intercalary month.


  3. March 12, 2015 at 9:23 am

    The video is amazing. All that complexity and all the different cycles. So many variables. Implicitly explains climate change to a great extent.


    • Josh
      March 12, 2015 at 10:06 am

      I don’t know what you mean by “Implicitly explains climate change”. Yes, the cycles it talks about do cause ice ages and other changes in the cilmate. But, the warming we have experienced is occurring at a much faster pace than anything the video discusses.

      If you are saying that we can wait for the 100,000-year cycle to offset the impacts of carbon in the atmosphere, I disagree.


      • March 12, 2015 at 10:10 am

        Listen more closely. It’s not just the 100K year cycles the video talks about. It’s quite complex.


        • Josh
          March 12, 2015 at 11:11 am

          Other than Cathy’s favorite annalemma which does not have a pronounced climate affect and, of course, the elliptical nature of the orbit, I didn’t hear anything that would explain climate fluctuations on the time scale of the warming we have experienced. So, could you explain how this video “implicitly explains climate change”. Perhaps, as you note, I did not listen closely enough.

          Of course, the Earth’s climate is more generally, is quite complex and there are other natural phenomena that cause climate fluctuations. So, the El Nino probably reduced the warming in the past decade. But, are you saying that carbon emissions are not an important contributor to the warming of the past 50 years?


        • March 12, 2015 at 11:13 am

          Abe likes to provoke. I think he means to say that ice ages come and go depending on the periodicity of various things in the solar system. Obviously his use of the phrase “climate change” in this context was intentionally provocative. The climate change we are experiencing here on earth is moving at a much brisker pace than anything with a period of 40,000 years.


  4. Richard
  5. Josh
    March 12, 2015 at 11:27 am


    Re: “Abe likes to provoke”. Apparently, you didn’t listen closely enough to the video, either.

    Abe will enlighten us.


  6. Auros
    March 12, 2015 at 1:54 pm

    One thing that’s not remarked on in the video — my understanding is that the current arrangement of the seasons, with the southern hemisphere getting the “double whammy” of being tilted towards the sun while we’re closer to perihelion, is significantly offset by the fact that the southern hemisphere has a lot more ocean, and the thermal mass of all that water serves as a buffer. And that’s the main reason that seasons in Argentina or New Zealand don’t particularly look more extreme than at corresponding northern latitudes. In fact, the most extreme seasons happen in places that are far from big masses of water, like central Asia. Ferinstance:


    Summer temperatures occasionally reach +35 °C (95 °F) while −30 to −35 °C (−22 to −31 °F) is not unusual between mid-December and early March.


    • Auros
      March 12, 2015 at 1:56 pm

      Inland Canada is another good place to look for wild temperature swings.


      The lowest temperature ever recorded was −50.0 °C (−58.0 °F) on 1 January 1885, while the highest recorded temperature was 43.3 °C (109.9 °F) on 5 July 1937.


  7. Jim
    March 12, 2015 at 3:24 pm

    Here’s another YouTube in a similar vein, “The Galaxy Song”:


  8. Josh
    March 13, 2015 at 9:52 am

    Jim, Thanks. Another good way to start the day. Josh


  9. Min
    March 13, 2015 at 10:25 am

    In the long run we’re all angel dust. 🙂


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