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Thread: Perihelion and orbital mechanics

  1. #1
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    Question Perihelion and orbital mechanics

    1. It is often stated that the dates of perihelion and aphelion change over time and make one complete cycle every 22,000 to 26,000 years. This is because of earths precession. My question is if an arrow was drawn pointing from the sun to the earth on the moment of perihelion and that arrow, if continued out, would point at some galaxy "X" would that arrow still (ignoring galatic motion) point to galaxy "X" 10,000 years later at the moment of perihelion?

    2. Is there both rotational AND revolutional precession of the earth. If so; what is the duration of the later?

  2. #2
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    The rotational precession is something we calculated in Physics One, when studying gyroscopic motion. What you are calling revolutional precession is mostly a result of the impact of Jupiter's gravity on the Earth's orbit, and yes the direction of perihelion does change with respect to distant objects.
    Forming opinions as we speak

  3. #3
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    Quote Originally Posted by antoniseb View Post
    The rotational precession is something we calculated in Physics One, when studying gyroscopic motion. What you are calling revolutional precession is mostly a result of the impact of Jupiter's gravity on the Earth's orbit, and yes the direction of perihelion does change with respect to distant objects.
    From the difference between sidereal and anomalistic year as published in Norton's Star Atlas, I get 114,000 years +or- 3000 for a complete perihelion advance cycle. That line of sight will migrate eastward along the ecliptic from its current position in Gemini.

  4. #4
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    This wiki
    http://en.wikipedia.org/wiki/Apsidal_precession
    says that the dates of perihelion varies over a cycle of 21,000 years. And the rotation of the ellipse (or, that "arrow" in the OP) has a 112,000 year period.

  5. #5
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    The sun crosses the perihelion point on about 3 January each year. Perihelion passed the December solstice point in about 1296 AD due to apsidal precession. The interaction of the rotation of earth's orbital ellipse and the precession of the equinox is a primary driver of the ice age period of about 21640 years, the period it takes for a solstice to travel all the way around the ellipse. See http://en.wikipedia.org/wiki/Apsidal_precession

    http://individual.utoronto.ca/kalend...ons.htm#eccent states "At the present mean rate of about 11.6 arcseconds of advancing heliocentric longitude motion relative to the distant stars (eastward) per year, perihelion takes about 111,700 years to revolve once around Sun. At the same time, however, the northward equinox is precessing at the rate of about 50.3 arcseconds of ecliptic longitude per year (retrograde, or westward) or one cycle per 25,765 years, due to Earth wobbling on its axis like a spinning top, so the net effect (50.3+11.6 = 61.9 arcseconds per year) is that perihelion advances about 1 per 59 years and therefore takes about 360 59 ≈ 21,240 years to revolve once relative to the northward equinox of the date, advancing through all of the seasons in sequence."

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