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Curious: Is there planetary parallax?

6 replies to this topic

#1 wedgeforastroscope

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Posted 02 August 2020 - 06:59 AM

hypertheticall question:

Let's suppose that a person (at the South Pole) while viewing the heavens looks at Saturn and at arms length, Saturn is one fist above the horizon.  Same person does likewise with Jupiter, and at arms length Jupiter is a fist and a half above the horizon.

Now let's suppose another person (at the North Pole) while viewing the heavens, looks at Saturn and lo-behold, at arms length, Saturn is one fist above the horizon.  Same person does likewise with Jupiter, and at arms length, (question) will Jupiter be a fist and a half above the horizon?

Assume that both persons have same arm length, fist size, whatever else and of course assume that the earth's axis of rotation was perfectly set up so that Jupiter and Saturn could be observed from both poles.  Assume that the horizon at the poles are both flat & level.

WFAS

Edited by wedgeforastroscope, 02 August 2020 - 10:38 PM.

#2 StarBurger

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Posted 02 August 2020 - 07:36 AM

Ignoring atmospheric effects it would be impossible to see Jupiter and Saturn above the horizon from the N and S pole at the same time regardless of arm length or fist size.

If they are above the horizon seen from the S pole, they will be below the horizon seen from the N pole and vice versa.

If the planet was exactly on the celestial equator and again no atmoshere  then it might be possible to see it from N and S poles on respective horizons.

There is indeed an element of planetary parallax that will make their positions against the stars different by fractions of an arc second

The parallax error would be the angle subtended of a triangle with base 8,000 miles (the diameter of the earth) and sides of say 1000 million miles ( an average guestimate of the distance of the planet at the time). VERY, VERY TINY.

If this is a trick question do I pass?

#3 Jon Isaacs

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Posted 02 August 2020 - 07:42 AM

I calculate that with a baseline of 8000 miles and current distance to Jupiter of 625,000,000 Kilometers, the angle is 4.25 arc-seconds.

Jon

#4 Cames

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Posted 02 August 2020 - 08:16 AM

Parallax of a sort was seen in a past occultation of a star by Pluto which is a mere 5-1/2 light hours from Earth.  Pluto itself covered the star from Earth's vantage point. However, due to Pluto's atmosphere, some of the starlight was refracted so that the star only appeared to dim for a short period during the occultation..

The dimming effect was not visible uniformly across the whole nighttime hemisphere but rather the effect varied according to the observer's latitude.  I'm guessing the swath of the hemisphere where occulting effects were noticeable was maybe less than 3000 miles wide.

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C

#5 csrlice12

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Posted 02 August 2020 - 11:32 AM

I donno, but I do shake my fist at the sky....mostly because I can't see Jupiter, Saturn, or even stars.

#6 B l a k S t a r

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Posted 02 August 2020 - 12:40 PM

I donno, but I do shake my fist at the sky....mostly because I can't see Jupiter, Saturn, or even stars.

That's because your icon is an ode to a cloud.

#7 Cotts

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Posted 02 August 2020 - 05:04 PM

I calculate that with a baseline of 8000 miles and current distance to Jupiter of 625,000,000 Kilometers, the angle is 4.25 arc-seconds.

Jon

^This^  If you were on Jupiter the Earth would be a tiny ball of 4.25 arc-sec diameter...

Dave

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