Planetary Exercise

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DRatledge
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Planetary Exercise

Post by DRatledge » Tue Mar 31, 2020 11:57 am

How far away is the minor planet ERIS? This was an exercise I set recently for Bolton School Astronomy group. Its distance can be estimated with simple maths using the image below. This is a composite of two images taken 4 days apart and ERIS is shown in its two positions. The answer is in Astronomical Units (AU) ie the Earth to Sun distance. You will need a calculator with tangents but apart from that it should be straight forward.

Tips: assume the movement shown in those 4 days is down to the movement of only the Earth ie parallax. Assume the movement of the Earth is in a straight line. Both these are not quite correct but will get an answer with an error of about 10%. This is good enough to give an indication of how far away it is. For comparison Pluto is 34 AU away.
Have fun!
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eris-negative-scale.jpg
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PMiskiw
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Re: Planetary Exercise

Post by PMiskiw » Sat Apr 04, 2020 4:09 pm

David,
I was pretty good at trig when younger so using Tangent = opposite over adjacent can you provide answer please.
Also what is the significance of the colour green in your picture of the comet ATLAS.
Peter.

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DRatledge
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Re: Planetary Exercise

Post by DRatledge » Sun Apr 05, 2020 9:51 am

Peter,
I did give some big clues as how to calculate it and I cannot really spell it out without spoiling it for others. Remember I said assume Eris hasn't moved - you can also assume the background stars haven't moved so all that has moved is the Earth. If you draw a plan of that then it should become clear. Oh and you need to know the circumference of a circle. The error from the assumptions is around 15% rather than the 10% I said but still shows how far away it is - Pluto is nearby!

Comet Atlas is green from carbon. Latest news I saw about it was that it was now fading so perhaps will not become visible.

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Re: Planetary Exercise

Post by DRatledge » Sat Apr 18, 2020 5:15 pm

eris-plan.jpg
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If you haven't solved it then I hope this drawing should explain how to do it. Because of the crude assumptions the answer is 15% too big but does show that Eris really is Extremely Remote In Space.

Peter - the images I take are what I am interested in and have read about.

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