Stellarium

how to find the aphelion

Asked by Marco

in Stellarium is it possible to see in wich day of the year the sun is in the aphelion point respect the Earth, even for a year before Crhist (for exemple -508)? Thank you in advance

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gzotti
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gzotti (georg-zotti) said : 		#1

Not directly. You can just read distance, but note that this distance is to your location, not earth's centre.

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Marco (mmontagnino) said : 		#2

I'm not an astronomer and I know a little about astronomy. I'm reading an
antique manuscript and It says something like the charriot of the sun (or of
the planet Venus) on the ecliptic accelerate and I've read about the changing
of the angolar speed on the ecliptic, that's why I supposed to use the
Stellarium to verify if I could find the date of this speed change.How may I
find it? Please would you explain me, knowing the distance, how may I know
when, from my position, the sun (or another planet) pass the aphelion so that
it start going (apparently) faster. I hope I made the question in the right
way. My English is a bit "rusty".
Thank's you in advance
Marco Montagnino

>----Messaggio originale----
>Da: <email address hidden>
>Data: 07/01/2015 23.01
>A: <email address hidden>
>Ogg: Re: [Question #260311]: how to find the aphelion
>
>Your question #260311 on Stellarium changed:
>https://answers.launchpad.net/stellarium/+question/260311
>
> Status: Open => Answered
>
>gzotti proposed the following answer:
>Not directly. You can just read distance, but note that this distance is
>to your location, not earth's centre.
>
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Best gzotti (georg-zotti) said : 		#3

Antique views and models of the solar system did not assume orbital speed changes, so it's likely not aphelion you are after, but retrograding points of the planets. For Venus, there are maximal angular separations (elongation) from the sun, these are easily observable turning points. The Observability plugin provides dates for maximum elongations for each year.
Depending on the age of your manuscript, astronomical knowledge was different. It was known to Ptolemy that there was a slight speed change (Equation of time) of the apparent sun compared to a mean sun. This was modelled by an eccentric orbit of the Sun around the earth. Details: Almagest. But this is 2nd ct AD, not -508.

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Marco (mmontagnino) said : 		#4

thank you very much!