How to find Earth/Sun Distance on a certain day?

Question

I need to find some tool where it is possible to calculate the distance between the earth and sun on any given day of the year.  So far I've been unable to find such a tool through several Google searches.  Does anybody have a software program or website that they can refer me to?  For example, I would want to know "On July 8th the sun is x miles from the Sun", or any other date I chose.  TIA!

bikenbeer2000 · Accepted Answer

NASA's Horizons website will give you this information to a very high degree of accuracy:
http://ssd.jpl.nasa.gov/horizons.cgi
As an example, if you set the following parameters, you will obtain the Sun's distance on every day of the year for 2012:

Ephemeris Type [change] :  	OBSERVER
Target Body [change] :  	Sun [Sol] [10]
Observer Location [change] :  	Geocentric [500]
Time Span [change] :  	Start=2012-01-01 00:00, Stop=2012-12-31 00:00, Step=1 d
Table Settings [change] :  	QUANTITIES=20
Display/Output [change] :  	default (formatted HTML)

The distances are given in Astronomical Units, so multiply by 149,597,871 to convert to kilometres or by 92,955,807 to convert to miles.
To take your example of July 8th, in 2012 the distance is 1.01666071055426 AU, which is 152,090,278 km or 94,504,517 miles.

If you don't need quite this accuracy, try http://www.fourmilab.ch/cgi-bin/Solar/action?sys=-Sf

Anonymous · Answer

Use Aryabhatta Astronomy Theory

? · Answer

This website has exactly what you need, along with equations and how to use them=>http://curious.astro.cornell.edu/question.php?number=582

Angela D · Answer

if you can't find it in _astronomical algorithms_ by meeus, you don't need to know it. :-)

vsop87 is a good model for this.

how accurate do you need your results? is an unperturbed elliptical orbit good enough?

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How to find Earth/Sun Distance on a certain day?

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