Wolfram Alpha's query: Sun Earth distance in AU gives:

1.012 au (astronomical units)

They definitely use this value in other places too - e.g. Earth-Sun $L_1$ distances from Earth and from Sun don't add up to 1 AU - they are 0.01009 AU and 1.001 AU respectively.

Contrarily, Google gives Earth Sun distance in AU = 1.000 AU.

The top search results for Sun Earth distance 1.012 AU yield a page with a big heading of "Paranormal UFO Aliens Wow!".

Is the 1.012 AU value an error in Wolfram Alpha, or is it some little-known adjustment, redefinition or other quirk of the unit or the Solar System?

  • $\begingroup$ Bottom line: While you have to be careful of what you ask WA, you have to be even more careful of what you ask of search engines such as Google that explicitly say that they tailor their searches to you just so they can pitch the ads to which you are most likely to respond. $\endgroup$ – David Hammen May 18 '16 at 14:14
  • $\begingroup$ As a further aside, one needs to be cognizant of John Searle's ~36 year old Chinese room argument when it comes to asking computers questions. For now, search engines such as Google and automated question answerers such as WA sometimes arrive at incredibly inane results because the techniques they use are the embodiment of Searle's "Chinese Room" argument. $\endgroup$ – David Hammen May 18 '16 at 14:30
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    $\begingroup$ "Originally conceived as the average of Earth's aphelion and perihelion, [the astronomical unit] is now defined as exactly 149 597 870 700 metres." From the Wikipedia page for "Astronomical Unit". $\endgroup$ – Todd Wilcox May 18 '16 at 19:11
  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$ – called2voyage May 19 '16 at 1:50
  • $\begingroup$ @ToddWilcox: Interesting caveat of that: averaging the distance over time would yield a higher number, as orbital mechanics make Earth spend more time on the apoapsis end of the orbit. $\endgroup$ – SF. May 19 '16 at 17:40

As of this moment (2016 May 18, 13:15 UTC), the Earth is 1.0116 astronomical units from the Sun. WA is smart enough to know that "Sun Earth distance in AU" is a time-dependent question.

Update: The stricken text that follows from my original answer is incorrect. I am leaving it present (but stricken) for the sake of humility.

It interpreted your query to mean Sun Earth distance today in AU, and because today is 2016 May 18 and because you didn't specify a time of day, it picked noon (UTC), it in turn interpreted your query to mean Sun Earth distance on 2016 May 18 at noon UTC in AU.

The correct answer: I happened to ask WA the very question posed in the OP a couple of minutes apart and got two different answers (1.014 and 1.015 AU), and this did not occur across a day boundary. WA apparently interpreted your query to mean the current distance between the Sun and the Earth.

You have to be very careful of what you ask WA.

A better query is to ask WA What is the mean distance between the earth and the sun in AU? That query will give you an answer of 1.0000010178 au. An even better question is What is the semimajor axis of Earth's orbit? That will give you an answer of 1.00000011 au. Note the extra zero, but also note that for some reason, the precision is reduced.

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    $\begingroup$ ...note to self: check in a couple months if you were right. $\endgroup$ – SF. May 18 '16 at 19:47
  • $\begingroup$ @SF. -- That is a good note to self, and also to me. It shouldn't take a couple of months. If I am correct, all it will take is another week or so before asking WA what the distance between the Earth and the Sun results in a value of 1.013 AU (or more). But don't wait past the Fourth of July, which will be when the Earth is furthest from the Sun (this year, that is). $\endgroup$ – David Hammen May 18 '16 at 19:58
  • $\begingroup$ If my answer is correct, all that you will have to do is wait until 23 May (or possibly 24 May, depending on where you live) and see that the WA answer changes from 1.012 AU to 1.013 AU. $\endgroup$ – David Hammen May 18 '16 at 20:03
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    $\begingroup$ @SF. -- I forgot I was supposed to double check this answer on 23 May. I checked it just now, (2016 June 03 23:44 UTC), asking WA to tell me the "Sun Earth distance in AU". The answer was 1.014 AU. I double checked before clicking on "Add Comment" and the answer became 1.015 AU. I need to update my answer. Apparently WA interprets "Sun Earth distance in AU" to mean "Sun Earth distance in AU now". $\endgroup$ – David Hammen Jun 3 '16 at 23:49
  • $\begingroup$ To add to David's anwser: the modern definition of the Astronomical Unit is no longer linked to the Earth's orbit. It is defined as exactly $149\,597\,870\,700$ metres, regardless of the actual orbit of the Earth. $\endgroup$ – Pulsar Jun 5 '16 at 18:19

I searched the same thing and Wolfram returned the following note:

Assuming "earth" is a word | Use as a planet instead

And so I did, and when searching for the distance from earth to the sun using earth as a planet, Wolfram returned a list of earth's orbital parameters in the bottom of the page.

In this list of parameters, I clicked in the link "sources" to see where this data was coming from. Among the sources was this JPL website with all sort of solar system data you can imagine.

So I think that Wolfram either connects to JPL's website to get the sun-earth distance in real time or uses their tables to calculate it.

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The earth sun distance is complex. So, as was said, is date specific. An AU is 'average' distance of a mean tropical year. And the earth's elliptical orbit is complicated in that the earth/moon barycenter orbits the solar system's barycenter. So the distance between barycenters may also be a matter of precision depending on the application.

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