I would like to check in which constellation the Sun was in at some time in the past, any recommendations how to do that?
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$\begingroup$ Do you mean spatially? Or directionally from our current position? Constellations are defined as relative to our view, so changing our view will essentially destroy the relative view that results in our constellations. $\endgroup$ – Mitch Goshorn Jun 26 '15 at 9:00
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$\begingroup$ from our current position earth $\endgroup$ – user7549 Jun 26 '15 at 9:12
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1$\begingroup$ i will use the software stelarium.. thanks. regards $\endgroup$ – user7549 Jun 26 '15 at 9:50
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$\begingroup$ you might consider accepting one of the answers if you think it's appropriate $\endgroup$ – uhoh May 2 '16 at 12:38
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There are plenty of online planetarium sites which should be able to do this for you. This one is the first hit for a Google search for "online planetarium software"
answered Jun 26 '15 at 8:31
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$\begingroup$ thank you this one's great except i cant see the sun because it hasn't rise at the time, do you perhaps know of some online website that shows the whole celestial sphere from inside? thanks again... $\endgroup$ – user7549 Jun 26 '15 at 9:13
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$\begingroup$ @user7549 You could keep the time but flip your location to the daylight side of the world, the Sun will still be in the same place against the fixed stars. Or use one that will allow you to look below the horizon (the one I have on my android tablet allows that). $\endgroup$ – Conrad Turner Jun 26 '15 at 9:18
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$\begingroup$ i think i cant see the land below horizon..anyway i will use the software stelarium. thanks. regards. $\endgroup$ – user7549 Jun 26 '15 at 9:49
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1$\begingroup$ In Stellarium, you can disable the land (and the horizon,...) and can e. g. enable constellation lines with the buttons on the lower left. $\endgroup$ – hiergiltdiestfu Jun 28 '15 at 9:53
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1$\begingroup$ @uhoh No, I'm just reporting it as the first hit, there are more than you can shake a stick at. $\endgroup$ – Conrad Turner May 2 '16 at 15:50
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- If you're talking about short time periods and don't need a lot of detail, a lookup table such as this one: http://spaceplace.nasa.gov/starfinder3/en/ will work just fine.
- For more detail, you'll have to calculate the position of the Sun on the background stars and determine that moment when the position crosses the (somewhat arbitrarily defined) constellation boundaries. Wikipedia has good introductory equations to determine the Sun's position (https://en.wikipedia.org/wiki/Position_of_the_Sun) though David Colarusso's site has much more information: http://www.davidcolarusso.com/astro/. There are other equations you can use to determine which side of the line the Sun's position lies: https://stackoverflow.com/questions/1560492/how-to-tell-whether-a-point-is-to-the-right-or-left-side-of-a-line.
- For long time periods, you'll have to do what's in the previous point and also determine how the Earth's position changes in relation to the Sun and where in the galaxy the Sun lies. I'll leave that as an exercise for you since I'm not sure you want that level of detail.
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In this case, Wolfram|Alpha has you covered. For example, look at the result for "which constellation was the Sun in Jan 1 1400". That said, I'm not sure this calculate includes the precession of the Earth's rotation axis, since I would've expected it to get my astrological birth sign right in 500 BC.
