fortisi876 wrote in post #15915449
Is it just me or does the photo above appear to have opposing star trail arcs?\
Great photo BTW!
90 deg to the polar axis is the celestial equator, which instead of starts forming circles, they form straight lines....http://en.wikipedia.org/wiki/Celestial_equator
Below should make it obvious.
The celestial equator is a great circle on the imaginary celestial sphere, in the same plane as the Earth's equator. In other words, it is a projection of the terrestrial equator out into space. As a result of the Earth's axial tilt, the celestial equator is inclined by 23.4° with respect to the ecliptic plane.
An observer standing on the Earth's equator visualizes the celestial equator as a semicircle passing directly overhead through the zenith. As the observer moves north (or south), the celestial equator tilts towards the southern (or northern) horizon. The celestial equator is defined to be infinitely distant (since it is on the celestial sphere); thus the observer always sees the ends of the semicircle disappear over the horizon exactly due east and due west, regardless of the observer's position on Earth. (At the poles, though, the celestial equator would be parallel to the horizon.) At all latitudes the celestial equator appears perfectly straight because the observer is only finitely far from the plane of the celestial equator but infinitely far from the celestial equator itself.
So, located in the northern hemisphere, around 42deg, looking North you see this Feb-4-2011
and looking south same night see this
Orion's belt and nebula visible dead center top center of image
a more recent looking south image Dec-12-2012