View Single Post
JeffOCA
#1
Mar10-12, 07:12 AM
P: 49
Hi,

When you have to calculate the rising or setting time of a celestial body, you have to handle with hour angle and sidereal time.

Sidereal time for the rising is given by T = alpha - H and by T = alpha + H for the setting (alpha = right ascension). Why - H in one hand, and + H on the other hand ?

Maybe because :
1/ hour angle H is computed from east toward west, so H=0 when crossing meridian, in south direction. Before crossing meridian, H = - [itex]\left|H \right|[/itex] so it's negative and it is positive after meridian is crossed H = [itex]\left|H \right|[/itex]
2/ we can say that rising and setting are symmetric with respect to meridian transit, which occurs when T = alpha (i.e H=0)... so -H for rising and +H for setting

Which explanation is better ? If none of them, could you explain the right way ?

Thnaks
Phys.Org News Partner Astronomy news on Phys.org
Chandra X-ray Observatory finds planet that makes star act deceptively old
Astronomers release most detailed catalogue ever made of the visible Milky Way
Planets with oddball orbits like Mercury could host life