# Talk:Hour angle

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## Meridian

Looking at the definition of the meridian it seems to be a great circle, therefore any object is going to pass through the meridian twice in a 24 hour period. I assume the hour angle is measured from when the object crosses the meridian below the celestial pole rather than above it? If this is the case the article needs to clarify this point. Htaccess 13:06, 9 May 2006 (UTC)

It looks like Culmination makes this distinction, so the question become is the hour angle measured from when the lower or upper culmination occurs? Htaccess 13:32, 9 May 2006 (UTC)

## East or west?

The article states: "For example, if an object has an hour angle of 2.5 hours, it transited across the local meridian 2.5 hours ago (measured using sidereal time), and is currently 37.5 degrees west of the meridian." Should this not be east rather than west as in the northern hemisphere objects rotate the pole in a counterclockkwise direction therefore two hours after crossing the meridian it will be to the east of the meridian and not west. Likewise in the south stars rotate clockwise round the pole therefore an object will be to the east of the meridian. In fact should compass points be used at all as the direction will be changing over time, would it not be better to use clockwise and counter clockwise to describe rotation? Htaccess 13:06, 9 May 2006 (UTC)

Short answer... no. Think about it for a moment. You know that the sun, moon, and stars rise in the east, and set in the west -- so they're always moving west when they're above the horizon. Of course, there are the stars near the poles that never set, or go for months without setting, but since we're talking about the time period 2.5 hours after transiting the meridian, we can also say for sure that one of those objects is traveling west at the time. 67.95.66.69 21:59, 28 November 2006 (UTC)

## Relation with sideral time

Isn't the hour angle defined as the angle between the local meridian plane and the plane passing through the polar axis and the star? And, as such, it is an alternative to the right ascension in the equatorial coordinate system? And then the sideral time is defined as the hour angle of the vernal point? Rlupsa 18:53, 3 October 2007 (UTC)

Yes, those statements are all correct. Sidereal time is the hour angle of the vernal equinox - Jthorstensen (talk) 00:24, 8 December 2007 (UTC)

## Graphic Illustration

Some graphical illustration might be extremely helpful. — Preceding unsigned comment added by 46.126.159.162 (talk) 10:45, 28 January 2012 (UTC)