In the Hour Angle System, a star's position is defined by which two coordinates?

In the Hour Angle System, a star's position is defined by which two coordinates?

• A. Local hour angle and declination
• B. Greenwich hour angle and latitude
• C. Sidereal hour angle and longitude
• D. Polar distance and declination

Answer: (A)

In the Hour Angle System, a star’s position is specified by its local hour angle and its declination. The local hour angle tells you how far the star is from your local meridian, measured westward, so it tracks its apparent movement across the sky from your observing location. Declination is the angular distance north or south of the celestial equator, fixed for the star, placing it above or below the celestial equator. Together, local hour angle and declination uniquely locate the star’s place in the sky from any given observer. The other options don’t fit this system because Greenwich hour angle uses the Greenwich meridian rather than your local meridian, latitude pairs with the observer’s ground position rather than the star’s angular position, sidereal hour angle with longitude isn’t the standard local coordinate pair for the Hour Angle System, and polar distance with declination is a different way to describe a star’s angular distance from the pole rather than its hour-angle position.

In the Hour Angle System, a star’s position is specified by its local hour angle and its declination. The local hour angle tells you how far the star is from your local meridian, measured westward, so it tracks its apparent movement across the sky from your observing location. Declination is the angular distance north or south of the celestial equator, fixed for the star, placing it above or below the celestial equator. Together, local hour angle and declination uniquely locate the star’s place in the sky from any given observer.

The other options don’t fit this system because Greenwich hour angle uses the Greenwich meridian rather than your local meridian, latitude pairs with the observer’s ground position rather than the star’s angular position, sidereal hour angle with longitude isn’t the standard local coordinate pair for the Hour Angle System, and polar distance with declination is a different way to describe a star’s angular distance from the pole rather than its hour-angle position.