On Earth,longitude is measured positively eastward. Astronomers measure Right Ascension of the stars positively in the same direction but measure the angle in units of time. once around the celestial equator is 24 hours,once around the Earth's equator is 360 องศา,since,in angular terms,24 hours is 360 องศา,there is a numerical ratio of 1:15 between them. In one minute of time, the Earth has spun 15 minute of arc on its own axis Navigators take their Sidereal Hour Angle positively in the opposite direction but keep in units of degrees,and that is what you will see in the tables