![]() Like cities, every object in the sky has two numbers that fix its location called right ascension and declination, more generally referred to as the object's celestial coordinates. Detroit, Michigan, is shown here.ĬC 3.0 / Wikipedia Right Ascension & Declination Every location, whether it be a city, airport, or even your own home or apartment building lies somewhere on the worldwide coordinate grid (below), its location fixed by two numbers.Įvery city on the planet has a unique latitude and longitude, its "spot" on the grid. A negative sign in front of the latitude indicates south and a positive sign north. Or Wonglepong, Australia, situated along that continent's east coast at –27.0° south, 153.2° east. Take Tuscaloosa, Alabama, for example, which is located at latitude +33.2° north, longitude 87.6° west. ![]() It defines the the zero (0°) longitude line just as the equator defines the 0° latitude line.Įach city has a unique latitude and longitude. The prime meridian is an imaginary line that runs through the Royal Observatory in Greenwich, United Kingdom, and extends to the North and South Poles. To find anyplace on the globe of Earth, you only need to know its latitude, the distance in degrees north or south of the equator, and longitude, the distance in degrees east or west of the prime meridian. Then I realized they were just numbers like latitude and longitude, except applied to the stars. When I got started in astronomy at age 11, they were a little scary. Sooner or later every novice skywatcher runs into the terms RA and Dec., short for right ascension and declination. The world population, always galloping.Įarth in crisis, the end of a stable world.The sky is draped in an invisible coordinate grid that will help you easily find any object you wish, the same as you would locate a city on a map. The oldest image never taken of the Earth. Image: The vernal equinox is the equinox in March (early spring in the northern hemisphere, autumn in the southern hemisphere). Sidereal time, one hour is 15 degrees (360 ° / 24 = 15 °). Right ascension is measured as an angle expressed in hours (H), minutes (M), second. The vernal equinox is the equinox in March (early spring in the northern hemisphere, autumn in the southern hemisphere). ![]() The sun moves through these two points of intersection defines the two equinoxes. This is one of two points where the celestial equator and the ecliptic intersect. The point of origin for right ascension is called the vernal equinox. The zero point on Earth is the intersection of the Greenwich meridian and the equator is the point of origin for terrestrial longitude. Just as the longitude of a point on Earth measure the angle between the meridian of that place and a reference meridian, the right ascension of a star in the sky, measuring the angle between the hour circle of the star and circle time reference. As the terrestrial latitude, it is expressed in degrees (°), minutes (') and seconds (") arc, positive north and negative south of the celestial equator. Declination is the angle measured on a circle time between a point on the celestial sphere and the celestial equator. These coordinates are the extension of the latitude and longitude of the earth, projected into the sky, they are used either in equatorial coordinates, or coordinate schedules. To locate the position of the stars on the celestial sphere, we so use the declination and right ascension. The celestial coordinate system works the same way, but the latitude and longitude are called, declination and right ascension. On Earth the latitude measures the distance between a point and the north and south pole, while the longitude is the distance from east to west, compared to a reference meridian. To locate a point on Earth we use latitude and longitude on earth.
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