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#Ascension definition astronomy plus#

It remains fixed hour after hour, night after night. One particular star convenient for measuring Earth position is the North Star or Polaris. Those stars reached their maximum altitude, you would then know your latitude. On a sailing ship and had a list of declinations of brightstars and measured when Latitude of the observer and is known as declination. That maximum altitude is equivalent to the

In this coordinate system, an observer at some latitude would observe that any star Would have the same declination as the observers latitude on Earth. Projections of Earth's north and south pole. These are also projections of Earth's North and South poles into the sky.Ĭelestial coordinates are defined as a system where the celestial equator is a projection of the Earth's equator. North and South celestial poles are +/- 90 degrees from the celestialĮquator. This improved coordinate system defines a celestial equator as a projection ofĮarth's equator in the sky. Than a multitude that depend on location and time on Earth.Ĭelestial Coordinate System - RA and Declination Thus Rigel can have one coordinate associated with it rather Independent of an observers location on Earth. However, for modern astronomers it is infinitely more convenient to define a coordinate system Useful coordinate system to measure the position of Mars night after night from one location on Earth. The viewing direction is the same in the sky yet the Alt-Az coordinates and position of Rigel are different.įor early astronomers like Tycho Brahe, this was a Stellarium show Alt-Az coordinates of Rigel taken at the exact same moment in Calgary and Los Angeles.

It should be apparent that this system is based on the observers location on Earth.

Horizon and moves away from the meridian and is thus setting. As the starĪpproachs the meridian it is still "rising" at the meridian its at its highestĪltitude in the sky as the star continues its motion it approaches the western

The meridian is an imaginary North-South line running through the zenith.

The star in the diagram has an (estimated) altitude of 45 degrees and azimuth of about 120 degrees.

The south east would have an azimuth of 135 degrees. Yes, north can be defined as 0 or 360 degrees.

Azimuth is the coordinate direction that runs parallel to the horizon and rotatesĬlockwise from north (0 degrees) to east (90 degrees) to south (180 degrees) to west (270 degrees)īack to north (360 degrees).

When the star is directly overhead at zenith, that angle is 90 degrees. ground) which corresponds to the angle between the starĪnd the horizon.

A star will rise in the east and set in the west and at any given time it will.

Imagine a line from the center of the Earth that continues through the observers's body through the top of the observer's head.

Directly overhead the observer is zenith.

The radius of the earth is a lot bigger than your height of 1.8 meters, this This model assumes that the earth is flat (with respect to the observer) and since The disk the ground and the perimeter defines the horizon.

In this diagram, an observer is standing in the middle of the hemisphere shown above.

System for observing the motion of a star is shown below:

#Ascension definition astronomy plus#

Hence our coordinate system for events consists of a location plus a time otherwiseįor an observer standing on the surface of the earth, the simplest possible coordinate Still nothing happens because you have not specified a time, only a location. That occurs at a specific time in a specific place.įor instance, if you text message your friend the following: Events don't occur without a coordinate system because an event is something Without a coordinate system and measurements don't mean anything without a coordinate Motion has no meaning with out a coordinate system.