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saidatta123
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Can anyone explain very clearly(to a n00b like me) right ascension and declination and how to navigate to stars using this system?
Chronos said:Right ascension is the clock-wise [east-west] coordinate due to rotation of the earth. That changes from second to second for all celestial objects.
One simple way to think of it is to imagine projecting the latitude and longitude lines on the Earth onto the celestial sphere. This becomes the coordinate system that is used for defining the positions of the stars. Declination is the analog of latitude, and right ascension is the analog of latitude. Because the Earth is rotating, you have to choose a particular instant to do the projection. We choose to do it at noon in London on the day of the vernal equinox. We also usually measure right ascension using time instead of degrees, with 1 hour of RA equal to 15 degrees, but you can also measure RA in degrees and people often do. As has been mentioned, the RA and Dec of a particular object don't change because of the Earth's rotation, but they do change as a result of the precession of the Earth's axis of rotation. However, this takes 26,000 years to make a complete circle, so the change is slow. For example, here are the coordinates of Aldebaran (Alpha Tauri) in 1950-based and 2000-based coordinates:saidatta123 said:Can anyone explain very clearly(to a n00b like me) right ascension and declination and how to navigate to stars using this system?
BobG was correct. In that part of his post he was talking about hours, minutes, and seconds as they are measured typically. He later gave the reason for that factor of 15.04 degrees versus 15 degrees per hour. One rotation of the Earth with respect to the Sun takes 24 hours. One rotation with respect to the stars takes only 23.9344696 hours. That difference of 3 minutes and 55.9084 seconds between a mean solar day and a mean sidereal day is what results in that factor of 15.04 degrees per (solar) hour.phyzguy said:BobG, let me disagree with something I think you said. Right Ascension can be measured in degrees, or it can be measured in hours, minutes and seconds. The conversion between the two is not approximately 15 degrees per hour, it is exactly 15 degrees per hour. The first one divides the circle into 360 degrees, the second divides it up into 24 hours. It's not correct to say that the conversion factor is 15.04 degrees per hour.
D H said:BobG was correct. In that part of his post he was talking about hours, minutes, and seconds as they are measured typically. He later gave the reason for that factor of 15.04 degrees versus 15 degrees per hour. One rotation of the Earth with respect to the Sun takes 24 hours. One rotation with respect to the stars takes only 23.9344696 hours. That difference of 3 minutes and 55.9084 seconds between a mean solar day and a mean sidereal day is what results in that factor of 15.04 degrees per (solar) hour.
The Equatorial Coordinate System is a method used to locate objects in the sky based on their position relative to the Earth's equator and the celestial equator. It is a type of spherical coordinate system that uses right ascension and declination to pinpoint the location of celestial objects.
The Equatorial Coordinate System is different from other coordinate systems, such as the Horizon Coordinate System or the Ecliptic Coordinate System, because it is based on the Earth's rotation and not its orbit around the sun. This makes it a useful tool for tracking the motion of objects in the night sky.
The Equatorial Coordinate System is used by astronomers and scientists to locate and track celestial objects, such as stars, planets, and galaxies. It also allows for precise measurements and calculations of the positions and movements of these objects.
The Equatorial Coordinate System is measured using two angles: right ascension and declination. Right ascension is measured along the celestial equator, similar to longitude on Earth, and is usually denoted in hours, minutes, and seconds. Declination is measured perpendicular to the celestial equator, similar to latitude on Earth, and is usually denoted in degrees, minutes, and seconds.
Yes, the Equatorial Coordinate System can be used to locate and track all objects in the sky, including stars, planets, galaxies, and even comets and asteroids. However, it is most commonly used for objects that are far away and have a relatively fixed position in the sky, such as stars and distant galaxies.