How does Right Ascension and Declination work to find objects in the sky?

Answer 1

It's basically the same concept as longitude and lattitude, except in reverse, you are looking up at the sky.

They assign a positioin in Right Ascension (0h0m0s) to a point in the sky (that can include stars or the sun or the moon) and declination.

Then they use that point to measure all other fixed object (stars and galaxies).

So, you go out at night and find an object you are sure of that is fixed (a nice, bright star you know for sure, like the stars in Orion in winter time for example, pick one, look up it's RA and Dec) and then you can use your setting circles on the telescope to find other objects that are harder to see with the eye.

It, in essence, requires you know the RA and DEC of objects and know a few fixed objects.

Moving objects, like Urnaus and Neptune are predicted math wise and published in ephemeris tables.

So you find a fixed star by RA and DEC and then you move your scope to the ephemeris setting for Uranus by RA and DEC and you should be right on that very dim object that can only been seen in a mid-size telescope.

Answer 2

Right Ascention (R.A) and Declination (Dec) are the celestial counterparts of the Terrestrial coordinates of Latitude and Longitude and are used to find objects in the sky instead of on earth.
The terminology is a little different, but the process is the same.
R.A. is the equivalent of Longitude and is measured in Hours, Minutes and seconds.This is a little strange at first, but makes sense if you think of the fact that longitude can also represent time. Your Time zones are based on it. Each 15 degrees longitude equals 1 Hour. It is noon in the Eastern Standard time zone 5 hours after it was Noon At Greenwich. That means by the time it gets here the sun will have travelled 75 degrees around the world.
Just as they did with Greenwich Mean Time (or UT) a point was picked by international agreement to serve as the starting point.
If a star appears over greenwich four hours after a star at the starting point it'S R.A. will be 4hrs 00min 00 sec. Written R.A. 4:00:00.
Declination is nothing more than the Line of the Equator projected into the sky, as if a slide projector projected the latitude lines onto a ceiling overhead.
Just like a regular Map, a star Atlas or chart will show the coordinate lines in a grid and by knowing the celestial coordinates of an object at any given time ( remember there are many things in the sky that are moving, and tables are published for these objects) you can locate it anywhere in the sky, just like, by knowing your own coordinates, you can find your house on any map of the area.
Just as a note: Historically 99% of Astronomical work was done for the purpose of navigation on Land or Sea so it is not surprising that Navigation Terminology is used for some items related to this.

Adolph

Answer 3

It works exactly like longitude and latitude to find objects on Earth. And just about as useless too. In the fifty years I've been an amateur astronomer, I've hardly ever met anyone who actually used RA and Dec to find things.

When you want to visit a friend's house, you don't find out it's longitude and latitude; you either look at it on a map or get directions. And that's exactly how amateur astronomers find things: by looking at a star atlas or by using "starhopping" directions in a book. At least, that's what I've done until recently. Now I use digital setting circles or GOTO to locate dim objects, and often I have to enter their RA and Dec to get there.

Answer 4

Astronomy has created an imaginary sphere with the Earth being the Center of this Celestial sphere.So we can match a point on earth to a point on the celestial sphere in terms of coordinates. These cordinates are measured angles on the sphere.The reference points on the sphere is a point of measurement which matches the rotation of the earth in terms of time which on earth we call longitude.On the celestial sphere instead of degrees,hour,minutes and seconds of time is used and are measured to the right of the zero reference point(right of ascension.)
Latitude on the celestial sphere is measured just like on Earth ,in degrees relative the celestial pole called nadir(declination).
This is the system used to locate celestial bodies.