Question Regarding Dec and R.A.

When I read a Dec and RA for a star or object in some book or magazine, I know I can go to my star atlas and find that coordinate. It doesn't matter what time of night or my location.

But a given Dec and RA for a planet or comet or astroid is different. How do I find a planet, such as Neptune, from a published Dec and RA. Do I need to know GMT and subtract my time? Where do I go from there. Have I opened a can of worms :S

Thanks

DCR

Hi David,

Not a can of worms. But it does sound worse than it really is.

RA and DEC of a star don't change in books and magazines that are recent publications. But if you looked at a star atlas from 25 or more years ago the RA and DEC of a star would be different. So stars coordinates do change, but very very slowly.

But planets and asteroids move quickly, relative to the stars, so their coordinates are only good for a certain date and time.

In the magazines, you might see Jupiter will be at some RA/DEC at 0600 UT, or "universal time" (a terrible term!). You need to convert UT to local time, then go look at that RA/DEC around that time. There are plenty of websites to help convert UT to local time. But, for example, if you were in Boulder Colorado, then 0600 UT would be midnight local time (Boulder is 6 hours behind UT during daylight savings time)

sf