JNow or J2000 ?

[Shano592]

Hi All,

I have been playing around with Starry Night, and when you highlight a DSO, it gives 2 sets of RA/Dec figures, amongst all of the other information.

The first is J2000, and the other is JNow. Which do you use, when hunting manually? I am assuming it is the latter, because of the name, but I would greatly appreciate a definitive answer.

Thanks in advance.

[Jeff]

Hi Shane,

You are correct in assuming that JNow will provide the more accurate co-ordinates, but the difference between JNow and J2000 (typically only about 1 arc minute) is pretty small. J2000 figures are published in lots of current day books, and the IAU is expected to switch epoch J2050 figures sometime down the track.

If you're aligning manual setting circles using a known star (eg. Sirius), then it really doesn't matter which you use, so long as you're consistent.

Hope this helps.
Jeff