Re: RA question

On Mar 5, 4:55 am, "oriel36" <geraldkelle...@xxxxxxxxx> wrote:
On Mar 5, 8:15 am, "canopus56" <canopu...@xxxxxxxxx> wrote:





On Mar 3, 2:01 pm, Eric <N...@xxxxxxxxxxx> wrote:

If an object is at RA x:yy for example, how do i know where it is in the
sky? I cant figure out how to use RA to determine a point in my view of the
sky.

Your current local sidereal ("cy-dear-e-el") time (LST) can be found
at this handy USNO web applet:

http://tycho.usno.navy.mil/sidereal.html

LST means the right ascension that is currently transiting your south
meridian. You can also follow LST with a planisphere. Orient the
planisphere to the current time. The RA (that corresponds to the
current LST) can be read off the dial plate along the noon-midnight
line.

I found spending a couple of days with my plainisphere, following the
rotation of celestial dome throughout an entire day - including
daylight - helped me to wrap my head around the concept of LST. The
analogy mentioned in this thread about sidereal time as a watch that
runs 3 minutes and 56 seconds fast is a good one.

Why 3:56 minutes fast? If the Earth were just hanging motionless in
space rotating on its axis, the solar day would have a nice equal 24
hours periods. But the Earth also revolves around the Sun. Because
the Earth also is moving along a tangent to its solar orbit, the Sun
gets to back to local solar noon 3:56 minutes "faster". The 3:56
minutes represents the linear travel of the Earth in its orbit around
the Sun.

Enjoy - Canopus56

.
and Oriole enjoins:

The real bonus is appreceating how clocks were developed to keep in
sync with axial rotation when it was promoted by Copernicus as the
cause of the daily cycle.

Honor Copernicus by not mentioning his name.

Ben

.

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