Re: R.A and Dec question

Thank you for that wonderful explanation Carsten.

Now here is the justification in graphic terms -

http://www.pfm.howard.edu/astronomy/Chaisson/AT401/IMAGES/AACHCIR0.JPG

Can you please explain to the original poster why you believe in a
system where the Earth covers a greater distance in its orbital
circumference the further from the Sun it is.Just put the sidereal
justification in an elliptical framework to affirm this unsightly
spectacle.

The actual relationship between clocks,terrestial geometry and
astronomy is complicated and goes back to remote antiquity.The most
important and the most historically visible complimentary addition
was the application of the Equation of Time principles of the 24 hour
day to axial rotation at 15 degrees per hour.The point being that to
justify an Ra/Dec system astronomically is fatal to astronomical
principles and indeed all else.






Carsten A. Arnholm wrote:
Steven Gill wrote:
Could someone please point me to a good tutorial for working out R.A
and Dec? For example I saw in a magazine article that M4 can be found
at R.A 16h24m Dec -26. 32 How do I go outside and point my telescope
at R.A 16h24m Dec -26. 32 ?

Any help very much appreciated!!

Steve

Hi,

http://liftoff.msfc.nasa.gov/academy/universe/RADEC.HTML
http://en.wikipedia.org/wiki/Right_ascension

R.A stands for "right ascension" and Dec stands for "declination". It is a
coordinate system which for all practical purposes stays fixed relative to
the stars, and therefore appears to be rotating around the earth once per
(sidereal) day. Of course, this is because the earth rotates around its own
pole-to-pole axis in the opposite direction. So if you want to point your
telescope to a particular point measured in RA and DEC, you must also take
the observation time into consideration in some way.

There are several ways this can be done in practice, depending on your
equipment. But often it means you must

a) Assuming you have an equatorial mount, you should polar align your mount
http://arnholm.org/astro/polar_alignment/ .

b) Find a bright star, near the relevant position, on a star chart. Find
that star in the sky and point the telescope to it. Adjust the setting
circles on the mount to show the coordinates of that star.

c) Move the telescope until the setting circles show the positions you want,
and M4 should be in your field of view.

Of course, this can be done using GOTO or other methods. I use a method
similar to the above, but instead of using setting circles, I have written a
PC program to do the GOTO job.

Clear skies
Carsten A. Arnholm
http://arnholm.org/
N59.776 E10.457

.

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