Sidereal time = RA of a star + Hour angle of the star
Use this, and knowing your sidereal time - from that star dial - and
knowing the RA/DEC of a star you want to find - calculate the hour angle
and move the rings on your celestial globe, to that location.
First - set your globe to mimic the sky above you. Use the measured
sidereal time, and the fact that
sidereal time === hour angle of the RA=0 meridian !
Then find the star - and then to make sure that you've gotten it right -
use a periscope-like device that points out perpendicular to the surface
of your sphere - and with a little mirror and a hole at the bottom , for
you to see what it's pointing at.
Try this with bright stars like Vega or Sirius - they're the easiest :-)
*** Rotations and Revolutions... earth around the sun, moon around the
earth and how to figure out which direction they're rotating and
revolving...
The ecliptic plane is kept horizontal and the N-S axis of the earth is
kept tilted at 23.5 degrees as it moves around the sun - this explains
seasons in the northern and southern hemisphere.
To understand the lengths of day and night (and equinox and solstices)
your frame of reference is your horizontal plane (flat ground) - and you
are facing east. The pole star will then be on your left, at a height from the
ground equal to your latitude. Geometry of the equatorial plane and the
ecliptic plane and how the sun appears to move on the ecliptic, keeping
the earth's N-S axis vertical, will explain the length of day and night
according to the season.
various sundials plus the 'hand sundial'
-- morning : left hand
-- afternoon : right hand
Hold a pencil between your thumb and palm, with the pencil making an angle
equal to your latitude, with your palm. This aligns the pencil along the
N-S axis of the earth, and will always point at the pole star. The sun
should always be behind you...
Look at the shadow of the pencil on the tips of your 4 fingers and the
'joint-creases' on your little finger ( :-) I don't know what to call
them ! ) The numbering goes as 5,6,7,8 am on the tips of your fingers, and
then 9,10,11 on your little finger ( 11am being the base of the little
finger) and then 12 is the line on your palm that appears just below your
little finger. For the afternoon, use the right hand, and 12 noon is the
same line below the little finger, 1,2,3pm are on your little finger-
lines - and 4,5,6,7pm are the tips of the 4 fingers !
This is not very accurate - but gives a crude approximation...
*** Star Dial - telling the time
Use a dial and a pointer to get your sidereal time. A line drawn between
one end of Casseopeia and the 3rd star of the big dipper - passes through
the pole star and corresponds to Zero RA. So the angle between this line,
and the vertical - gives your location's RA which is your sidereal time.
( I think the numbering on the dial go as 0 on top and then from 0 to 23
anticlockwise ) --> This way, when the first two stars of the big dipper
are vertical, the dial will read 23.
There is a chart that has 3 columns - first one is the sidereal time
reading, the second is the local time, and the third is the time of the
year. You know your date, you find your sidereal time from the star dial,
and draw a line between the two on that chart. The place where it
intersects the middle column tells you teh time of day/night.
xplns
- This is for the various flavours of Linux
http://www.astroarts.co.jp/products/xplns/download.html
- This is something for Windows...
http://astrosoc.soc.ru.ac.za/archive/docs/skyglobe_course.html
- something else for windows...
http://www.eaaa.net/download.htm