Page 46 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

+20º
NORTH +15º
Moving scope north or south changes declination Moving scope east or west +10º

changes right ascension

EAST ORION WEST +5º
Line of right ascension 0º

Celestial equator Line of declination

SOUTH
–5º

7h 10m 7h 6h 50m 6h 40m 6h 30m 6h 20m 6h 10m 6h 5h 50m 5h 40m 5h 30m 5h 20m 5h 10m 5h 4h 50m 4h 40m 4h 30m 4h 20m 4h 10m 4h

EQUATORIAL

MOUNTS

PART 3 HOW THE MOUNT MOVES

HOW TO MOVE AN In the fi rst two parts of this guide to latitude is known as declination (or Dec.
EQUATORIAL equatorial amounts, we’ve looked at how to for short) and longitude is known as right
MOUNT’S AXES TO set up your mount so that it will do its job ascension (or simply RA).
Both of these systems work in exactly the
properly, making it easy to fi nd and follow
KEEP YOU ON TARGET objects out there in space. A star, planet or same way as they do for locations on Earth.
CHART BY PETE LAWRENCE, PAUL WHITFIELD X 5 the night sky, with the Earth at its centre ascension (longitude) lines run ‘up and down’,
Declination (latitude) lines run parallel to
nebula can be found by using its co-ordinates
the equator from east to west, while right
on the great imaginary sphere projected onto
– the celestial sphere.
from north to south. Every single object in
As we mentioned previously, fi nding a
the night sky has Dec. and RA co-ordinates,
just as every location on earth has a latitude
galaxy in this way is almost identical to the
and a longitude. By using the Dec. and RA
way you locate places on Earth using latitude
and longitude; you just imagine the grid
setting circles on your equatorial mount, you
difference is that on the celestial sphere,
sky with just these two fi gures.
46 skyatnightmagazine.com 2012 projected onto the starry realm. The only can point your scope to fi nd anything in the