Page 44 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

Aligned on the north celestial
pole, an equatorial mount
makes it easy to track stars
as they move from east
to west through the night

North
celestial pole Towards Polaris

Star rises

Star sets

EQUATORIAL

MOUNTS

PART 2 ALIGNING

THE SECOND PART In Part 1, we looked at setting up an It’s a notional spot that denotes the point
OF OUR GUIDE TO equatorial mount so it would be a solid and at which our planet’s axis of rotation meets
celestial sphere, that imaginary ball with the
stable platform for holding your telescope.
EQUATORIAL Now we’re going to explain how to make Earth at its centre, onto whose inner surface
STEVE MARSH, PAUL WHITFIELD X 4 YOU HOW TO objects as they move with the sky as the only appears to rotate; it’s actually Earth
the mount follow, or track, stars and other
all the stars are projected. The sky, in fact,
MOUNTS SHOWS
that’s rotating, once every 24 hours. But
night hours tick by.
ALIGN ONE SO
To do this properly, the equatorial mount
since we’re observing from the surface of
the spinning Earth, it looks as though it’s the
has to be ‘polar aligned’; its right ascension
THAT IT CAN TRACK
(RA) or polar axis must be lined up so that it
THE STARS
points at the north celestial pole. This is the
Since the sky rotates (or appears to)
point that the sky appears to rotate around. night sky that is rotating around us.
around the north celestial pole, the mount
44 skyatnightmagazine.com 2012