Page 47 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

WHAT TO USE

WHEN THE TUBE BUMPS THE TRIPOD

To keep track of your quarry as it moves from east to west, you might need to do a ‘meridian fl ip’

Declination axis

Right
ascension
axis

STEP 1 If your telescope’s tube bumps into STEP 2 Next, rotate the declination axis so STEP 3 You’re ready to begin observing
the tripod as you’re tracking an object moving that the telescope tube is pointing at the again. A meridian fl ip is often needed on
with the night sky, rotate the telescope tube object again. You can use the declination axis objects that are at their highest in the sky, so
by 180º in right ascension. setting circle to get back to the original spot. the tube is pointing straight up.

Assuming you’ve already polar aligned fi nderscope – to zero in on the target. Now The beauty of the equatorial mount now
your scope as detailed in Part 2, the fi rst step take a look at the RA setting circle dial. If this comes into play: as you gaze in wonderment
to fi nding that galaxy is to make sure your is your fi rst setup, it might not be reading the at your galaxy, you only need to adjust the
right ascension setting circle is set correctly. exact RA position that you looked up earlier. RA axis with its slow-motion control to keep
For this you’ll need the RA co-ordinates of If this is the case, don’t worry: simply it in your eyepiece as it moves from east
an easily found bright star, like Vega in the rotate the RA setting circle’s dial until the to west across the sky. And if you fi nd the
constellation of Lyra (see page 10). Vega’s pointer reads the correct co-ordinate. The occasional twiddling of the RA slow-motion
co-ordinates can be found from a star atlas, Dec. setting circle’s dial is fi xed in the correct control a little tedious, you can get a motor to
or a planetarium program like Stellarium. position, so you needn’t fret about this going attach to this axis, which will do the tracking
out of alignment. Now you can use the setting for you automatically. As for the declination
HEAD FOR VEGA circles to fi nd your galaxy, simply by moving axis, you don’t have to touch that or its slow-
Loosen the locks on both the RA and Dec. the axes so that the setting circles match the motion control until you want to look at a
axes and move the scope until it is more galaxy’s Dec. and RA co-ordinates. You can different object. Then you just look up the co-
or less visually aligned with the star, then use this method to locate objects that are ordinates of your next quarry, and move the
use the slow-motion controls – and your below naked eye visibility, too. Dec. axis and the RA axis until the setting
circle dials give the right readings.
So, a well-handled equatorial mount is
pretty much the perfect solution to hassle-
free stargazing. Well, almost; there is one
thing it can’t do, and that’s track an object
all the way across the sky. There will come a
point when the bottom of the scope’s tube will
bump into the tripod leg, especially if it’s a
long tube. Luckily, there’s an easy way around
this called a ‘meridian fl ip’ – see above.
Hopefully, if you’ve read all three parts
of this article, you’ve now got a bit more
confi dence when it comes to using an
equatorial mount. Astronomers have been
Adjusting the declination axis moves your Adjusting the right ascension axis moves fi xing their telescopes on this kind of mount
telescope in a north-south direction your telescope in an east-west direction for almost two centuries; now you can too.
skyatnightmagazine.com 2012 47