16_english, Sing the setting circles – Sky-Watcher EQ3GOTO MOUNT User Manual

Page 16

The RA setting circle is numbered from 1 to 24 in 10

minute increments. The example above shows the mount

is set to the RA coordinates of 8h 20m. The lower scale

marked 1 to 12 is the date scale. The upper scale is the

RA minute scale. Both of these can be ignored when

using the setting circle scale for finding objects.

Vega is the brightest star in the

Summer Triangle, which consists of

Deneb (Cygnus), Altair(Aquila) and

Vega (Lyra). In this image Vega is at

the top. In the sky when facing east

it will be the highest of the three

stars with Deneb to its left (north)

and Altair to its lower right (south).

Fig.n

Fig.o

Now it is time to learn what those numbered dials are for!

The dials are called setting circles and they can be used

to help you find objects in the sky simply by dialing in a

set of coordinates.
All objects in the sky have assigned coordinates labeled

Right Ascension (RA for short) and Declination (Dec for

short). The RA axis follows east/west movement of the

sky and is the primary axis. By periodically rotating the RA

axis you are able to follow the apparent motion of the sky

and keep objects centered in your eyepiece. This is called

tracking.
The Dec axis is for north/south positions. It is primarily

used for finding objects, not for tracking them. It is normal,

however, to make occasional adjustments to the Dec axis

as well. The better your polar alignment, the fewer Dec

adjustments you will need to make.

sing the Setting Circles

10 8

Altair

Vega

Deneb

First you need to calibrate the RA axis (Fig.n). To do this align your telescope to an object with known

coordinates and then rotate the RA setting circle to show those coordinates. Leave the setscrew unlocked at this

point. Your Dec scale is factory set and does not need to be calibrated in this way. Once you are aimed at the

known object the Dec scale should have the correct coordinate reading.
Now as you rotate the scope in RA and Dec, the setting circle values change. So, to find a specific object, you

simply turn both the axes until the designated coordinates line up with the pointers on the respective scales.

After finding the object, centre it in your eyepiece, then lock the RA set screw securely. This will prevent the RA

setting from incrementing as the telescope tracks the object. You only want the RA setting circle to rotate with the

mount when you are locating objects, not when tracking them.
Let’s do an example. During summer nights the star Vega shines brightly overhead (Fig.0). Vega is easy to find

because it is so much brighter than any other stars in its general vicinity. It’s easiest to find Vega by spotting the

Summer Triangle. This is a trio of bright stars in the eastern sky consisting of Deneb (Cygnus), Altair (Aquila) and

Vega (Lyra). Vega is the westernmost of the three stars. It will be highest overhead of the three for northern

observers. Find Vega and centre it in your eyepiece.