Discovery Spark 769 EQ Guia Del Usuario página 15

the pointer on the latitude scale is set at the latitude of your observation site (fig. 10).
Loosen the Dec. lock knob and rotate the telescope tube until the pointer on the setting circle reads 90°. Retighten the
Dec. lock knob. Loosen the azimuth lock knob and move the mount so that the R.A. axis points roughly at Polaris. Use
the two azimuth adjustment knobs above the "N" to make fine adjustments in azimuth if needed. For more accurate
alignment, look through the finderscope and center the Polaris on the crosshairs using the azimuth and latitude
adjustment knobs (fig. 11).
After a while you will notice your target drifting slowly North or South depending on the direction of the pole relative to
Polaris. To keep the target in the center of the view, turn only the R.A. slow-motion control.
After your telescope is polar aligned, no further adjustments in the azimuth and latitude of the mount should be made in
the observing session, nor should you move the tripod. Only movements in R.A. and DEC axis should be made in order to
keep an object in the field. In the Southern Hemisphere you must align the mount to the SCP by locating its position with
star patterns, without the convenience of a nearby bright star. The closest star is the faint 5.5-mag. Sigma Octantis which
is about one degree away. Two sets of pointers which help to locate the SCP are α and β Crucis (in the Southern Cross)
and a pointer running at a right angle to a line connecting α and β Centauri.
Tracking celestial objects
When observing through a telescope, astronomical objects appear to move slowly through the telescope's field of view.
When the mount is correctly polar aligned, you only need to turn the R.A. slow-motion control to follow or track objects as
they move through the field. A R.A. motor drive can be added to automatically track celestial objects by counteracting the
rotation of Earth. If the object is too faint you may want to use setting circles on an equatorial mount. Setting circles allow
you to locate celestial objects whose celestial coordinates have been determined from star charts.
The telescope's R.A. setting circle is scaled in hours, from 1 to 24, with small lines in between representing 10 minute
increments. The upper set of numbers applies to observations in the Northern Hemisphere, while the numbers below
them apply to observations in the Southern Hemisphere.
Setting (calibrating) the R.A. setting circle: in order to set your Right Ascension circle you must first find a star in your
field of view with known coordinates. A good one would be the 0.0 magnitude star Vega in the Constellation Lyra. From a
star chart we know the R.A. coordinate of Vega is 18h 36m.
Loosen the R.A. and DEC. lock knobs on the mount and adjust the telescope so that Vega is centered in the field of view
of the eyepiece. Tighten the R.A. and DEC. lock knobs to lock the mount in place. Now rotate the R.A. setting circle until it
reads 18h36m. You are now ready to use the setting circles to find objects in the sky (fig. 12).
A German Equatorial mount has an adjustment, sometimes called a wedge, which tilts the mount's polar axis so that
it points at the appropriate Celestial Pole (NCP or SCP). Once the mount has been polar aligned, it needs to be rotated
around the polar axis only to keep an object centered. Do not reposition the mount base or change the latitude setting.
The mount has already been correctly aligned for your geographical location (i.e. Latitude), and all remaining telescope
pointing is done by rotating the telescope tube around the polar (R.A.) and declination axes (fig. 13).
A problem for many beginners is recognizing that a polar-aligned, equatorial mount acts like an alt-azimuth mount which
has been aligned to a celestial pole. The wedge tilts the mount to an angle equal to the observer's Latitude, and therefore
it swivels around a plane which is parallel to the celestial (and Earth's) equator. This is now its "horizon"; but remember
that part of the new horizon is usually blocked by Earth. This new "azimuth" motion is called Right Ascension (R.A.). In
addition, the mount swivels North (+) and South (–) from the Celestial Equator towards the celestial poles. This plus or
minus "altitude" from the celestial equator is called Declination (Dec.).
Now, consider pointing the telescope to the western or eastern horizon. If the counterweight is pointing North, the
telescope can be swiveled from one horizon to the other around the Dec. axis in an arc that passes through the NCP (any
Dec. arc will pass through the NCP if the mount is polar-aligned). It can be seen then that if the optical tube needs to be
pointed at an object north or south of this arc, it has to be also rotated around the R.A. axis. Pointing in any direction other
than due North requires a combination of R.A. and Dec. positions.
Telescopes with long focal lengths often have a "blind spot" when pointing near the zenith, because the eyepiece-end
of the optical tube bumps into the mount's legs. To avoid this, the tube can be very carefully slipped up inside the ring
clamps. This can be done safely because the tube is pointing almost vertically, and therefore moving it does not cause a
Dec. balance problem. It is very important to move the tube back to the Dec. balanced position before observing other
sky areas.
Something which can also be a problem is that the optical tube often rotates so that the eyepiece, finderscope and the
focusing knobs are in less convenient positions. The diagonal mirror can be rotated to adjust the eyepiece. However, to
adjust the positions of the finderscope and focusing knobs, loosen the tube rings holding the telescope tube and gently
rotate it. Do this when you are going to observe an area for while, as it is inconvenient to repeat every time you briefly go
to a new area.
Finally, there are a few things to consider to ensure that you are comfortable during the viewing session. First is setting
the height of the mount above the ground by adjusting the tripod legs. You must consider the height that you want
your eyepiece to be, and if possible plan on sitting on a comfortable chair or stool. Very long optical tubes need to be
mounted higher or you will end up crouching or lying on the ground when looking at objects near the zenith. However, a
short optical tube can be mounted lower so that there is less movement due to vibration sources, such as wind. This is
something that should be decided before going through the effort of polar aligning the mount.
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