Levenhuk Skyline 90x900 EQ Telescope: EN

Focusing

Slowly rotate the focus knobs under the focuser one way or the other until the image in the eyepiece is

sharp. The image usually has to be nely refocused over time, due to small variations caused by tempera-

ture changes, exures, etc. This often happens with short focal ratio telescopes, particularly when they

haven’t yet reached outside temperature. Refocusing is almost always necessary when you change an eye-

piece, add or remove a Barlow lens.

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Polar adjustment

In order for your telescope to track objects in the sky you have to align your mount. This means tilting the

head over so that it points to the North (or South) celestial pole. For people in the Northern Hemisphere

this is rather easy as the bright star Polaris is very near the North Celestial Pole. For casual observing, rough

polar alignment is adequate. Make sure your equatorial mount is leveled and the nderscope is aligned with

the telescope before beginning.

Look up your latitude on a map, road maps are good for this purpose. Now look at the side of your mount

head, there you will see a scale running from 0 to 90°. Loosen the mount latch slightly rotating the lock

handle counterclockwise. A thumbscrew located underneath the mount head pushes the latch plate, thus

changing the angle. Turn the screw until the pointer on the latitude scale is set at the latitude of your

observation site.

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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 ne adjustments in

azimuth if needed. For more accurate alignment, look through the nderscope and center the Polaris on the

crosshairs using the azimuth and latitude adjustment knobs.

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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 eld.

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

eld 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 eld. 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 rst nd a

star in your eld 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 eld 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 nd objects in the sky.

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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.

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A problem for many beginners is recognizing that a polar-aligned, equatorial mount acts like an alt-azi-

muth 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.