6
REVISED GTO QUICK STAR DRIFT METHOD OF POLAR
ALIGNMENT
Using the Meridian Delay Feature and a Finderscope
Note the selection of suggested stars for this procedure in Appendix I
We suggest that you use these detailed instructions the first couple times you perform this method.
After you are comfortable with the procedure, a single-page Quick Reference Sheet is also provided
for convenience.
The●star-drift●method●is●the●favorite●way●that●astrophotographers●align●their●mounts.●After●all,●they●would●like●the●least●
amount●of●drift●possible●during●their●long●time●exposures.●An●Astro-Physics●GoTo●mount●makes●it●possible●to●simulate●this●
method●without●spending●a●long●time●waiting●for●drift●to●show●up.●It●is●also●easy●because●it●separates●the●two●adjustments●
of●altitude●and●azimuth●into●separate●operations.●
This●method●is●easiest●to●perform●using●a●finder●scope●with●a●cross-hair●eyepiece.●●●There●are●a●couple●good●reasons●
for●this:●First,●it●is●easy●to●adjust●a●finder●scope●to●make●it●perfectly●orthogonal●to●the●mount.●●●Orthogonality●is●not●a●
requirement●for●this●method,●but●it●does●make●the●process●much●easier.●●●Second,●the●wider●field●of●a●finder●makes●the●
first●iteration●or●two●much●easier●since●you●are●very●likely●to●already●have●the●star●of●choice●in●the●field●of●view.●●●●This●
is●especially●true●if●you●would●otherwise●be●using●a●long●focal●length●telescope●or●a●very●short●focal●length●crosshair●
eyepiece.●●●See●the●hints●in●#8●below.
NOTE: The diagrams below portray a hypothetical example to illustrate the concept.
●●●What●you●actually●
see●in●your●finder’s●crosshair●eyepiece●will●almost●certainly●be●considerably●different.●●●In●particular,●your●starting●point●will●
depend●on●whether●you●are●east●or●west●of●the●pole●in●azimuth,●and●whether●you●are●above●or●below●the●pole●in●altitude.●●●●
Also●note●that●the●number●references●in●each●diagram●(i.e.●2-b●or●5-c)●refer●to●the●corresponding●instruction●section●in●the●
text.
1.●
Follow one of the start-up alignment procedures from earlier in the manual (one complete cycle) to get close.
●●
We●have●found●this●method●particularly●effective●following●the●Daytime●Polar●Alignment●Routine,●for●aligning●without●a●
polar●scope.●●●This●is●especially●useful:●●1.)●in●the●southern●hemisphere,●2.)●with●the●3600GTO,●or●●3.)●in●a●situation●
where●the●pole●is●not●visible.●●●You●will●be●at●the●Main●Menu●when●you●finish●your●start-up●routine.●
2.●
Slew to a bright star that is within 1 hour of the meridian, either east or west, and as close to straight overhead
in the N-S direction as possible.
●●●●The●stars●listed●in●the●table●in●Appendix●I●will●provide●some●good●possibilities.●●●●●
See●the●instructions●that●accompany●the●table●on●how●to●select●stars●from●the●lists●for●more●details.●●●
a)●
Be sure that your telescope is on the west
side of the mount when pointing to a star in
the east and vice versa.
●●●●Choose●a●bright●
star●that●is●right●at●or●just●south●of●your●zenith●if●
you●are●in●the●northern●hemisphere,●and●right●
at●or●just●north●of●your●zenith●if●you●are●down●
under.●●●●This●is●to●protect●your●instrument●from●
hitting●the●pier●when●you●flip●sides.
b)●
Use the direction buttons to line up the
crosshairs of your finderscope’s eyepiece
●
with●the●movement●of●the●axes●by●turning●the●
finderscope’s●eyepiece●until●N-S●movements●
parallel●one●hair●and●E-W●movements●parallel●
the●cross●hair.
c)●
Center the star
●on●the●crosshairs●●using●the●N-S-E-W●buttons
d)●
Press the RA/DEC/REV button; then select the #9=Re-calibrate
●option●(from●the●RA/DEC/REV●Menu).●●You●will●
hear●a●beep●letting●you●know●you●successfully●re-calibrated.
3.●
In the RA/DEC/REV menu look at the Meridian Delay selection.
●If●the●star●is●in●the●west,●advance●the●meridian●by●
1●hour●so●that●the●display●shows●Meridian<1W>.●Use●the●PREV<●and●NEXT>●buttons●to●advance●the●hour●and●also●
change●the●direction●to●either●W●or●E●(pressing●PREV<●multiple●times●will●display●the●hours●in●the●east).●If●the●star●is●in●
the●east,●enter●<1E>.●(You●can●verify●if●the●star●is●in●the●east●by●comparing●its●RA●value●to●the●current●“z”●or●LST●value.●●●
A●larger●RA●value●indicates●it●is●in●the●east;●a●smaller●RA●value●indicates●it●is●in●the●west.)●●●Press●MENU●a●couple●times●
to●return●all●the●way●back●to●the●Objects●Menu.●(Don’t●stop●at●your●star.●●Go●all●the●way●to●the●Objects●Menu.)
