Download Instructions for the HALO Setting Circle/Leveling Base

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Instructions for the HALO Setting Circle/Leveling Base
Please read all instructions before beginning to familiarize yourself with the process!
In addition to the HALO and the included Alti-Gauge, you will also need a planetarium program or app on your laptop
computer, tablet, or smartphone, in order to get the current Altitude and Azimuth coordinates of the object you want
to observe. Some of the most popular programs/apps are Stellarium, SkySafari, Starwalk, and SkEye.
Attach the curved steel baseplate to your Dobsonian base:
Tools needed to mount baseplate
Measuring tape
Pencil
Angle Square (or a piece of rectangular paper)
The curved steel baseplate provided with your HALO comes
with pressure sensitive adhesive on the back side. You will
need to peel the liner off and stick the baseplate to the outside edge of
your Dobsonian base. The baseplate should be installed on the same
side of your base as the focuser on your telescope (normally the right
side of the base, as seen from the FRONT of the scope/base).
Accurate positioning of the baseplate
Using a measuring tape, determine the midpoint of the right vertical
side. Make a small pencil mark at the midpoint (or use tape if you
would prefer not to make a pencil mark).
Place a carpenter’s square (or the 90 degree edge of a piece of
paper) against the right vertical base member, at your midpoint
mark. Use the straight edge to make another mark at the outside
edge of the base, in line with your midpoint mark.
Peel the liner off the back of the baseplate, and carefully apply
the baseplate to the edge of the laminate on your Dobsonian
base, aligning the small center-mark on the edge of the
baseplate with your pencil mark. Once the baseplate is properly
positioned, press down hard to make the bond permanent. At
this point, you can attach the magnetic adjustable pointer to the
baseplate.
Setting up your HALO at the observing site:
1. Hold the HALO flat in front of you with the built-in
bubble level/compass pointing away from you. Rotate
your body until the compass points north, giving the
compass time to settle. Keep in mind that nearby
metallic objects (including unseen objects
underground) could affect the accuracy of the
compass, so try to keep the HALO away from metallic
objects during positioning.
2. Once you are oriented towards magnetic north, set the
HALO on the ground in this same position. You’ll notice
that the 90° mark (under the compass) is actually on the north side of the HALO, and the 0° mark will be on
the west side. This may seem counterintuitive at first, but the HALO is designed so that the pointer is always
under the focuser/eyepiece while giving you the proper azimuth readings.
3. Level the Halo by adjusting the leveling feet up or down until the bubble is centered in the built-in bubble
level/compass. Your Halo should now be level and pointed towards magnetic north. Keep in mind that these
are APPROXIMATE alignments, and will be further refined after installing your telescope in the Dobsonian
base.
4. Carefully set your Dobsonian base in the HALO, making sure that the feet on the bottom of your Dobsonian
base are set inside the cut-outs on the inside perimeter of the Halo.
5. Place the magnetic pointer at the mid-point of the curved steel baseplate on the Dobsonian base.
6. Install your telescope onto its Dobsonian base.
7. Install the Alti-Gauge on your Dobsonian’s optical tube (the
bottom of the gauge has strong magnets and will stick to any
telescope with a steel tube). The position of the gauge is
critical to achieving accurate results. With the optical tube in
the horizontal position, set the gauge at the very TOP of the
tube’s diameter (i.e. the “highest” point on the horizontal
tube). And the face of the gauge must be perpendicular or
“square” to the long axis of the tube as seen here.
8. Now rotate the telescope so that it is pointing approximately north. Install a low power/wide angle eyepiece
in the focuser. A 30mm eyepiece is generally a good choice for this.
9. At this point you should attempt to center the North star (Polaris) in the eyepiece of your telescope. If Polaris
is hidden behind an obstruction, try to find some other identifiable star in the northern portion of the sky,
such as one of the stars in the big dipper or one of the stars in the constellation Cassiopeia. The closer the
chosen star is to Polaris, the less it will move in your eyepiece, which will make calibrating the HALO easier and
more accurate. Once you have Polaris (or your other reference star) centered in your eyepiece, slide the
magnetic pointer on your Dobsonian base to the azimuth of your reference star. If your scope is centered on
Polaris, the pointer may be several degrees away from 0°. This is not a defect of your telescope or the HALO,
but is due primarily to your local Magnetic Declination. Also, Polaris is not located EXACTLY at the Celestial
pole, so its azimuth is not always exactly 0° (although it is always within about 2° of true north). So when you
use Polaris to set your HALO’s pointer, set the pointer to the ACTUAL azimuth of Polaris according to your
planetarium software at the time you are calibrating.
Understanding Magnetic Declination
Magnetic declination is simply the angular difference between magnetic north and true north. A compass points to
magnetic north (reacting to the earth’s magnetic fields), while true north points to the North Pole, which is at the
Earth’s axis of rotation. Magnetic north changes with location and time, so if you want to know the magnetic
declination at your observing site, you will need to look it up on the internet. You do not absolutely need to know
your local magnetic declination to use your HALO, but it can help you place the HALO in an orientation closer to true
north before placing your Dobsonian base in the HALO, which means you won’t have to move the pointer so far to
calibrate it.
Understanding and using the degree marks on your HALO
The HALO has half-degree markings to help you accurately set your telescope to your target object’s azimuth. But
planetarium programs don’t display azimuth or altitude in half-degrees; they display them in degrees, minutes, and
seconds. For example, a given star at a given time might have an azimuth coordinate of 176° 45’ 15”. You can ignore
the seconds (15” in this example) because that is too small a measurement to use on a setting circle. But you should
definitely take the minutes (45’ in this example) into account, and try to set your HALO pointer as close to the minutes
coordinate as possible. There are 60 minutes in each full degree, and 45 minutes is 3/4 (75%) of 60 minutes. So for
the example coordinate above, you should set the HALO pointer at roughly three quarters of the way between the
degree marks for 176° and 177° (or about halfway between 177° and the half-degree mark right before it).