Hi all!
I was at the 2009 Border Stargaze where I was asked to write in about the Astrolabe I built.
Basically the Astrolabe converts the co-ordinates of RA-DEC to Alt-Az..this is done by setting the co-oindinates of an object to the DEC arc first, TIME circle second and the RA wheel third..all these are illuminated by red LED's...then by moving the Altitude Arc around the Azimuth Circle you align the red marker LED from the DEC arc to the Altitude arc..this will then give you the Altitude and Azimuth of the object.
The Time wheel is shown recessed into the RA circle. This to allow the adjustment required to set the local time/star alignment for the night's viewing.
The RA wheel is shown with the time incriments (00hrs to 2359 hrs) around the circumference.
The (fixed) RA indicator is attached to the DEC arc. The DEC arc shows the position of the obect in degrees (note the red marker on top of the DEC indicator) and the position in RA in Hours and Minutes.
The Azimuth circle (which is also part of the base) is also the horizon.
The Altitude Arc sits and rotates around the Azimuth circle.
How does it works?
Setting up for local time.
Ok, you first must have your Dob complete with setting circles, level, and set up facing true North/South. Also have the Longitude/Latitude of the location and the local time.
Set the Dec axis support to show the angle in degrees applicable to the Latitude of your location (against the horizon on the base).. ie if your location is 37 degrees...adjust the South Dec Axis to 37 degrees above the (base) horizon.
Find a bright star to do the star alignment, have it's RA and DEC figures on hand. Find the star and tranfer the Alt-Az numbers to the Astrolabe. Now adust the RA/DEC on the astrolabe to the Alt-Az and ensure they align. Now set the time wheel against the (illuminated) guide to the hour/min current local time. You are now set for the night' viewing.
All you have to do to find an object is to follow the directions in the first paragraph. It should locate the object within the finderscope's FOV
The astrolabe was built mainly out of 7mm 3-ply with some of the broader section made from layers of 3-ply glued and clamped for a minimum of 3 days before cutting/shaping.
Dimentions.
Azimuth circle. ID 582mm OD 718mm x 7mm
Altitude Arc. ID 582mm OD 646mm x 7mm
Base, from Horizontal line on Azimuth circle to (A) the top of the DEC axis support arc 244mm. (B) bottom of base 314mm.
Dec axis support arc holder (attached to the bottom of base) 2 x 21mm W x 77mm H x 582mm L.
Dec axis support arc. ID 552mm OD 642mm x 42mm
Dec axis support bracket. 300mm x 421mm x 14mm
Dec axis arc. 2 x ID 469mm OD 532mm x 7mm at 270 degrees
Dec axis spacer blocks. 5 x 31mm x 15mm
Ra wheel. Dia 458.5mm circumference 1440mm (1mm = 1 minute) x 14mm
Time ring (recessed). ID 351mm OD 445mm x 3mm
Axis shaft. 21mmx x 21mm x 720mm.
Other blocks and fittings were made from plywood, plastic, etc
Power supply to the Dec arc, RA Wheel and Red marker was via a copper wire glued to the outer circumference of the Dec Arc.
LED's powered by 2x 1.5 volt AA batteries in switched battery holders
You can changes the type of materials to suit and the illumination of the setting numbers (someone suggested using optic fibres)..
It's a challange for anyone with plenty of spare time or an excuse to buy new tools and such...
Cheers!
Norm Matyson.
The Spacegate Astrolabe
