HOW TO MAKE GUIDE 8 PREPOINT CHARTS FOR ASTEROID OR LUNAR OCCULTATIONS

BY Scotty Degenhardt

The first thing you need to do if you haven't already is download the updated version of Guide 8 that activates this animation feature. The brief directions are here:

http://www.projectpluto.com/update8.htm

How to use the update files: To get the update and the features listed below, download one of the following three files and unZIP it in your Guide directory.

32-bit (Win95/98/NT/XP) update (GUIDE8.ZIP) (about 885 KBytes)

16-bit (Win3.1) update (GUIDE8A.ZIP) (about 585 KBytes)

32-bit DOS software (DOSGUIDE.ZIP) (about 805 KBytes)

Next, once you decide on an event (I will use my 20080912 (9) Metis event as an example) you do the following:

• Open Guide 8
• Under the SETTINGS tab change the location to the longitude, latitude, and estimated elevation of the planed observing location.
• Change the Guide time to the predicted time of the event for the above longitude and latitude.
• Then I click the GO TO tab and say GO TO ASTEROID and enter the asteroid number. This then centers the screen on the target. As a redundant error check here I look to see that the yellow asteroid X is actually over the predicted target star.

• Verify this by right clicking on the target star and make sure the star ID matches the predictions.

• Now that you have right clicked on the target star and clicked OK you can activate Guide to make the animation track. To do this now hit ALT-J keys at the same time. A window will pop up that asks for the "Number of test flags". Enter 1.

• Now go to the ANIMATION tab and click on "Add a trail".
• I have attached a screen shot of the configuration I prefer. This adds 1 minute tick marks backwards in time for however many minutes you specify. In the attached example it would create a trail in the sky with tick marks every 1 minute backwards in time for 150 minutes, and it will label the time every 5 minutes.

• Then it is up to you to create charts with whatever magnification you need for your field of view. I usually like to go to the DISPLAY tab and "Create CCD frame" and make a rectangle representing the FOV of my camera so that it gives me an idea of what I can expect to see.

I usually print out three types of charts:

1. A wide field of view (FOV) at Level 3 = 45 degree FOV so that I can locate the target area amongst the sea of constellations in the sky. I also use this wide chart to star hop from the brightest star near the part of the track that is close to the UT time I need to point to.

2. I then print a complete series of overlapping charts from event time backwards to start of deployment time that have enough magnification that I am comfortable that I can locate the time with enough resolution to assure the target will be centered. For my mighty minis I am fortunate to have an almost 3.5 degree FOV, so I print Level 4 charts (20 degree FOV) at one hour intervals. With my 80mm short tube refractors from Orion using the Owl focal reducer I have about 1.5 degree FOV and print out overlapping Level 5 charts (10 degree FOV) in 20 minute increments. To step through forwards and backwards in time to print your charts click on the ANIMATION tab, then ANIMATION DIALOGUE and the following interface will open. Make sure to check the Horizon box in the Locked on section. You can click on the single black arrows to step forward or backwards in time. I have configured this to step in a custom step of 20 minute increments (to set this up click on the box that is labeled “20 min” and enter your custom time step size):

3. I print out a target star finder chart for identifying the target at reduction time, or for last minute prepointing.

So now I can arrive anytime at any location in my deployment path, identify the UT time on the chart that shows me where I need to point, and I can star hop to that area. Then at precisely the event time I entered in Guide 8 to generate the track the target star will be centered at the event time I used. So here’s some of the rules of deployment I live by:

o Never ever ever ever go straight to the target star, ALWAYS prepoint!

o 9 times out of 10 the target star is faint and/or located in an awkward star hopping point in the sky. Prepointing allows you to pick the most convenient time to aim the scope and to pick the brightest star near the most recognizable asterism (saves an INCREDIBLE amount of time, blood, sweat, tears, hair follicles, adds years to you life, takes years off your wife…. Yada yada you get the picture).

o Starting at the target star instead of prepointing means that you have to stay on the target star, i.e. your polar aligning better be good (lotsa deployment time there), your motor drive better not have errors (lotsa $ there), and your batteries better last, even in the cold… (lotsa prayers there)!

o Prepointing uses THE most accurate drive available to man… the Earth’s rotation.

o LiMovie reduction with a prepointed target star drifting through at a steady rate is a breeze to accomplish using the “Drift” Tracking Method.

Scotty Degenhardt

scottyd@charter.net