Get cash back on your astronomy and other purchases: Ebates Coupons and Cash Back

Sunday, April 20, 2014

Star hopping with Cartes du Ciel

The other night the clouds finally cleared up, so I was able to get the AD10 out and make my first attempt at star hopping.  Earlier in the day I figured Auriga would be the best area of the sky to pursue since it would still be above the neighbor's tree and away from the lights.

Using Cartes du Ciel, I had plotted out some maps with finder and eyepiece circles.  If you haven't checked out this program, it's quite nice (and free!)  You can set up your own finder circles by going to the Setup->Display menu option and clicking the Finder Circles tab.  You'll need to figure out the field of view (FOV) of your finder and eyepieces.  Through some observation, I found that Orion's belt spanned from the center of the crosshairs in my 9x50 finder right to the edge of the field.  That tells me my finder has about a 5.5 degree field, so I entered 330 in Cartes du Ciel.  The input is in minutes (5.5 * 60 = 330).

Through calculation, I figured out my 30mm eyepiece has a 96 minute FOV.  How did I arrive at this?
My scope has a 1250mm focal length and the eyepiece is 30mm, so magnification is 1250/30 = 41.7x.
The specs of the eyepiece say it has a 68 degree apparent FOV (AFOV).  True field of view (TFOV) is AFOV / magnification, so 68/41.7 = 1.6 degree TFOV.
Convert to minutes, 1.6 * 60 = 96 minute AFOV.

Using the same calculations, I arrived at 48.57 minutes for my 30mm with 2x Barlow, 22.45 minutes for my 9mm, and 11.22 minutes for my 9mm with 2x Barlow.

In Cartes du Ciel, I only enabled circles for the finder and 30mm with and without Barlow.  If all of them are enabled, the chart gets too crowded.

I set the program's time to 8pm and located Auriga.  I know that I can see Capella easily with my naked eye and can barely make out Al Anz and Hoedus Li (I got these names from Cartes du Ciel).  All three stars barely fit in the finder circle, so I started by positioning the screen so all three were in the circle and zoomed in so the circle field the screen.  I printed this first chart and labeled it #1.


Next, I shifted the view so Hoedus Li was at the bottom edge of my finder view and printed chart #2.  That puts several promiment stars near the center of the field of view.  Lambda Auriga (the Greek character lambda looks like an upside down y) is the southernmost one of the group.  I slid the view south, so lambda was at the rightmost edge of the view and printed chart #3.  This put M38 in the field of view, which is my first target of the night.  I centered on M38 and printed chart #4.  With M38 centered, M36 was also in the field, so I centered on M36 and printed chart #5.  On each of my charts, I also circled the items of interest so I wouldn't forget and drew lines showing which way I wanted to move when hopping.





















After dark, I set up and waited a few minutes for my eyes to adjust.  Hoedus Li was just above the branches of the neighbor's tree, so I positioned it in the bottom of the finder and started hopping according to my charts.  It took a couple of tries, but pretty soon I had the finder centered around where I thought M38 should be, although I couldn't see it in the finder (too much light pollution).  Looking in the scope with my 30mm eyepiece, I saw several stars bunched together at the edge of the field, so I shifted it over and was rewarded with a very nice open cluster.  I popped the 30mm into the 2x Barlow and M38 filled the field.  After admiring M38 for a while, I shifted my view to where I expected M36 to be and found it as well.

A very successful star hopping experience!

No comments:

Post a Comment