Tuesday, May 21, 2013

Returning For Another Look!

Last night, with only a night or so left of moonless dark time to examine Comet PanSTARRS (C/2011 L4) again before the full Moon wipes it out, even though it was a "school night", I had to go up and take another look.  Since we are 2 days closer to the orbital plane crossing on the 27th, with the tail look any different?  Actually, I misspoke in my last post, it is not a "solar spike" even though it is pointing generally towards the sun, rather, it is called an anti-tail, because it is on the side opposite the main cometary body from the normal tail.  This is common when we observe the comet as we cross the plane of its orbit - perspective allows us to see dust released long ago appearing to jut out from the coma apparently the wrong direction from the head. In this case, the "real" tail is the puny spray of material going the other direction from the bright "ray"  It is that ray that is the anti-tail...

Anyway, last evening I napped part of the night away, awakening about 1am to head up to Mount Lemmon's Geology Vista again.  The bright Moon was still high in the western sky as I drove about an hour to the site.  Instead of setting up the AP1200 mount and the 14", this time, anticipating a long anti-tail, I just set up a tripod and tracking platform to enable me to use normal or telephoto camera lenses without a lot of setup.  Starting out with my 70-200 Canon F/2.8 zoom, I set it to 90mm so I could keep Polaris and Gamma Cepheus in the frame as reference to measure the tail.  I took frames for about 40 minutes, taking the in-camera darks as well to reduce electronic noise.  The stack of the 8 three minute exposures is shown at left.  As in Sunday's post, Polaris is the bright star at left, and Errai is at right.  This image is rotated about 90 degrees from that image.  The two stars are about 13.5 degrees apart...  In this frame the tail extends over 7 degrees across the sky!  That is a big difference from the 4 degrees seen Sunday morning...  The ray was also barely spotted in my hand held binoculars.  Sorry for the gradients of brightness in the exposure - it is a combination of the edge of the Milky Way encroaching in the lower part of the field, and perhaps also some airglow or sky glow since this in only 30 degrees off the northern horizon...

Since anything worth doing is worth overdoing, I took another quick series of images with a Nikon 135mm telephoto. I only got in 3 frames before the growing twilight stopped me.  But the stack of frames, stretched ridiculously to get a better tail length is shown at right.  Here is is imagined to 8 degrees before it fades out...  Also visible is a couple satellite trails, and as above and in Sunday's post, the cluster to left is NGC 188.

I'm not sure I'll get another chance to see the comet this well with the full moon coming about the same time as orbital plane crossing, but it is sure fun to see this comet continue to put on a good show since it first came over our horizon in March!

Update:  I forgot to mention the tracking platform!  I got the Vixen Polarie tracker a couple months ago and you saw the first results in the time-lapse of Omega Centauri rising a few weeks ago.  The comet shot this morning was really the second time used for tracking and it worked very nicely.  Shown at left is a pic of it while shooting the above comet shot with the zoom lens.  Even though it has a weight limit of 3.5 pounds, I suspect I was pushing it with the big lens, but it seems to work fine.  You can see that when shooting very far North with a long lens like this and you can easily hit the body of the tracker, but that issue aside, I look forward to pushing it to longer exposures.  Shooting very close to Polaris with couple-minute exposures isn't pushing it much!  The 2 cables - the one on the camera goes to the intervalometer (exposure control), and the one for the tracking platform is an alternate power cord.  While it runs off 2 AA batteries, they only last a couple hours, so I power it through the mini-USB and a DC adaptor off a car battery...  Another thing to note - though the stars are out of focus, their color shows more clearly - and also seen between the end of the lens and edge of the frame is the fuzzy glow of the Andromeda Galaxy in the 20 second exposure!

No comments: