Sunday, October 28, 2007

Comet 17P/Holmes

David Hudgins sent out an email on Wednesday mentioning that an extremely faint comet, 17P/Holmes, had suddenly increased in brightness from around 17th magnitude (too faint for most amateur telescopes) to around 2.5 magnitudes -- about a million times brighter. The comet, in Perseus, could now be seen with the naked eye despite the nearly full moon. This is an extraordinary change.

I set up my 8-inch Orion XT Dob that evening and had a terrific view of the comet. I made the following sketch in my journal.

Here is a retouched version I made with Adobe Photoshop Elements 5.0. I inversed the image and made some color and level adjustments. I also replaced the original field ring with a better circle. Jeremy Perez has an excellent digitzing tutorial for adjusting eyepiece sketches on his Belt of Venus blog. And he has also co-authored a cool book published by Springer titled Astronomical Sketching.

Here is a plot I made of the same field using MegaStar. When I sketch objects I mark down all the brighter stars in the field -- say down to 9th magnitude. I try to capture any distinctive star patterns that will help me locate and orient the field in MegaStar. I also mark a few faint stars at the limit of averted vision. My key for this is F (faint but not hard to see), VF (very faint in averted), and VVF (challenging in averted -- only seen part of the time).

The MegaStar chart shows many more 11th magnitude stars than the few I included. I set the magnitude filter in MegaStar to 11.2 after determining that the effective limiting magnitude for this observation was just under 11. Fainter stars can be seen with an 8-inch scope, even from an urban sky. But the moon was nearly full. Also, this was a low power view. Fainter stars can be seen at higher magnification. See the detail at upper right of the journal entry, which was seen with a 7mm Nagler Type 6 at around 200x. All three 11 magnitude stars near the comet were easily visible.

Sunday, October 7, 2007

More About Cowbirds

Elly and I were watching the cowbirds yesterday morning, when she commented they must not be sexually dimorphic (which means that the sexes look different) because all the birds we saw looked the same. I said I thought they are dimorphic, so we checked Sibley which confirmed that they are. We took a closer look at the crown on the driveway. I counted over two dozen males and only three females.

I got out our Sibley Guide to Bird Life and Behavior, to read up on cowbirds, which are part of the icterid family. The icterids also include Orioles and Blackbirds among others. Sibley devotes a lot of space to cowbird brood parasitism -- the fact that they don't make their own nests but rely entirely on laying their eggs in the nests of other birds. I didn't read the entire entry. Later in the day I called Mark McKellar at the Backyard Bird Center to ask him about why we saw so many male cowbirds and so few females. Mark is our "ultimate" birding authority when we can't figure out a birding question. A lot of other people's too. Anyway, Mark explained that male and female cowbirds migrate separately. The males generally migrate first, followed later by the females. I guess that is common among the icterids.

I took the above picture of a gorgeous buckeye butterfly yesterday afternoon. It was feeding on some beautiful purple flowers in our neighbor's front yard. I'm going to have to ask what sort of flowers they are. Along with the buckeye, dozens and dozens of bees were collecting pollen from them.

I also met my sister Karen at Browne's Irish Market for lunch yesterday. We have lived a few blocks from Browne's (a Kansas City landmark and institution) for 19 years and I had never visited it! They have all sorts of Irish-related merchandise and a deli. I had a BLT on whole wheat that was absolutely delicious. Karen and I have decided to make it our hangout when she visits KC.

She gave me a novel she had bought (The Art Thief by Noah Charney), saying it was one of the worst books she had ever started reading, she was furious with herself for wasting money on it, and just wanted it out of the house. I opened to the first page and read "It was almost as if she were waiting, hanging there, in the painted darkness" and burst out laughing. "Karen, the opening sentence is an indefinite-it construction!" (Sort of a major no-no in the writing business.) I promised to dispose of it properly. I plan to take it to Propsero's Books and ask them to burn it. Prospero's made international news (the London Times sent a reporter) when they started burning books customers wouldn't buy and charities wouldn't even take for free. You can read more about that on their website. They are only a few blocks from our neighborhood, too.

Here is one more picture of those purple flowers.

Friday, October 5, 2007

50 Million Cowbirds

Okay, well maybe five dozen is more like it, but that is still a lot of cowbirds in our backyard. Over the last month their numbers have been climbing at our morning junk bird convention. I took these pictures this morning.

Elly thinks it must have been a good year for them. I guess they leave their eggs in the nests of other birds. Ornery critters. I wonder what factors make them more or less successful in any given year? Or why they are congregating around here this year? We've noticed that the numbers of particular birds rise and fall. A few years ago we had about 6 dozen house finches with us throughout the winter. The last couple of winters, though, there have been only half a dozen or so.

They certainly have the mourning doves outnumbered these days.