Monday, August 13, 2012

Hunting Himalia - Part Two

For Part One, click here.


My observing circle is filled with people with far more observing experience than I, people who have been amateur astronomers since adolescence, people who have forgotten more about astronomy than I’ll ever know. Q: What can I possibly bring to the table? A: Enthusiasm!

When I read or hear about an object that intrigues me, and I then find out it’s accessible to amateurs, suddenly I have to see it. I’m on fire to see it—and make sure others see it too. I do like to instigate.

I’ll mention the object casually to observing pals, talk it up, drop hints. In the process, I’ll sometimes discover that, amazingly, few to none of the seasoned veterans have seen it. That’s all I need to hear to put that object firmly in my crosshairs. In the case of Himalia, even the ΓΌber-observers of my club hadn’t seen it. Here was an irresistible challenge: pursue an object even they hadn’t seen!

I knew the Fall 2011-Spring 2012 apparition of Jupiter would be ripe for a Himalia quest. Jupiter was rising around 10 p.m. in September, and so would be high enough to begin Himalia hunting around midnight. It’s always a plus when you don’t have to stay up bleary-eyed until 4 a.m. to acquire your target. Another big plus would be the warm late-September night; no clothing layers required. Yup, this was gonna be great.


Final Prep Step #1: Assemble the Equipment

With the promise of good weather and clear skies as the appointed evening approached, the mate decided to retrieve his 24-inch reflector from storage, where it had been safely stowed since our move to the mesa. Although that may sound like mosquito hunting with an elephant gun, all that glass can help tremendously when trying to recover a 14.8 magnitude speck.


Since it’s not a tracking telescope—a motorized telescope that keeps acquired targets in the field of view by compensating for Earth’s rotation—we decided to place it on an equatorial platform, which turns a non-tracking scope into a tracking one. Although the platform is heavy and must be manually re-set every half hour or so, not having to worry about constantly nudging the scope to keep your target centered is a huge plus when you need all your concentration just to spot it.

Equipment Checklist
  • 24-inch f3.9 home-made reflector (aka “The Cannon”)
  • Osypowski equatorial platform
  • 13mm Nagler eyepiece
  • 4.5-inch Starblast with 24mm eyepiece (used as a finder scope on the 24-inch)
  • Ladder
  • Jellybeans
"The Cannon"

Equatorial Platform
  

Final Prep Step #2: Assemble the Experts

With the mate—a more seasoned observer—at my side, I had substantially increased my odds of success. While setting up at our astronomy club’s observing site, we pooled resources by reeling in Kevin, a very accomplished observer who also had Himalia on his life list and was keen to try for it. Kevin was familiar with the motions of Jupiter and its moons, which proved extremely valuable in our shared quest.

  
The Main Event

At the appointed hour, the mate re-set the equatorial platform to get a full 30 minutes of accurate tracking, and then aligned his telescope using his NGC-MAX (a computer controller that aids in locating objects). I read off the RA and DEC coordinates for Himalia from my ephemeris (see Part One) and he tapped them into the NGC-MAX. He inserted a 13mm eyepiece in the focuser, as we had determined that the field of view produced would be a good match to the field shown in the DSS image.

After pushing the cannon-like scope to the coordinates, he climbed the ladder to the eyepiece clutching the piece of paper with the DSS star field image. After rotating the paper once to the right, the image matched what was in the eyepiece. A few bright stars in a triangle pattern and a three-star arc within the target field helped. Piece of pie!

He then set out comparing the DSS image to the eyepiece view, star by star. Finally, he was left with one star in the center of the field of view that was not represented on the DSS image. It had to be Himalia, didn’t it?

I climbed the ladder next, and using the DSS image, was easily able to tick off the brighter stars in the field, including the triangle. I made my way incrementally to each dimmer star in the field, but was only able to see the top star of the three-star arc. I couldn’t see the two dimmer stars below it. I waited to let more light integrate on my retinas. And then using averted vision, I saw the central speck that wasn’t on the DSS image. The mate confirmed that it was dimmer than the top arc star but brighter than the two lower arc stars, which explained why I could see Himalia, but not the lower arc stars.

Himalia was seen at tip of arrow


We huddled to confer. It couldn’t be just another star in the field that was too dim to be represented on the DSS image, because it was brighter than the two lower arc stars, which were on the image. It had to be Himalia, didn’t it?

Kevin mounted the ladder next. He easily spotted the “interloper” star in the field. We discussed whether we could see it move that night. Observed movement against the background stars would be verification that it was no star. Based on how much the RA & DEC coordinates on my ephemeris changed over time, it seemed likely. In fact, Kevin predicted that, if we waited about an hour, we would be able to see motion. With his knowledge of the current motions of Jupiter & Company, he also predicted in which direction we would see the Himalia candidate move.

I kept thinking: can it really be this easy? Rick Scott’s article (see Part One) had made this target sound so daunting. As it turned out, what we had—that the author didn’t—was aperture, 24 inches compared to his 10 inches. It made all the difference.

We waited about an hour to see if the suspected moon moved against the background stars. Sure enough, it had shifted westward, moving in the direction Kevin had predicted. Eureka! Himalia was ours!

I was only able to see Himalia with averted vision, that is, by using my peripheral vision and looking at a spot in the black sky right above it, rather than directly at it. My two observing partners were able to see it with direct vision, the second time they looked at it. This is because  1) Himalia was then a little higher in the sky and less obscured by Earth’s atmosphere, and  2) their eyes are annoyingly better than mine. Given Himalia’s faintness, I was suitably impressed with Rick Scott’s accomplishment, spotting it with far less aperture. How did he do it?

Although it was exciting to observe such a tiny fleck of reflected light, one of the best views of the night, for me, was when I looked at Himalia and couldn’t see it. Let me explain.

Starblast (little blue scope) riding piggyback as a finder scope


We were using a 4.5-inch Starblast, a nice little telescope in its own right, as a finder scope (targeting tool), riding piggyback on the 24-inch scope and aligned with it. The view through the finder provided a much wider field of view and much less magnification than the big scope. I could therefore see Jupiter and all four Galilean moons, with a lot of black space around them. Himalia was centered in the big scope—and staying centered because it was tracking. So when I looked through the finder, I knew that Himalia, although I couldn’t see it with such low magnification, was dead center in the field of view. That allowed me to see the big picture, where Himalia was in relation to its host planet.

I knew Himalia was considered a “far-ranging” moon; indeed, most moons in Jupiter’s large harem have far-ranging orbits. Himalia floats through space about seven million miles from Jupiter. Compare that to the orbit of Earth’s Moon, a mere quarter of a million miles from its parent planet. The view through the finder confirmed Himalia’s lonely orbit: it was more than one degree from Jupiter, far from the mother ship and its four famous satellites. A degree in the sky is two times the width of a Full Moon as observed from Earth.


  

Four other seasoned observers on the field that night—Dave, Bob, Ed, and Vance—came over for their first look at Himalia. This is what I call “giving back”: for all the fabulous views of remarkable objects offered to me over the years and for the unfailing generosity of the amateur astronomy community.

Hunting Himalia was team astronomy at its best, and we seven could now say we had “been to Himalia”!

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