Tuesday, September 04, 2007

Star Hopping

I did some cool star hopping over the weekend. (No, sadly, I don’t mean I went dancing with Lindsay Lohan and Tara Reid.)

Star hopping is a method of finding your way around the sky. You start at some star or constellation or asterism you recognize and shift your field of view just a bit in one direction or another, to another star or constellation or asterism and then use that as a jumping off location for another shift. This is a typical way to find constellations you’ve never observed, or locate celestial objects that can’t be seen with the naked eye.

I was after this. Uranus. Uranus is in Aquarius. This month, Uranus is reasonably bright, at magnitude 5.9. That’s too dim to be seen with the naked eye from around Chicago, but Uranus should be visible in binoculars.

I’ve seen Mercury, Venus, Mars, Jupiter and Saturn. But Uranus, Neptune and Pluto are difficult targets.

I had three types of charts. I had the simple, full-sky charts published every month in Sky & Telescope and Astronomy magazines. I had detailed constellation charts and photographs in a great book, “Observing The Constellations,” by John Sanford. And I had a detailed ‘finder chart’ for Uranus published in the July, 2007, Sky & Telescope magazine.

I had a pair of 10x50 wide angle binoculars and my 2.4 inch refractor telescope.

It was a good news/bad news start: Uranus was relatively bright, as the outer planets go. And Uranus was very close to a ‘regular’ star that could be used to find its position, Phi Aquarii. However, Aquarius is one of those ‘low-in-the-south’ constellations that I had never observed. Also, Aquarius is a rather large constellation with no particularly bright stars or eye-catching asterisms.

It was a challenge, but I very much wanted to add the planet to my ‘life list’ of cool astronomical things I’ve seen.

My plan was very simple. I intended to start with Altair in Aquila. Altair is one of the brightest stars in the sky, part of the well-known ‘Summer Triangle’ with Vega and Deneb. From Altair I’d star hop slightly to the north to Delphinus, then shift east to Equuleus, and then straight east to the horizon to find the two brightest stars in Aquarius.

Altair is easy, and Aquila is a beautiful constellation. I found Delphinus easily. Gamma Delphini turned out to be a nice double star. I shifted to Equuleus with no trouble.

But the large star hop almost down to the horizon looking for Alpha and Beta Aquarii got me totally lost. I couldn’t make heads or tails out of the unfamiliar, very sparse star fields.

After about an hour of making trips from my backyard into my house to consult the full-sky charts, trying to single out little two-star sequences east of Equuleus, I decided to call that idea a failure and abandon it. I hated to do it, but when you’re lost it’s an obvious feeling in your gut. You’ve got to re-group.

So I studied the full-sky charts. I couldn’t make the star hops work approaching Aquarius from the zenith, so I decided to again start from Altair in Aquila, but instead of moving north to Delphinus I’d move straight south to Capricornus and then, from Capricornus, move east into Aquarius.

This was a tricky plan because Capricornus is also a low constellation I’d never before observed. But the two brightest stars of Capricornus seemed to be directly ‘under’ Aquila and they formed a reasonably distinct visual line.

And they did. Alpha and Beta Capricorni turned out to be visually striking in binoculars. Alpha Capricorni is a complicated multiple star system that’s very easy to see. Beta Capricorni is also a multiple star system, a telescopic double that’s very beautiful. The two components are very different. One is bright and white, the other is very dim and richly blue. It instantly became one of my favorite double stars.

From Alpha and Beta Capricorni, I star hopped east and, bingo, right to Mu and Epsilon Aquarii. From the vertical pair in Capricorn to a horizontal pair in Aquarius.

I had gotten to my target constellation. Now I had to work across the large constellation and then, darn it, farther down and closer to the horizon.

Mu and Epsilon Aquarii ‘point’ directly east, toward Beta Aquarii. Beta was reasonably bright and had Xi Aquarii just below it. Star hopping farther along the same line—Mu and Epsilon to Beta, then Beta to Alpha—was easy. Alpha Aquarii is a little three star sequence. Easy. Then there’s a short hop to the east to another three star sequence of Eta, Zeta and Gamma. Easy.

Then came a tricky part. Changing direction and moving down to the horizon.

Starting at the ‘left-most’ of the three stars, Eta Aquarii, I star hopped down to Lambda Aquarii. Seemed easy, the only reasonably bright star there. Then, the slightest shift east again got me to my destination [!], Phi Aquarii. For great confirmation of where I was, Phi is just above a tight, dim little three star grouping of Psi Aquarii 1, 2 and 3.

There was Phi Aquarii.

And there, EXACTLY as the detailed finder chart depicted it, was Uranus. A TINY little speck, but clear. I estimated it as half a degree away from Phi. I later checked. It was .3 degree away.

Through my telescope I couldn’t make out any disk. The highest power I use is 100x, and Uranus only resolves to a disk in at least 150x. But I could catch a hint of the aqua color. It may have been my imagination, but compared to the white of Phi Aquarii I believe I did see a green-blue tint to Uranus. Very cool.

One odd thing about star hopping is that even if the sequence is convoluted and difficult when you first do it, it becomes almost trivial to do it again.

I first observed Uranus Saturday evening and, later that night during commercials on the coverage of the US Open tennis tournament, I would grab my binoculars and go out to the backyard. The hops were fast and almost casual. Aquila to Capricorn to Aquarius, then across the constellation and down to Phi and Uranus.

Very cool.

Now I’ve seen it.

And there is a very big fringe benefit to finding Aquarius by going through Capricornus.

Neptune is in Capricornus. Neptune is next on my list.

However, while Uranus is magnitude 5.9, Neptune is MUCH dimmer, at magnitude 7.9. With Chicago skies and my optics, limiting magnitude is about 6.5, even on a good night. (When I was passing through Capricornus I checked out the area between Gamma Capricorni and Iota Capricorni. Neptune was there, between them and a degree or two north, but it was completely invisible to me. Even the field stars north of Gamma and Iota were invisible to me.)

But the outer giants move very slowly. Someday I’ll revisit Capricornus armed with something like a four inch refractor or an eight inch reflector. Or I’ll have my trusty binoculars and small refractor under really good skies where magnitude 7.9 will be just accessible. Then I’ll get Neptune.

Pluto will have to wait for me to get a piggy-back camera on a motorized drive.

Those things will be future posts.

But I’ve seen Uranus. That was my labor for the Labor Day weekend.

No comments: