Rascal or Rasalgethi - I got you this time!

February 19-20, 2008

Rasalgethi, which had fooled me a few morning ago, didn't escape this morning. This is one of those very rare red supergiants - one of just ten we can see with the naked eye, but even more rare than that might seem - forwhile there are about 6,0000 naked eye stars, red supergiants are one in a million - or fewer.. As it turned out, Rasalgethi was an easy target, but a difficult split. Still, well worth the effort - I don't think I've seen another star with such a vivid orange color. It's kissing cousin is a pale blue and using the 66mm I could only pick it out at 114X (Of course it would be easy in any larger scope.) Here's what happened on the 17th when I went looking for it, however:

At some point I looked at Alpha Herculis - Rasalgethi, but was surprised when I couldn't get a satisfactory split. It's a magnitude 3 and 5 star, separated by 4.6" of arc. That would be tough for the little scope, but I expect it to do it. When I reviewed the charts I discovered my problem. Memory had failed me. I was looking at Rasalhague, not Rasalgethi. Rasalhague is the brightest star in Ophiuchus and is very close to Rasalgethi. I was in the right region. I just assumed that since this was "alpha" Herculis, it would be the brightest of the two stars. It's really the fainter star - and since Rasalgethi actually is a variable that can go from 3.1 to 3.9, it might have been even fainter than normal. In any event, I discovered my error when I went in at 5:30 am - but by the time I got back out there was too much twilight to pick it out. it wasn't so light, however, that it would not have shown well in the scope - I just couldn't see enough stars with my naked eye to know where to point the scope.

Where to point this morning was obvious - or at least the pretender, Rasalhague , an almostperfect magnitude 2, was obvious, even with a just-shy-of- full moon low in the west washing out the sky. . Rasalhague - alpha Ophiuchus - makes it's own triangle with the "summer triangle" stars of Vega and Altair, forming a southern corner in counterpoint to the northern one marked by Deneb. Rasalgethi is significantly fainter than Rasalhague which makes me think it may be on the downside of its variability cycle. (It should be about one magnitude fainter, but seemed ot be more.) In the 8X45 binoculars there's a lovely S-curve cascade of 10 stars on its south flank, and a crazy rectangle of stars - with a few fainter ones nearby - to the north.

At 19X I was immediately struck by the vivid orange/red color. At 50X I thought I had a split, but the second star was to the west. It still looked that way at 80X. But at 114X I saw my mistake. The companion was nearly due east, judging from the drift. Actually, it's a bit south of east - PA 104 degrees. They're also about 400 light years away, and the red supergiant is about twice the diamter of the Earth's orbit! No wonder it's a heck of a lot brighter and bigger than our Sun! "Where is M13" puts the pair a bit above us on the plane of the galaxy and to our east on the galactic azimuth scale. To me this means that as I look at it, I'm starting to look "inward" - more toward's the center of our galaxy than the outer regions - but still a long way from it.

Sissy Haas describes this pair as "a brilliant orange-red and a vivid bluish turquoise." I'll accept that, though I really didn't catch much color inthe secondary. It was too faint in the ltitle scope and too overwhelmed by the primary. But it makes a nice challenge object for a 60mm.

Another challenge object for my morning session was 5 Serpentis. When I went looking for M5 the other morning I didn't realize that this 5th magnitude field star was double. But Sue French includes it in her "Celestial Sampler" collection. So I went back to find it. In 8X45 binoculars it was easy to see it, M5, and a three companions of roughly similar brightness that form and arc south of it. Even at the highest power - 114X - on the 66 I could still include M5 in the fov to the northwest. I put the companion a bit more west. This is also known as Struve 1930.

There's good color here. The report in Hass says "Fantastic view! A brilliant yellow star with a close little speck beside it, and globular M5 is at the edge of the field." Uh huh! Only the person making that report was using a 325-mm (13-inch) scope! That's a bit different from the view in the 66 in moonlight. Again, I split it - at least my drawing put the secondary in the right place. But I would agree with Smyth's description from another century - "Pale yellow;light gray." With doubles, much is in the eye of the beholder - and the glass eye they use to capture the star.

I closed out the morning in the twilight as I tried to pin down the correct star-hopping needed to easily find the globulars M10 and M12 in Ophiuchus. I made a mistake I know I've made before. I'm entranced by the pair of stars that are part of Serpens Caput and a very similar pair, just 12 degrees away, that are the hands of Ophiuchus. It's this second pair that are th start of the star hope to M12 and M10, but invariably I get locked onto the two in Serpends Caput. If you use the "hands," then move 8 degrees to third magnitude Han, then you have the base of the triangle. (This follows the same line set by the two pairs of stars - the hands and the pair in Serpens Caput.) M12 and 10 can be found at the head of this triangle,

M10 and 12 fit easily in the 8X45 binocular field and should fit int he field of the 66mm when my 24mm Hyperion arrives - that will give me around 16X and a 4 degree fov. This morning, however, I just wanted ot make sure I could find them. By the time I had done so the twilight made them all but invisible.

My evening session had not been as exciting, but I never have a bad time under the stars - just some are better than others. Last night the nearly full moon was rising and the skies were quite unsteady with some high clouds rushing by. Still, I was able to check on some favorites and become more familiar with them in the 66. These included Almach - very easy - and Mesarthim - very nice. I really like to pair Mesarthim and Mu Draco, but unfortunately they're not well placed for viewing at the same time - but what very similar stars! I looked for the companion of Polaris and thought I might have glimpsed it, but the moonlight was too much for finding the faint companion with the 66. I did drop in on Eta Cassiopeia. That's a good star for the beginner.

Tonight we have thelast total eclipse of the moon until december 2010 - weather is iffy, but we got a chance!