Free Public Programs Home | Driftway Observatory Home | Give You Joy Home

« Previous individual entry || Next individual entry »

Doubles? No trouble!

I observed several double stars last night with various telescopes in the process of developing an exercise – an experience - focused on doubles for the public programs.

This particular exercise is designed to help them start to develop several observing skills, but the real goal is to get my guests thinking about star color and asking what it means. It’s very difficult to see color in stars and also very subjective. There are some objective differences in our physiology that makes for different reports as well, not to mention the differences introduced by instrument used and conditions. Still, there is some general agreement about color usually, and, of course, there’s the scientific evidence of the star’s spectrum which sometimes- but not always – matches the observer’s perception.

Simply put it’s easier to see star colors when you have two contrasting stars right next to one another, thus the focus of this exercise on double stars. My challenge on this particular night is to make sure my plans are realistic in terms of the stars being looked at, the telescopes being used, and choices of eyepieces. I also want to get a better handle on the observing skills needed to see if my expectations for them are realistic. I’ve chosen six multiple stars to work with suitable for late fall/early winter, and I want to point some of the scopes at some of the stars myself – otherwise they’ll never get through the lesson in the time allotted – but I also want them to find one or more of the stars using charts on their own.

Here’s my list of stars: Albireo, Almach, Polaris, Gamma Aries, and Iota and Eta Cassiopeia. And here’s what I found about each star.(You can find some wonderful color drawings of several, if not all, of these double stars on tis web site. )

Albireo – This is one of the easiest to find and certainly the easiest to split, since it’s right at the head of Cygnus and there’s a lot of separation and the “blue and gold” colors are widely reported. I’m going to have them use the ShortTube 80 mm refractor on this one, with an Alt-Az mount and 25mm and 10mm eyepieces. They should be able to find it fairly easily and they’ll also gain experience using different eyepieces –one to find it (low power) and one to view it (higher power) .

Almach – this too is a bright star, easy to find, and generally reported as blue and yellow. Some like it better than Albireo, but I still have an emotional attachment to Albireo since it still sticks in my mind from viewing it as a teenager. But I want them to learn the basic outline of Andromeda in this lesson and Almach figures prominently in that task. I used the lovely little 4.5-inch Orion Dob and found it instantly in the 25mm (36X), although the 10mm eyepiece (91X) is needed for a good solid split.

Polaris – I think this is a good one for the LX200, but on this night I haven’t dragged that scope out. I’ll have them find it, since pointing to the North Star certainly should be within their skill levels and with the alt-az mount and manual slow motion controls (the computer is dead on this scope) they should have no problem. Of course, once someone points it towards it, it will stay in view – no tracking needed – so they’ll have plenty of time to play with different eyepieces. I checked this using the 6-inch Skywatcher refractor and found I could split it easily using the 25mm Plossl with a 2X Barlow – that’s around 96X in this telescope. They may be able to split it with just the 25mm in the 8-inch LX200 – that would give them 80X. But it might be a better experience to have them start with the 40mm (50x) , then use the Barlow to double it. (One of the observing skills to pick up during this process is to see that the Barlow doubles the power while maintaining the eye relief of the lower-powered eyepiece.)

Gamma Aries – I really love this little pair of “cat’s eyes.” They are so perfectly matched in brightness and color and easy to find and split. While there’s no color contrast here, this is a wonderful example of a double star and good one for the beginner. But I won’t have them find this because Aries is not one of the constellations they know. Nor is it high on my list of constellations worth learning. Instead I’ll point the ETX90 at it and simply let them fool with eyepieces. In this case I found that a 25mm eyepiece (50X) will split it, but it’s much better using the 13mm Plossl (95X). Heck, I was even able to split this one with a 40mm eyepice (31X) I was using t find it, which is a testimony not to the huge gap between the stars, but how evenly they are matched in brightness so one doesn’t drown out the other. The 13 mm eyepiece has relatively little eye relief, so it will serve as a good example of the difference between using a Barlow and using certain high-powered eyepieces. (In this case this is one of the very early Televue Plossls.)

Iota Cassiopea – This is a triple, but I don’t think I’ll tell them that in advance. I’ll see if they can “discover” it. While this star is fairly easy to find – and a good one to demonstrate how best to use the Telrad reflex finder with its lighted circles for star hopping – I think I’ll find it with the LX90 and let it track it. They can focus on observing and changing eyepieces. Besides, while I split it with the 6-inch, I needed 240X and seeing conditions might not allow that much power. I’ll have to see how it does with the LX90 at either 180X, 200X, or 222X. I know they’ll be able to split it in two – the question will be how much power does it take on that scope – and with the sky conditions of the moment – to see the third component. Taking the need to find it out of their hands, they’ll be able to focus on the issues of power and seeing and thus increase those observing skills

Eta Cassiopeia – this is an easy star-hop to find, so I’ll have them use the 6-inch refractor which includes both the Telrad sight and a decent 6X30 optical finder. Here the observing skills learned will be in the finding of the double, though it will be very interesting to see what they report in terms of color.

Speaking of reporting, they will have a simplified observing form where they will draw each double, showing separation, estimated position angle, and relative brightness, then write down their impressions of color. I found this an easy split in the 6-inch, especially at 96X – the 25mm plus 2X Barlow.

Notice anything missing? Yep – the 15-inch Obsession. I tested it the other night on M103. What I found was that cluster has five bright stars of varying hues. So I’ll lock the 15-inch on M103 and have them try to identify the star colors. The bonus is that the next observing session will focus on open clusters – assuming no interference from the moon – and this will make a good transitional object. It will give a final focus on star color and a first example of an open star cluster, Oh, and to make things even better this particular cluster – at least in the 15-inch – looks like a little Christmas tree with a bright star at the top and colored bulbs. How seasonal can you get? Wonder if any of them will see it that way without being told? (yes, I know the “real” cvhristmas Tree Cluster is over in Monocerosos and it is better – but hey, we see what we see and this is what I see when I look at M103 with this scope ;-)

Ok – back to last night – I was able to test all this, fool around with various eyepiece combinations, and then get the scopes packaed away as the clouds started to roll in – we’re due for a little snow this morning, which is Thanksgiving. I also got a look at the best meteor I’ve seen this fall, if not all year – I would put this at about magnitude –2 and I wish there had been others out there with me because it moved slowly enough from Andromeda to Cygnus and was so bright and large that I would have had plenty of time to call the attention of others to it. (For the record, that came at about 6:25 pm EST in case anyone else nearby reading this might have been looking ;-)

Oh – and the real bottom line? On the surface I’m doing lesson development, but what I’m really doing is getting in about 90 minutes of wonderful observing time and while the objects observed aren’t all new to me, I learn with every experience. The main lesson I came away with from this night’s session is that I know some stuff that I don’t know how to teach. In fact, I’m not sure it’s teachable – but it is learnable through experience. What was this. exactly? Well, it’s difficult to put into words, but I know these stars – especially the new ones – were easier for me to find then they will be for a newcomer. Looking in a finder and recognizing exactly which of the stars in the wide field of view is your target, is one of those experiential skills that builds with repetition and variety. The more things you find on your own, the easier it gets. So there’s no golden road to this knowledge, no easy shortcuts – but you can sure enjoy yourself traveling it anyway and hey, why not – it’s covered with star dust!

Posted by Greg Stone at November 24, 2005 02:45 AM Comments? Please email me: gstone@umassd.edu

Clear Sky Clock | Awe, awareness, and astronomy | Introduction to astronomy | Astronomy links | Driftway Observatory Home | Give You Joy Home