One of the first groups of stars to be recognized as an actual group -- not just a chance alignment -- is the Hyades in Taurus. This is the closest major open cluster to the Earth.

This is what the Hyades look like now. They are the roughly V-shaped cluster near the bright star Aldebaran. However, although Aldebaran rounds out the "V" nicely, it's not a member of the cluster.

The Hyades are close enough that we have reliable measurements of the distances of its member stars, and we also have good measurements of the velocities of the stars as well, so it's possible to calculate its motion over time.

In the previous post, I showed how a nearby star -- Barnard's Star -- appears to move against the sky over time. Barnard's Star is the second closest to the Sun. The closest star (actually, the closest three stars, all bound into one multiple star system) is the Alpha Centauri system, at 4.3 light years away, about 2/3 the distance to Barnard's Star.

Alpha Centauri consists of three stars, two bright stars (both broadly similar to the Sun, called Alpha Centauri A and Alpha Centauri B) in a close orbit, and a third, much farther out, that is currently slightly closer to the Sun the the other two. This star, a very dim, red star, is sometimes called Proxima Centauri to emphasize its closeness to the Sun; it is the closest star to the Sun we know of.

Unsurprisingly, Alpha Centauri was one of the first stars to have its parallax measured. Since Alpha Centauri is closer to the Sun than Barnard's Star, it shows a larger parallax shift every year. Additionally, it is moving through space more slowly, so its proper motion is quite a bit lower (despite being closer). As a result, the parallax effects are easier to see with Alpha Centauri:

As you may know, people first figured out distances to the stars by measuring parallax shifts coming from the Earth's orbit. You may be wondering, though: given how far away the stars are, just what does this look like?

The first reliable measurements didn't come until the 1830s, over two centuries after the invention of the telescope and long after the discovery of Uranus, all the Messier objects, many faint planetary satellites, and subtle planetary details. As you can imagine, it's a fairly small effect that's difficult to detect. How small? More below the break.

When I haven't had time (or clear skies) to go observing the actual universe, I've been working on some ways to explore the virtual universe. A few years ago, I designed a basic starchart maker for this site that contains the entire Hipparcos catalog, so it could be used to show the sky from any location within a few hundred light years from Earth. I also found a bunch of stellar velocity data a while back, so for the brighter stars at least, I've been able to run simulations in time as well as space.

By creating a whole bunch of related images, I've created a number of animations illustrating various ideas from amateur astronomy, astrophysics, and even human archaeology and history. I'll begin with a short trip (in time, at least) to the Hyades, the closest large open cluster to Earth, right below the break:

I haven't been posting a lot lately, largely because a lot of the really quick updates go on Facebook these days. Despite all this, I've been doing a reasonable amount of observing lately. A few weeks ago I had an especially clear night where I could just see the largest dust lane in M31, the Andromeda Galaxy, in the 12.5" scope from the back yard. That was the first time in quite a while I remember doing that.

Last night was nearly as good. It brought a typical November Front Range sky: dark (at least outside of downtown), clear, and really bad seeing (forget about planets or close doubles). Fortunately, with Jupiter pretty much gone and the late fall sky segueing into the brilliant skies of early winter, there was plenty to see even so. M35 and NGC 2158 were beautiful, as usual: NGC 2158 is dim, but rich, and a real treat in the 12.5" even from a suburban location. (Give it a try even in an 8" or 10" scope; you may be pleasantly surprised!) The Big 3 in Auriga (M36, M37, M38) showed up well, and M1, the Crab Nebula, was distinctly more than just a faint oval, even without a filter. I told people I was going to see a few stars, and maybe a galaxy or two, but I ended up seeing four: M31, the Andromeda Galaxy, its two bright satellite galaxies, and the dim but still distinct arc of the late-fall Milky Way passing nearly overhead.

Here's an image from three days ago (June 29, 2009). This is a full-sized crop of the original. I've tweaked the image slightly (grayscaling to improve chromatic aberration, and a touch of unsharp masking), but the effects are cosmetic; you can still see the same details in the original. The smallest craters clearly visible near the terminator are less than 10 km across: for example, you can see Hyginus A, at 8 km, and it's clearly more than just a couple of pixels). Not bad for a $250 optical tube and a $250 compact non-DSLR camera. It's definitely better than the first few views of the Moon I got through a $3000 telescope 25 years ago!

It's been a quiet few months thanks to rainy weather here in northern Colorado.

June 29 was the first day in 3 months that I got more than a quick look at the sky. As a result, it was more of a "summer showpiece" sort of night, full of big bright things like the 1st-quarter Moon, globulars like M13 and M3, and bright nebulas like M57 and M27.

Saturn, which I'd hoped to observe more in the spring, is finally on its way out; I saw it briefly, but only very low, with already poor seeing made worse by the altitude. I was hard pressed to see any moons besides Titan and Rhea, and no details on the disk itself.

I did get a few quick photos through the 100mm refractor:

Gliese 581 is back in the news, since it apparently has a medium-sized planet in its habitable zone. We have no way of knowing yet if it actually supports life, but if there are intelligent beings there, and they look in the general direction of Orion, they'll notice that one star is peculiarly radio-noisy:

Finally got a few shots in the 100mm scope (24x telescope magnification, time: 1/100 sec. at f/4.5, approximately 10x zoom on the camera itself). Each of these was reduced in size by a factor of 4, whereas last night's image is a 100% crop. The larger image scale does make it clearer just how thin the crescent really is. Unfortunately, Venus was very low and so the seeing was rather poor; the final image quality isn't a whole lot better than with just the camera itself.

Just a quickie tonight: Venus is approaching conjunction:

(FZ28, ISO 100, 1/100 sec, f/4.4, full optical zoom of 18x)

If I get a chance to slap the camera on the 100mm scope in the next few days, I will, but Venus is rapidly heading away from the evening sky.