The Astronomy Nexus is a personal website covering all sorts of topics on astronomy and other interests.

Endeavour: additional large star catalog

The Endeavour application now has a large subset of the fourth US Naval Observatory CCD Astrograph Catalog (UCAC4). The subset contains over 30 million stars to magnitude +15.0.

Here's an example of the difference. This is the M13 area using the Tycho-2 catalog:

And this is the M13 area with the UCAC-4 subset:


I've just completed a monster rewrite of the old Distant Worlds star charting application. It now has a bunch of new features:

Long time coming

Yes, I know this site has been pretty dead lately. Interstate moves can do that. Fortunately, that's been over for a while, giving me some time to make updates.

The Star Mapper has gotten a big -- and long overdue -- update. New features include:

  • When you hover over a star to get its information, the information appears next to the star instead of in the upper right. The star itself gets highlighted as well.


I am hosting some of the larger downloads on this site on GitHub now. The most current version of the HYG database will always be posted there. Any publicly available code relevant to the site will go there as well.

Lunar eclipse shots

It was clear for just long enough here in Colorado to get a good view of the eclipse. I got a number of decent shots with just a compact camera (Panasonic Lumix FZ-28, most at the max zoom level of 18x). As I've told a friend once, since the albedo of the Moon is similar to that of fresh asphalt, getting the right exposure settings for the full Moon is about as hard as getting them for a sunlit street. With an eclipse going on, it's a little tougher, but aggressive exposure bracketing solves many ills, and is very simple with almost any digital camera.

Here's one of my favorite shots (click to embiggen):

More images below the break:

Site updates

The Distant Worlds Star Mapper has gotten a rewrite. There isn't a whole lot visible on the outside, but charts should get created a bit faster, especially if you have a lot of extra details (like constellation lines) turned on.

In Science News!

Science News has published one of my images from this site. The October 23 issue has an article about Gliese 581, discussing the potentially Earthlike planet discovered recently in its habitable zone. The image is a slight modification of the large chart in this post, showing the Sun among other stars as seen from Gliese 581.

Visualizing the Universe, Part V: Gliese 581

The faint star Gliese 581 has been getting a lot of press lately: it's the first star known to have a fairly small planet in its habitable zone, or the region of space where liquid water can exist. Although we've found a few other planets in (or close to) probable habitable zones, they've been much larger. The recent discovery appears to be only a few times more massive than the Earth, rather than hundreds or even thousands of times more massive, as many exoplanets are.

What kind of star is Gliese 581? For one thing, it's not very much like the Sun. It's much dimmer. In fact, even though it's about as far away as stars like Fomalhaut and Altair, it's much too dim to be seen with the naked eye. Here's where it is in our sky. It's in Libra, not too far from the bright stars of Scorpius:

After the break, we're going to take a trip to Gliese 581 and look around.

Visualizing the Universe, part IV: Time to Get a Move On

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.

Visualizing the Universe, Part III: The closest star

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:


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