I've added a few new features to the site.

Distant Worlds Star Mapper: There are several new enhancements. Major ones include:

a: Chart settings

1. Show R.A. and dec. lines: For locations near the Earth (within 32 light years), you can toggle a grid of equatorial (right ascension and declination) coordinate lines on or off.
2. Show constellation boundaries: Also for locations near the Earth, you can toggle constellation boundaries on or off. These are the official boundaries you see in star atlases.
3. Abbreviate Bayer/Flamsteed designations: Choosing this option will remove the constellation abbreviation from any label that has a Bayer (Greek) letter or a Flamsteed number. For example, α Dra would become simply α and 61 Cyg would become 61. This is best used with constellation boundaries, so it's clear which constellation the abbreviated labels apply to.
4. Show all Bayer designations: Choosing this option will override the usual magnitude display limit and force all stars on the chart with a Bayer or Flamsteed label to display it, regardless of magnitude. The magnitude display limit will still apply to stars with a different designation, such as a proper name or a catalog number such as Hipparcos or Gliese numbers.

   Selecting all 4 of the options above will produce a view very similar to a chart out of a major star atlas.

5. Identify Sunlike stars: This will place a small yellow cross around every star that meets the primary criteria for the Encyclopedia of Suns: spectral type V, luminosity 0.1 to 3.0 times solar, and no obvious spectral peculiarities. As usual, hover your mouse pointer over the star to get additional details.

Additional features after the break:

Expected tonight: a lunar eclipse. Actually seen: your basic, unlovely nebular occultation, at least from my back yard. In fact, for much of the night it wasn't obvious that anything unusual was going on, except through the occasional break in the clouds. Fortunately, one member of my local astro club, Brian Kimball, did get a nice picture through some light clouds.

(h/t Bad Astronomer)

17th to 3rd magnitude in less than 24 hours!

I've made a few more changes to the Distant Worlds Star Mapper. The big ones are:

• Most stars now show single Greek letters instead of the English names for the letters (e.g. α instead of "Alpha", and π instead of "Pi"). This should make the chart labels less cluttered.
• The pop-up details for individual stars show more information, including proper name, catalog designations, spectral tyes, and absolute magnitudes.
• The charts now include the standard constellation boundaries. These only appear for locations reasonably close to the Sun (within about 15 light years), because at large distances the Earthly constellation names and boundaries are pretty meaningless.

I've updated the software behind the site overnight. One big change: you don't need to register to post or view comments. However, every comment field has a captcha (one of those distorted-text-in-an-image thingies) as an anti-spam defense.

Oh yeah, I know -- the current theme could use some work. The old one I had isn't compatible with the site update. I'll probably have a somewhat nicer-looking version up in the next week or so.

I've got some pesky spammers here, doing the old "stick a bunch of spam in older posts" stunt, and since it's been pretty quiet the last couple of months, I've turned off commenting for the near future. It'll probably come back after a general site upgrade in the next few weeks...

I have updated the HYG Database. It now includes the complete Hipparcos catalog (the old version had only stars to magnitude +9.0), and it includes velocity information where it's available.

More details are on the main HYG Database page linked above.

April in the northern hemisphere means galaxies -- lots of 'em. But what do you do if you live in the city, can't get to a dark-sky site easily, and it's close to full moon?

How about a few stars, for a change? Recently, I took a look at several bright double stars, for a change of pace from my usual choices of planets and deep-sky objects. More details below.

I have made another significant update to the Distant Worlds Star Mapper. It now draws much more realistic star images. There are some sample screen shots after the break:

In the various discussions about the dynamics of the potentially habitable planet around Gliese 581, the issue of tide-locking comes up. How do we know that a planet like this may face this problem? It's closer to the parent star, of course, but the star is a lot less massive as well.

It turns out it's not too hard to estimate the tidal forces, at least at the order-of-magnitude level, for a clone of Earth put around another star. More details below.