Regular readers will know I'm hooked on astronomy programs, and we've reviewed quite a few in this International Year of Astronomy.

Today only, Carina Software, one of the premier publishers in the field, is giving away Mac, PC, and iPhone versions of their software for next to nothing. It's in honor of today's 40th anniversary of the Apollo 11 moon landing. On the iPhone, they are free, for the PC and Mac version, US$00.01. Note: Due to server overload the Mac and PC versions have been pulled for now. Here is the latest from the Carina website:

"First, our iPhone apps SkyVoyager and SkyGazer will continue to be free downloads from the iTunes app store all day long. No changes there!

At approximately 6:20 AM PDT this morning, we recieved a call from our web-hosting provider, bluehost.com, asking us to suspend the one-cent download offer for our Voyager and SkyGazer desktop software. Demand was so high that our automated serial-number generator, which emails serial numbers to customers, was sending out several thousand emails per hour - putting us in violation of our Terms of Service (TOS) agreement, and causing our email service to be suspended.

Our email has been restored, and we are catching up on our backlog of missing-serial-number emails manually. All customers who have purchased one-cent downloadable copies of SkyGazer and Voyager should recieve their serial numbers from us by the close of business today, Monday, July 20th, 2009.

After continued discussion with our web-hosting provider, it is unlikely that we will be able to continue providing our desktop software as one-cent downloads for the remainder of the day."

I'll focus on the iPhone offerings, in particular the more advanced SkyVoyager [App Store link]. Carina is also offering SkyGazer for free, which is slightly less advanced and has fewer features. I'd go for SkyVoyager at these prices.

OK, what can you do with this software? Well, just about anything to help you under the stars or to plan a night of observing. The software picks up your location from the GPS, and of course the date and time. It will display more than 300,000 stars and 30,000 deep sky objects (clusters, nebula, galaxies). You can see the night sky from any location on earth, and on any date you choose, even going back or forward centuries.

The software also contains NASA images, and work from other astrophotographers. Amazingly, if you have a computer controlled telescope, like a Meade, Celestron, and some other less well known brands, SkyVoyager will soon be able to wirelessly connect to it and steer to objects you select on the iPhone. You can get a complete list of supported scopes here. Note: To make the connection to your scope you'll need a piece of hardware, the Sky-Fi connector, not available until late September. Go to this page for more info.

There are a lot of iPhone/iPod touch astronomy apps out there. SkyVoyager is full featured, and has very deep and complete data bases, especially considering it is running on a phone or iPod touch. It updates comet positions, along with asteroid and satellite orbital data. It requires a WiFi network for these downloads.

The only thing I'd like to see is the ability to use the iPhone tilt/tip sensors and compass to match your sky chart to where it is pointing in the sky. That works really well on Pocket Universe, which I reviewed recently.

SkyVoyager normally sells for $14.95, so free is pretty compelling. Remember, it's today only. My fellow amateur astronomer colleague Steve Sande is reviewing the desktop versions of this powerful software today as well, so be sure to check out his thoughts. They are selling for only a penny, so it's truly an 'astronomical' saving.

Check these screen shots to see SkyVoyager in action:

The popular astronomy application Star Walk [App Store link] $4.99 US, has been updated with some new features. You can now see meteor showers on screen, as well as connect to Wikipedia for more information on objects you have selected on the detailed star map.

Star Walk is probably the prettiest of the astronomy guides available for the iPhone and iPod touch. It nicely renders the dense clouds of the Milky Way, and has good visual details of the planets. It also has photos of the Messier objects, which are galaxies, star clusters and nebula.

Star Walk is location aware, so it can match what you see in the sky to what is on screen using the GPS, or you can select from 10,000 cities. You can change your location to anywhere on earth, and manipulate time to look forward and backwards. You could see what the skies were like on your birthday, or even what they looked like centuries ago or centuries ahead.

Things that could be improved would be on screen buttons that take you to the N, S, E, and W skies. The way things work now, you have to drag the map around. When you look up a Wikipedia item, it throws you out of the program. It would be better to build in a web-kit browser so you don't have to launch Star Walk again.

The app has no built in documentation. The company web site has a short PDF with more information. Although the skies in Star Walk are beautiful, most of the skies we see in real life are not. It would be nice to be able to dim the faint stars down to more accurately mimic what we see in the real world.

Nature lovers and amateur astronomers will like this program. Some of the other options at the app store include Distant Suns, [link] at $5.99 US which I have reviewed previously, and Starmap [link] $11.99 US..

Here are some screen shots:

Starmap 1.1 (iTunes link) is a pocket-sized map of the sky that packs a great deal into a small package.

One thing that strikes you immediately is the challenge of incorporating all the options available into the iPhone's limited UI space. The button panel at the bottom of the screen is a 3D object that you can spin round to reveal more controls.

And you need them, because there's a lot Starmap can show you. Not just the stars and constellations, but also planets, expected meteors and "deep sky" objects like galaxies, clusters and nebulae.

Features I particularly like include: the night-vision mode (tints everything red to minimise your iPhone's own light pollution); the fact that, by default, only objects you're likely to see are shown in lists of stars and planets (you can toggle this on and off if you'd rather see a list of everything, below the horizon or not); and the general feeling that a great deal of thought has gone into building the app from the outset.

The main issue with Starmap, and it's one you'll notice pretty quickly, is speed. Right now, the app does not use any accelerated graphics and subsequently, the frame rate is 3 FPS. Dragging the night sky around beneath your finger is slow and the animation jagged; as a result, it can be a little frustrating to use. Consider this before you buy.

This is a known issue, though, and work is under way on a fully optimised 3D version running at 20 FPS. It might be released as soon as October, we're told.

That (and one or two crashes) aside, Starmap is a fantastic educational app and very good value for the price ($11.99). Existing users should hold out for future updates -- if they deliver what's promised, Starmap will be an almost irresistible purchase.

Oh, and one other thing would be nice: a function that controls the appalling British summer weather, and clears away the almost permanent cloud cover so that we actually have a remote chance of seeing some stars.

If you're a space freak, then you'll want to have a look at these three super-cool web apps for your iPhone or iPod Touch.

iSkyGaze tells you where to find various objects in the sky, depending on your location and the time of day. Sure, it'll show you where to look to see the sun and moon, but iSkyGaze also helps you spot things in deep space, like the Orion Nebula. This cool app even tells you how far away the object is, and the best time to see it.

Want to know how the sky looked on any given date from the past 10 years? Starry Night Mobile will tell you. It can also predict what your overhead view will be 10 years into the future. Just enter a zip code, landmark, or address and let the app do the calculating for you.

If checking out satellites or the International Space Station as it passes overhead is more your thing, then you'll love LookUp. Once you enter your location, the app will tell the precise time various orbiting objects will zoom by, complete with exact elevation stats and how much time you'll have to see it before it dips below the horizon.

Oh, and here's a bonus app for all you werewolves.