- Simulated experiments such as microscope simulators or virtual chemistry laboratories
- Distributed computing projects, which are applications that do not require any user effort other than downloading and installation
- Aplications with specific purposes to actively aid amateur science practice, such as planetariums
I have a bit more experience with distributed computing projects, having been a volunteer on Seti@home - back in its first year (1999-2000). Only the second large-scale project of this type, the grandiose aim is to discover radio signals broadcast by alien civilisations. All the user has to do is download and install the application, which then runs when the computer is idling as per a glorified screensaver. In this particular case, the Seti@home signal-processing software is able to search for extra-terrestrial transmissions that might be only 10% the strength of earlier surveys, using data collected by the giant Arecibo radio telescope. The application has proved to be remarkably successful, having been downloaded to over 3 million personal computers.
But if this project is a bit blue sky for you, there are plenty of others with more down-to-earth objectives. For example, Folding@home and Rosetta@home are fantastic opportunities for all of us non-professionals to help molecular biologists studying protein folding in order to develop cures for diseases such as HIV, Alzheimer's, and Huntington's. So far, the research has generated over a hundred research papers, but the complexity of the subject means there's plenty of room for additional computers to get involved for many years to come.
The third class of software supplies the user with the same sort of functionality as commercially-available applications, but in many cases surpasses them in terms of capabilities and quantity of data. These tend to congregate into a few classes or themes, suitable for usage amongst amateurs of variable capability and commitment.
One popular category is planetarium applications such as Stellarium, which has plenty of features for city-bound (i.e. restricted vision) enthusiasts such as myself. It even includes a night vision mode, red-tinted so as to keep the observer's eye adjusted to the darkness, although unfortunately my telescope camera software doesn't have an equivalent and as I cannot reduce the laptop screen brightness until after I've achieved focus, I'm left stumbling and squinting until my eyes readjust. Stellarium seems reasonably accurate with regards to stars and planets but I've never managed to check if the satellite trajectories confirm to reality.
For anyone lucky enough to live in a non-light polluted environment there are more sophisticated free applications, such as Cartes du Ciel-SkyChart which allows you to create printable charts as well as remotely control telescope drives. If you are really an expert at the telescope then C2A (Computer Aided Astronomy) is the bee's knees in planetarium software, even able to simulate natural light pollution during the lunar cycle and allowing you to create your own object catalogues!
As an aside, what gets me with these applications is how they calculate the positioning of celestial objects from any location on Earth, at any time, in any direction, and at varied focal lengths. After all, there is a well-known issue with calculating the gravitational interactions of more than two celestial objects known as the n-body problem. So how do the more sophisticated planetarium applications work out positioning for small objects such as asteroids? I used to have enough issues writing basic gravity and momentum effects in ActionScript when building games in Adobe Flash! All I can say is that these programmers appear like mathematics geniuses compared to someone of my limited ability.
Back to the astronomy freeware. Once I've aligned my telescope courtesy of Stellarium and recorded either video or a sequence of stills using the QHY5v planetary camera (wonder if they'll give me any freebies for plugging their hardware?) I need to intensively process the raw material to bring out the details. For this image processing I use another free application called RegiStax which again astonishes me as to the genius of the programmers, not to mention their generosity. Being a regular user of some extremely complex (and expensive) commercial image editing applications since the late 1990s, I undertook a little research into how such software actually works. All I can say is that unless you are interested in Perlin noise functions (seeded random number generators), stochastic patterns, Gaussian distribution and Smallest Univalue Segment Assimilating Nucleus (SUSAN) algorithms - nice! - you might just want to accept that these applications are built by programmers who, as with the planetarium software builders mentioned above, have advanced mathematics skills beyond the comprehension of most of us.
So in case you weren't aware, the World Wide Web provides far more to the amateur scientist or student than just a virtual encyclopaedia: thanks to the freeware Samaritans you can now do everything from finding the position of millions of astronomical objects to examining electron microscope images of lunar dust. It’s like having Christmas every day of the year!