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Citizen science

Modern scientists deal with problems at a global scale, but a scientist or research lab may not have the resources to study the vast amount of observational data available.
In that case, scientists can embrace citizen science: the participation of the general public in scientific research.

Participatory monitoring

Many citizen science projects involve monitoring of plants, animals, and atmospheric conditions. People around the world can report what is happening near them to a central database, and scientists can develop a better idea of worldwide trends in ecology and the environment.
eBird is a citizen science project that encourages birdwatching enthusiasts to submit photos of birds near them. During their Global Big Day event on May 4, 2019, over 30,000 people from 171 countries reported 1.85 million bird sightings!
The eBird research team from Cornell uses the bird sightings data for trends and statistics, like mapping the abundance of a species over time. Here's an abundance simulation for the Ruby-Throated Hummingbird:
Animation of abundance simulation for Ruby-Throated Hummingbird. Left side shows a map of North America, with colored dots moving from Central America up to Canada, from January to December. Dots range in color from yellow to purple, indicating the relative abundance.
All of the eBird data is openly available, so any researcher, conservationist, or birder can use the data for their own purposes. More than 200 research publications have cited the eBird data. You could even use the data yourself, for a project about your favorite bird or local region.

Data classification

Another type of citizen science project asks the public to help in classifying vast amounts of collected data, like photos and sounds. Many of those projects are hosted on Zooniverse, a platform with dozens of citizen science projects and more than a million participants.
For the Wild Gabon project, volunteers identify animals in the Lopé National Park based on photos taken by motion-triggered cameras.
Here's one example where I managed to spot a gorilla:
Screenshot from animal identification task in Wild Gabon project. The left side shows a photo of a gorilla walking through a forest. The right side shows a list of animal names with photos, and "Gorilla" is selected.
Not all photos have animals that are clearly identifiable as that gorilla, however, so volunteers might mis-classify the animals in a photo. To compensate for that, the platform gives the same photo to multiple volunteers and comes up with a final classification based on the consensus.
Citizen science projects are successful because they harness the effort of huge numbers of volunteers. The average person may not have the training and expertise of a scientist, but if enough people have the time and energy, they can make large contributions to scientific research.

Volunteer computing

Don't have the time to contribute to a citizen science project? Well, maybe your computer does!
In volunteer computing, people donate their computer's spare resources to crunch numbers for scientific research projects. Volunteer computing applications monitor how much of the CPU is needed for the user's applications and uses the leftover CPU for its own data analysis.
SETI@Home is the most well-known volunteer computing project. It's a computer program that analyzes the signals from radio telescopes for signs of intelligent life in the universe. Anyone can download the program—and millions have!—and let it run whenever their computer has spare cycles.
Screenshot from SETI@Home application. Shows what data it's working on, how much CPU time it's using, a graph of the data analysis, and the user information.
SETI@Home shows its current data analysis and time taken.
That project inspired many more like it. Volunteers can contribute their idle CPU time to a variety of research areas, like finding better drugs to treat diseases with Folding@Home.
Screenshot from Folding@Home application. A bar shows percentage of CPU in use (1.18%), another bar shows power as "medium". There are two options labeled "When": "While I'm working" and "Only when idle", and the first option is selected. An ETA is displayed on 11 hours and 8 minutes.
Folding@Home shows its current work task and its CPU usage.
Home computers may not be very powerful on their own, but when all those home computers are combined, they become one of the largest supercomputers in the world.
Thanks to volunteer computing software (and volunteers!), scientific research projects now have a way to tap into that distributed supercomputer.

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