According to a press release from Yale, the galaxies are 10 times smaller than the Milky Way galaxy and 100 times less massive. But despite their small size, they are forming stars 10 times faster than our galaxy.
There are about 1 million galaxies in the project's image bank, but only 250 "Green Peas" have been found. (The volunteers who found them started to call themselves the "Peas Corps" and the "Peas Brigade.")
"No one person could have done this on their own," Cardamone said. "Even if we had managed to look through 10,000 of these images, we would have only come across a few Green Peas and wouldn't have recognized them as a unique class of galaxies."
It's not just modern-day amateurs who have made significant contributions to astronomy.
When William Herschel discovered the planet Uranus in 1781, he was a middle-class musician who pursued astronomy as a hobby.
"As a result of discovering Uranus he came to the attention of the scientific community," said AAS' Maran. At that point, he was introduced to King George III who put him on salary.
Other astronomers had observed Uranus before but thought it was a star. When Herschel observed it with a telescope he designed and built himself, he realized that in fact is was the seventh planet from the sun.
In 1993, Carolyn and Gene Shoemaker and David Levy discovered a comet orbiting Jupiter. About a year later, the Shoemaker-Levy 9 struck Jupiter, generating awareness about the possibility of cosmic objects colliding with Earth.
Although he is now a decorated astronomer, at the time, Levy was an amateur astronomer and science writer.
"He's probably best known as a writer of astronomical science books. He's very well trained, he just makes his living in a different way," said Roger Launius, a NASA space historian. "That's an example of an amateur who has had an enormous impact."
The Canadian-born skywatcher has discovered 22 comets, which puts him in a tie for third place in history for the largest number of comets found by an individual.
He now works with the Jarnac Comet Survey, based at the Jarnac Observatory in Vail, Ariz.
John Dobson is considered one of the most influential amateur astronomers, but not because of something he spotted in the sky. The astronomy enthusiast is credited with designing a telescope that made skywatching more affordable and accessible.
"The Dobsonian telescope -- what an amazing contribution that is," said ASP's Gurton. "Amateur astronomy can be an expensive hobby. That design just shattered the price. It's so simple, you can make your own for a fraction of the price."
Dobson, who was born in China in 1915, earned a degree in chemistry and worked in defense-related industries. But because of an abiding interest in astronomy, he tinkered with telescope design, building his first one in 1956.
His design favored low-cost, easily-accessible materials over traditional components. For example, instead of aluminum or fiberglass telescope tubes, Dobson chose thick paper tubes used in construction to pour concrete columns.
Gurton said he also popularized "sidewalk" or "commando" astronomy, which involved setting up portable telescopes in urban areas to give others the opportunity to view the night sky.