The switch has been thrown on a telescope specifically designed to seek out alien life.
The array will be able to image large sections of the sky at once
Funded by Microsoft co-founder Paul Allen, the finished array will have 350 six-metre antennas and will be one of the world's largest.
The Allen Telescope Array (ATA) will be able to sweep more than one million star systems for radio signals generated by intelligent beings.
Its creators hope it will help spot definite signs of alien life by 2025.
The ATA is being run by the Seti Institute and the Radio Astronomy Laboratory from the University of California, Berkeley, US
"For Seti, the ATA's technical capabilities exponentially increase our ability to search for intelligent signals, and may lead to the discovery of thinking beings elsewhere in the Universe," said Seth Shostak, senior astronomer at the Seti Institute in a statement.
On 11 October, the first 42 dishes of the array started gathering data that will be analysed for signs of alien life and help with conventional radio astronomy.
The first test images produced by the array are radio maps of the Andromeda Galaxy and the Triangulum Galaxy.
The ATA is pioneering a novel design.
Mr Allen provided the funding for the first stages of the array
Rather than being hand built, each six-metre antenna is made of a mass-produced dish and off-the-shelf components. Behind the scenes, digital signal processing software is used to analyse data and clean out man-made interference that would otherwise make the captured information useless.
The layout of the array has also been carefully plotted so the instruments work in unison to take a single snapshot of huge swathes of the sky.
The ATA's creators claim that even with only 42 antennas on-stream, the instrument already rivals larger instruments in its ability to carry out brightness, temperature and point source surveys.
When all 350 dishes are gathering data, the ATA's creators say it will allow the gathering of data on an "unprecedented" scale.
The finished instrument will be able to study an area of the sky 17 times larger than that possible with the Very Large Array in New Mexico.
Mr Allen has provided Seti and Berkeley with a $25m grant to fund the initial construction work on the instrument. Other sponsors are being sought for the other $25m needed to complete the project.
It is expected to help improve understanding of such phenomena as supernovas, black holes, and exotic astronomical objects that have been predicted but never observed.
The array is situated in Hat Creek, California, and lies about 290 miles (470 km) north of San Francisco.