A new video from the European Southern Observatory’s video podcast, ESOcast, takes viewers through the history of the various types of sensors that humans have used to record starlight. The video is hosted by ESO astronomer and ESOcast host Joe Liske (aka Dr. J).
The earliest of these sensors shouldn’t be that hard to guess, according to Liske: It was the human eye.
“It wasn’t until the early 17th century that we started to use a tool to help us see fainter and more distant stars,” Liske said in the video. That first tool was, of course, the telescope. Galileo Galilei was one of the first scientists ever known to have used a telescope, which he used back in 1609 to peer into the cosmos.
A telescope helped Galileo identify Jupiter’s four largest moons, revealing that Earth was not the only planet with a lunar companion. According to Liske, this discovery “forever changed our view of our place in the universe.”
Unfortunately for Galileo and his contemporaries, it wasn’t yet possible to use a machine to capture what they saw through the telescope, and scientists of the day had to draw what they saw.
It wasn’t until about 230 years later that astronomers could use photographic plates to detect and record light from space.
“Photographic plates can be exposed for hours on end, allowing astronomers to detect much fainter objects than was possible by eye,” Liske said. The plates also gave astronomers the first “faithful” image of the stars, which eliminated the human error involved in a sketch.
Still, scientists pushed for more sensitive recording devices as technology got better. When electronics “entered the picture,” according to Liske, photomultiplier vacuum tubes again changed the way scientists looked at the night sky.
The tubes, which were available in the 1930s, convert a photon into an electron, which is multiplied to generate an electrical current and amplify the photon’s signal. The photomultipliers were about 10 times more sensitive to light than photographic plates, according to Liske. But they were difficult to use for imaging purposes.
When digital imaging became possible in the 1970s, that was no longer a problem. Digital imaging uses light-sensitive semiconductors called charged coupled devices (CCDs). They’re made up of a “thin layer of silicon that is divided into millions of tiny squares, each representing a pixel.”
We still use CCDs today, though they have gotten much more sensitive than they were in the 1970s — the ones used for astronomy have also become much larger , according to Liske. Today, they can be as large as 9,000 by 9,000 pixels (or 81 megapixels) and can be put together to create a camera able to capture more than a billion pixels.
“As the technology continues to develop, we can look forward to future detectors that will be even better at capturing the faint drizzle of light from the cosmos,” Liske said.
Space.com senior producer Steve Spaleta contributed to this report.