Comment by lysace
3 days ago
Gaia has a 1.0 × 0.5 m focal plane array on which light from both telescopes is projected. This in turn consists of 106 CCDs of 4500 × 1966 pixels each, for a total of 937.8 megapixels.
Neat.
3 days ago
Gaia has a 1.0 × 0.5 m focal plane array on which light from both telescopes is projected. This in turn consists of 106 CCDs of 4500 × 1966 pixels each, for a total of 937.8 megapixels.
Neat.
The really neat part is the instrument precision. It's terrifyingly good and I have no idea how it (really) works.
- "Gaia measures their positions to an accuracy of 24 microarcseconds, comparable to measuring the diameter of a human hair at a distance of 1000 km"
https://www.esa.int/Science_Exploration/Space_Science/Gaia/C...
To nitpick with the grammar in the quote: It's capable of measuring to the accuracy of 120 μm at 1000 km. So it cannot accurately measure the diameter of a human hair (which ranges from around 20 to 200 μm) at that distance, but only to the accuracy of a human hair.
You're right: this precision is hundreds of times below the diffraction limit of even the James Webb telescope. It can't possibly measure the width of an object that finely; rather, only the relative displacement of its centroid position between two points in time. (And it's a seriously confusing physics miracle that that much is possible).
2 replies →
It takes about 14 pictures of each star during orbit (which is quite close to Earth’s orbit around the Sun), so approximately once per month, and then compares those to calculate the star’s distance from the parallax.
Isn't that just the distance between pixels and the image projected onto them?
Probably not. The accuracy with which you know the pointing of the telescope probably also plays into it (unless the FOV is large enough to have other stars as a reference?), and you can do subpixel positioning of objects to get more accuracy than full pixel steps.
No: it's far weirder and I'm not knowledgeable enough to explain it.
And Gaia also has a downlink speed of approx 3Mbps. So it will process as much as possible on board and just send down less than 20 pixels per each star imaged. That is why you can not get a direct image out of it.