I How Does the GAIA Program Count 1.7 Billion Stars in Its Image?

[nmsurobert]

I just an read article on the ESAs Gaia program. I was wondering how they count the 1.7 billion stars in the image? Are the stars cataloged as the images are taken? Or is there a method that is used after the images have been collected?

http://sci.esa.int/gaia/60169-gaia-s-sky-in-colour/

 

[glappkaeft]

Other way around, GAIA don't really capture images in the traditional sense. The image is a visualization of the data captured by GAIA (position, radial velocity, proper motion, color etc.).

 

[nmsurobert]

Other way around, GAIA don't really capture images in the traditional sense. The image is a visualization of the data captured by GAIA (position, radial velocity, proper motion, color etc.).

So when data is collected through the CCD camera, the data be turned into a graph... or something? ccds create images from potential differences, right? I am guessing the stars create potential differences and those can be counted?

 

[glappkaeft]

So when data is collected through the CCD camera, the data be turned into a graph... or something?

GAIA's optical system, camera and data reduction is rather unusual and very specialized. It throws away most of the image data and only sends the interesting bits to Earth where it is processed by super computers that takes many measurements (on the top of my head around 80 or more) over several years of each star to build a database of stars (and some other objects) and their properties. There is a good primer article and video at:
http://sci.esa.int/gaia/53281-inside-gaia-s-billion-pixel-camera/

ccds create images from potential differences, right? I am guessing the stars create potential differences and those can be counted?

You are in the right neighborhood at least. Very loosely a pixel in a digital sensor (CMOS or CCD) is a tiny solar panel that turn every detected photon into one electron which it stores until it is ready to count them. Exactly how this is done depends on the technology used and especially the way the electrons are moved and read out of a CCDs pixels (the so called Bucket Brigade) give you several tricks to use. GAIA uses one of these tricks to do Time Delay Integration which gives it very good sensitivity even though the image of the stars trail across the senor as GAIA rotates:
https://en.wikipedia.org/wiki/Time_delay_and_integration

 

[nmsurobert]

GAIA's optical system, camera and data reduction is rather unusual and very specialized. It throws away most of the image data and only sends the interesting bits to Earth where it is processed by super computers that takes many measurements (on the top of my head around 80 or more) over several years of each star to build a database of stars (and some other objects) and their properties. There is a good primer article and video at:
http://sci.esa.int/gaia/53281-inside-gaia-s-billion-pixel-camera/
You are in the right neighborhood at least. Very loosely a pixel in a digital sensor (CMOS or CCD) is a tiny solar panel that turn every detected photon into one electron which it stores until it is ready to count them. Exactly how this is done depends on the technology used and especially the way the electrons are moved and read out of a CCDs pixels (the so called Bucket Brigade) give you several tricks to use. GAIA uses one of these tricks to do Time Delay Integration which gives it very good sensitivity even though the image of the stars trail across the senor as GAIA rotates:
https://en.wikipedia.org/wiki/Time_delay_and_integration

ah ok. Thank you! This helps a lot.