Milky Way Sparkles In The Eyes Of Gaia


Here on Earth we play around with CCD cameras that boast a million pixels. But, can you imagine what a billion pixels could do? That’s the plan for ESA’s Galaxy-mapping Gaia mission. One hundred six electronic plates are being carefully integrated together to add up to the largest digital camera ever built for space… and its mission is to chart the Milky Way.

Beginning in 2013, Gaia’s five year mission will be to photograph a billion stars within our own galaxy – determining magnitude, spectral characteristics, proper motion and dimensional positioning. This information will be gathered by its charge coupled device (CCD) sensor array. Each of the 106 detectors are smaller than a normal credit card and thinner than a human hair. Put simplistically, each plate holds its own array of light-sensitive cells called photosites. Each photosite is its own pixel – just one tiny cell in the whole body of a photograph that could contain hundreds of thousands of pixels! When incoming light strikes the photosite, the photoelectric effect occurs and creates electrons for as long as exposure occurs. The electrons are then kept “stored” in their individual cells until a computer unloads the array, counts the electrons and reassembles them into the “big picture”.

And what a picture it will be…

In a period of a month, technicians managed to delicately assemble the CCD plates onto the support structure, leaving only a 1 mm gap between them. “The mounting and precise alignment of the 106 CCDs is a key step in the assembly of the flight model focal plane assembly,” said Philippe Garé, ESA’s Gaia payload manager. Upon completion, there will be seven rows of CCD composites with a main bank of 102 strictly dedicated to star detection. The remaining four will monitor image quality of each telescope and the stability of the 106.5º angle between the two telescopes that Gaia uses to obtain stereo views of stars. And, just like cooling a smaller CCD camera, the temperature needs to be maintained at -110ºC to keep up the sensitivity.

Gaia might be heavy on imaging capabilities, but she’s light on weight. The majority of the spacecraft, including the support structure is crafted from a ceramic-like material called silicon carbide. Resistant to warping in extreme temperature conditions, the whole support structure with its detectors weighs in at only 20 kg. She’ll sail out to Lagrange Point L2 – 1.5 million kilometers behind the Earth – where twin telescopes will capture perhaps 1% of our galaxy’s stellar population. While that may seem like a small amount, the information that Gaia’s three-dimensional star map will provide can reveal much more than we already know about the composition, formation and evolution of the Milky Way.

Original Story Source: ESA News.

16 Replies to “Milky Way Sparkles In The Eyes Of Gaia”

  1. At the first paragraph, there’s a missing conjunction “and” in the fourth sentence: “One hundred [and] six electronic plates…”

    1. hi, ivan! no offense, but i think it’s correct this time. try pronouncing 106. but you might be right and i’d be totally surprised if i gotcha’! 😉 english teachers? arise and tell us!

      1. I’ve done a check with Wikipedia on English numerals, and it appears that there is a style difference between American English (you) and British English (me), so either way is correct.

      2. so we are both correct… and that makes me happy! for what it’s worth, i don’t mind your corrections, because it makes me a better writer. (and how i wish you had been around to help me edit a few of my books!) i have my own personal style that doesn’t fit in with editing programs, so i don’t use them. (and a thousand people out there are thinking “it’s no wonder her writing sucks!” giggle…) having you police my mistakes makes me take a closer look and think twice about how i phrase something. needless to say it is sometimes a challenge when writing for a multi-lingual and multi-cultural audience!

        as for other’s mistakes in postings, i simply read past them because i think only i have the luxury of being able to edit once it’s submitted. how many of us have clicked the “send” button on an email only to see a really glaring error just a split-second too late?!

        oops. maybe i shouldn’t have clicked “rely all”…


      3. Thanks again, Tammy, for your appreciation; I like a woman with a good sense of humour — unlike some individuals here!

    2. Hey Ivan, nobody cares about your idiotic corrections, what is your problem? I suspect you are rather short “in a certain area”, sheesh…

      1. So, just because you cannot find any fault with my corrections, you resort to juvenile schoolyard insults. Is that all you can do?

      2. What a joke, you just dont get it. People dont care and you are making a fool of yourself EVERYTIME you attempt to correct another persons post.


        I come to this forum to expand my knowledge on all things current in the Universe, not to see Ivan3man picking on errors that dont even exist.

        Once again, take some advice and GET A LIFE.

      3. Now don’t get your knickers in a twist, dude! Also, on four occasions, you’ve neglected the abbreviation apostrophe in “dont”. Furthermore, there should be a possessive apostrophe in “persons”.

  2. Hehehe cummon Flogger lighten up… It’s just Ivan3man’s thing ok?

    Tammy nice article.

    Just a random question I am wondering about – Those technicians all mocked up in that impressive looking clean-room gear… What about those uncovered eyebrows? Wouldn’t an eyelash or an eyebrow really foul things up on the space probe’s CCD array?… I can hear the article now – Gaia probe finds new class of star with elongated light rays- ???

    Can anyone here shed [bad-pun] some light?

  3. Great article! The Gaia Mission is one of my most keenly awaited…

    Should revolutionise our understanding of the Galaxy, and help refine our distance scale significantly…

  4. The telescope has two prmary mirrors, or what looks like that, but one CCD array, which is quite extensive. The existence of two primaries I find interesting, and I was wondering what the purpose of that was.


    1. According to Wikipedia – Gaia (spacecraft):

      Similarly to its predecessor Hipparcos, Gaia consists of two telescopes providing two observing directions with a fixed, wide angle between them. The spacecraft rotates continuously around an axis perpendicular to the two telescopes’ lines of sight (LOS). The spin axis in turn has a slight precession across the sky, while maintaining the same angle to the Sun. By precisely measuring the relative positions of objects from both observing directions, a rigid system of reference is obtained.

      Each celestial object will be observed on average about 70 times during the mission, which is expected to last 5 years. These measurements will help determine the astrometric parameters of stars: 2 corresponding to the angular position of a given star on the sky, 2 for the derivatives of the star’s position over time (motion) and lastly, the stars parallax. The radial velocity of the star is measured using the Doppler Effect by a spectrometer, which is integrated into the Gaia telescope system.

      1. Thanks, I suppose I should have looked this up. I then gather that with two primary mirrors that with each rotation of the craft there is some ?? in the appearance of a star on the CCD. I presume the role of two primaries is to get a sampling rate that is at a Nyquist frequency.


      2. You’re welcome! Also, you may be interested in this PDF – “The Gaia mission: science, organization and present status” – that I’ve stumbled upon here (click on the “View PDF” button there); it goes into some detail about the “Observation principle and main technical features” at section 3 of the paper.

        Furthermore, at the ESA website, there is a high-resolution image of the GAIA focal plane here.

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