back to article Got a telescope? Bid farewell to ESA's retiring Milky Way mapper

The European Space Agency's (ESA) Milky Way mapper Gaia has completed the sky-scanning phase of its mission, racking up more than three trillion observations over the past decade. Gaia was launched on December 19, 2013, with the aim to create a three-dimensional map of the Milky Way galaxy and beyond by surveying nearly two …

  1. Eclectic Man Silver badge
    Pint

    Well done!

    A superb mission, congratulations to all concerned. The data will continue to provide surprises for a long time, I hope.

    1. harmjschoonhoven

      Re: Well done!

      All Gaia data releases are in the public domain. Download a few GByte, unzip the data and see what you 've got. It is fun without need for a telescope and clear skies :-).

      See https://www.esa.int/esearch?q=data+release+3 for animations and other predigested information.

  2. Bill Gray

    Re : amateur observations

    The original plan was that Gaia would be tracked optically by small telescopes. (Its exact position doesn't matter much for observing stars. But for analysis of the asteroid observations, you really want to know where Gaia is to within better than a kilometer or so.)

    Problem was, it turned out to be about three magnitudes fainter than expected. ESA compensated by switching to larger telescopes, which was annoying but doable, plus a bit of trickery involving the difference in reception times at two different radio telescopes.)

    ESA has posted information about observing Gaia over the next few months. (Scroll down to "perform Gaia observations yourself".) Among other things, they hope to find out why it was so $%&! faint over the last ten years. (I'm hoping it turns out to be something that can be used intentionally to keep Starlinks and similar megaconstellations dark, but that's probably a bit much for which to hope.)

    For us asteroid observing guys, Gaia has really transformed the field in two ways. The star catalog removes a lot of systematic biases that occurred in older catalogs. So when you've observed an asteroid and are measuring its position relative to other stars, a big source of error goes away. We can (for example) tell you if a near-earth asteroid is really dangerous with much greater accuracy.

    The other big advantage is that Gaia's observations of the asteroids themselves have helped a lot in predicting occultations of stars by asteroids. It used to be that we'd have a rough idea of the path of the occultation, would set up telescopes, and if we were really lucky, we'd actually be in the path. You often had to enlist observers over a big area and hope somebody got lucky.

    Nowadays, we're observing occultations almost routinely. With each one, we get a good idea of the diameter and shape of the asteroid, and sometimes even see the star blink out twice, indicating that the asteroid has a satellite. (Or, in some cases, is irregularly shaped.)

    The solar system crowd was a mere afterthought for this mission, and we still got a lot out of it. The impact on stellar astronomy has been mind-bogglingly transformative.

  3. Michael Hoffmann Silver badge
    Thumb Up

    Will the map meet regulatory requirements?

    "This map is to scale and can be used for navigation" as (for example) FAA jargon goes?

  4. Pascal Monett Silver badge

    "three trillion observations"

    Once again, stellar engineering and steadfast maintenance has brought back a wealth of information beyond all expectations.

    Why can't Redmond have that level of excellence ?

  5. Michael H.F. Wilkinson Silver badge
    Thumb Up

    Great work!

    Great mission which will keep some colleagues of mine busy for quite a while, as the next data releases appear. They are studying all sorts of streams of stars that are remnants of earlier mergers of smaller galaxies with our own.

    I might well drag out the telescope (trusty old Celestron C8) to bid GAIA farewell.

    1. Bill Gray

      Re: Great work!

      Are you observing visually? ESA seems to expect ~mag 15 at brightest. That's at the faint end of what you might get with an 8-inch = 20cm telescope. Worth a try, since the magnitude appears to be a rough prediction and actual visual limiting magnitude depends on a lot of variables.

      Observe with a CCD, and you should have absolutely no trouble at all.

  6. stiine Silver badge

    So, they've passivated the satellite. How did they actually do this?

    1. Alan Mackenzie

      Surely they could have said "deactivated"? Or maybe they meant "pacified". Satellites can get violent. Who knows?

      1. Bill Gray

        'Passivated' has a very specific meaning in this situation of "got rid of all the fuel". I don't know if it involves opening a valve or just running the thrusters/engines until they stop doing anything.

        It started as a common thing for earth-orbiting spacecraft, when it was found that leftover upper stages would sometimes sit around for years before going boom. You then had a lot of small bits to track/evade.

        Gaia (like JWST) is in a halo orbit around the earth-sun L2 point. It requires periodic adjustments to keep it in that orbit, sort of like keeping a yardstick balanced on your palm. If they just abandoned it, it would eventually slide off that orbit, probably into one that would drop toward the earth. Herschel, Planck, and WMAP were in similar orbits; each was given a bit of thrust to put it into a "graveyard orbit" around the sun, one that would be reasonably unlikely to hit the earth.

        You could point out that these objects are all small; if they _did_ hit the earth, I can't say it'd matter much. But it wouldn't be a good look.

        1. Eclectic Man Silver badge

          Bill Gray > "if they _did_ hit the earth, I can't say it'd matter much. But it wouldn't be a good look."

          Yeah, but you probably wouldn't want a big chunk of it to land on your driveway:

          https://www.youtube.com/watch?v=kKFc3Np2VUw

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