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Gaia: Early Views, Big Prospects

We have several months yet before the European Space Agency’s Gaia mission enters its five-year operational phase. But you can see an important milestone in the image below. Gaia’s two telescopes have to be aligned and focused as its other instruments are calibrated. Testing involves downloading data like this image of NGC1818, a young star cluster in the Large Magellanic Cloud. The image covers an area something less than one percent of the spacecraft’s full field of view. Launched on December 19, 2013, Gaia now orbits around the L2 Lagrangian point some 1.5 million kilometers from Earth.


Image: A calibration image from Gaia is part of early testing of the mission’s systems. Credit: ESA/DPAC/Airbus DS.

Gaia inevitably makes me think of Hipparcos, an earlier ESA mission launched in 1989 devoted to precision astrometry, the measurement of proper motions and parallaxes of stars to help us figure out their distance and tangential velocity. What a far cry Hipparcos was from the days when Thomas Henderson, then observing at the Cape of Good Hope, was trying to measure the parallax of Alpha Centauri, all the while dueling with the German astronomer Friedrich Wilhelm Bessel to demonstrate that the method could give us a distance measurement to a star.

Bessel’s work on 61 Cygni took precedence but both astronomers proved that the closest stars could be measured using the instruments of their day. But measuring star positions from the ground has always been tough thanks to atmospheric effects and instrument limitations. And as we looked further and further from our own stellar neighborhood, these methods grew more challenging still, which is why proposals for a space mission devoted to astrometry began as early as 1967. The Hipparcos Catalog was released in 1997, covering precise measurements of almost 120,000 stars, with less precise readings on about a million more.

Now we have Gaia, which will chart 10,000 times as many stars as Hipparcos, with measurements of their position and motion that are 100 times more accurate. If all goes well, we should wind up with the largest three-dimensional map of the Galaxy ever created, charting one billion stars in terms of their distribution, brightness, temperature, composition and motion. Gaia should firm up our understanding of galactic structure while making numerous exoplanet finds and uncovering vast numbers of brown dwarfs. We can expect measurements of 500,000 quasars in the distant universe and, much closer to home, data on new asteroids.

It’s an ambitious mission, one that contains twin optical telescopes and their imaging system, a radial velocity spectrometer and blue/red photometers. The telescopes will focus their light onto a 106 CCD focal plane array with almost one billion pixels, making Gaia’s the largest digital camera yet deployed in space. The two telescopes will monitor each target star about 70 times over the five year mission, sweeping the entire sky in the process, their repeated measurements teasing out the parallax and true motion of each object. Objects down to magnitude 20 are in range, and according to this ESA backgrounder, the accuracy will range from 20 percent for stars near galactic center to 0.001 percent for stars closest to the Solar System.

Every one of Gaia’s billion stars will have been observed in the first six months of operations once calibrations are completed, but it’s the repeated observations over five years that will allow accurate determination of stellar distances and motion, with the final catalog not scheduled to be released until three years after the end of the mission. We need to keep a close eye on Gaia. It is essentially bringing our fuzzy maps of the Milky Way into much higher resolution, with implications for existing work like Kepler’s — Gaia will be able to give us accurate information about distance and motion for the planet-bearing systems Kepler has thus far found. A million gigabytes of data are in store as Gaia’s enormous catalog deepens our view of the galaxy.


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  • Peter Chapin February 18, 2014, 14:55

    I think Gaia is the most exciting space mission launched in recent times excepting, perhaps, Kepler. Kudos to the ESA for their success with the mission so far. I am very much looking forward to the results!

  • David A. Czuba February 18, 2014, 17:00

    I was ruminating on the recent debate between Planetary Society president Bill Nye and the Creation Museum’s Ken Ham, trying to think of one simple example to show young Earth proponents that the universe is quite older than 6,000 years. Given that Dr. Ham tends to make a distinction between ‘historical science’ and ‘observational science’, the observational evidence from stellar parallax measurements fits both criteria, which the Gaia instruments will determine for stars in the tens of thousands of light year range. Any ninth grader can use trigonometry to find these stellar distances using Gaia’s orbital baseline. Even accounting for parallax error, Gaia’s optical precision should reveal that light from these objects must have been impinging on Earth for well over 6,000 years, with or without observers (whether you subscribe to John Wheeler’s participatory anthropic principle or not). The two things a creationist will find difficult to dispute are the speed of light and simple math. When Gaia goes fully operational and gives us its first coterie of data, we will have reliable parallax measurements that pin stars beyond the limitation of current data (about 1,600 light years).

    There are other simple rebuttals to a young Earth, of course. These tend to rely on geological time measurements, which become less easy for the average citizen to confirm for their own beliefs. Ice cores, tree rings, and other layered features provide great simple examples of time frozen in time. Deep ice cores like that from the European Project for Ice Coring in Antarctica go back 890,000 years, embedded with sun cycle data. Off the Pacific Northwest Coast, drilling to reveal how far back seashelf slides have occurred due to tectonic movement may pinpoint when Crater Lake exploded (approximately 7,500 years ago). Tying that event in with a human record would be a great nail in the lid, but there again the argument doesn’t require it.

    So, when you encounter someone with whom you begin to debate the age of the Earth, think of this as your 30 second argument: parallax and ice cores. Keep it simple, and don’t get bogged down in the unreliability of carbon dating or fossil layers that were upended so that primates lie below dinosaurs. Stay away from localized floods like Lake Missoula or the Bosphorus. The answer is in the stars themselves.

  • Doug M. February 18, 2014, 18:21

    Yeah, GAIA is awesome. We’re going to have to wait a while for the results, but when they come they’re going to revolutionize whole fields.

    Doug M.

  • Enzo February 18, 2014, 22:17


    Creationists are people who set whatever the bible has to say to TRUE and then proceed to derive their own reality from that. Discussing with them is futile.
    For example, what is the logical conclusion if both the world is 6,000 years old and the stars appear to be thousand of light years away ? That the speed of light must have slowed down a lot in the last 6,000 years. And I think that this is indeed what they preach.
    Another example : the ark dimensions are given in the bible and, by their own teachings, all animals were created in a few days. Unfortunately all the animal pairs do not fit at all (not to mention the logistic of feeding them). Keep in mind that, with that much fresh water raining down, all marine and freshwater animals (for different reasons) would have had to be on the ark too.
    When I pointed this out to three different creationists, I got the following answers :
    “They fitted for sure!!!!”
    “They did fit and that’s all we need to know”
    “Couldn’t have god made all animals small, just like Japanese make smaller things ?”

    Such are creationists.
    “How could a god create a beast so low ? I would I know” – Lloyd Cole – Standards :-) (Apologies to Lloyd that refers to humanity in general, not just the creationists)

  • Enzo February 18, 2014, 22:20

    Sotry the correct quote is :
    “How could a god create a beast so low ? How would I know”

  • Ronald February 19, 2014, 6:59

    Gaia is indisputable an awesome instrument.

    However, with regard to David A. Czuba’s nice argumentation (with which I fully agree, btw): no scientific discovery will convince the fundamentalist believer, because fundamentalist believers (of any creed) believe what they wish (or feel obliged) to believe, and will always ‘explain’ (or rather: try to bend) reality according to those beliefs.

    Example: I have heard fundamentalist believers with a basic knowledge of the vastness of the universe claim that this meant nothing with regard to the age of the universe, because all that was indeed created some 6000 years ago, *with the light also created already on its way to earth* (!).

  • kzb February 19, 2014, 8:45

    David: I doubt very much that Gaia will be the final nail in the coffin of creationism ! That lid was nailed shut to any reasonable person many decades ago. (If all argument fails, Gaia will simply be another plot by the satanist EU to undermine the word of God.)

    Unfortunately I might be giving them some ammunition here. Micro-arcsecond parallax measurements to very distant objects have been available for some time time, via the VLA (very large array). However some VLA distances are discrepant with Hipparcos. The distance to the Pleides is a different number to the VLA and Hipparcos.

    The VLA people seem to be saying there is some unknown systematic with Hipparcos data, and since Gaia is from the same organisation, that systematic problem with Hipparcos might carry on into Gaia. (Notice they don’t mention a possible systematic with VLA though !)

  • Ronald February 19, 2014, 9:34

    Further to GAIA: although this instrument will be great for astrometry and a very worthy successor of Hipparcos, when it comes to (earthlike) planet detection around nearby stars, I am more looking forward to near future RV instruments, successors to HARPS, in particular:
    ESPRESSO, to be installed on the VLT in 2016: http://en.wikipedia.org/wiki/ESPRESSO
    CODEX, to be installed on the E-ELT around 2022: http://en.wikipedia.org/wiki/E-ELT#Instrumentation

    With these we will for the first time be able to detect truly earthlike planets in earthlike orbits around sunlike stars.

  • Ronald February 19, 2014, 11:04

    Enzo: “Creationists are people who set whatever the bible has to say to TRUE and then proceed to derive their own reality from that.”

    One of the best statements ever, but I would generalize this a bit further to ‘fundamentalists’ and ‘whatever their believe system has to say’.
    And add: “, and choose to deny or ignore whatever conflicts with their views”.

    I found this generally to be true among all fundamentalist believers (fundamentalist defined as something like ‘having one’s worldview be determined by one’s religious or spiritual convictions’), also so-called modern varieties, such as anthroposophy, new-age, scientology, etc. etc., even some formally non-religious radical therapies, such as ‘The Secret’.

    I have come to the conclusion that it is a way of thinking and viewing the world around us, which is in turn, besides being determined by culture and upbringing, probably structured somewhere in the brain. So, indeed very fundamental in more than one way.

    My impression is that this way of thinking is found more among low-educated than high-educated, but also more among ‘alpha/gamma’ thinkers (languages/social sciences) than ‘beta'(natural sciences, technology).

  • ljk February 19, 2014, 11:48

    A very recent survey says that 1 in 4 Americans still think the Sun goes ’round the Earth, so do you honestly think they are going to have a grasp or care about what the data from Gaia has to say?


    It’s only been, what, about 2,200 years since Aristarchus of Samos came up with the heliocentric theory – and was apparently punished for religious impiety for the concept.

    Giordano Bruno was burned at the stake in 1600 not directly for saying that every star is a heliocentric system with planets that have life on them, but it did not help his case, to be sure.

    Now I understand even better what the fictional ETI in the film version of Contact meant when he said “Small moves” to Ellie Arroway.

  • Ashley Baldwin February 19, 2014, 14:32

    I’m not entirely clear on what the Gaia astrometry will bring in terms of exoplanets. The ESA mentions around a thousand exoplanets on its webpage but isn’t clear as whether these will be new , previously unknown planets or provision of more precise data ( position, mass) on previously known planets . My guess is both but I’m interested in how many new planets will be discovered . Do the ESA mean up to a thousand?

  • andy February 19, 2014, 14:48

    Talking of HARPS and ESPRESSO, these have significant involvement from Switzerland. So far the first consequence of the recent Swiss referendum to impose quotas on EU migrants (which will have knock-on effects on various agreements between Switzerland and the EU) has been the suspension of talks on research funding between the EU and Switzerland – anyone heard anything about what will happen to the HARPS and ESPRESSO projects?

  • Ashley Baldwin February 19, 2014, 18:38

    CHEOPS too.

  • NS February 20, 2014, 2:46

    Although Noam Chomsky is a scientist and a humanist, he has a more nuanced view of religion than many with basically similar views express [audio file]:


  • kzb February 21, 2014, 8:33

    On Andy’s point -what about CERN ?

    Correction to my previous post here: I meant VLBA (very large baseline array ?) not VLA of course.

  • ljk February 21, 2014, 10:35

    ESO VST images Gaia 1.5 billion kilometers past Earth’s orbit, one million times fainter than what the unaided human eye can see:


    Bonus – Poster on open star cluster to be surveyed by Gaia-ESO:


  • stephen February 21, 2014, 11:27

    I hope you know not all religions=Fundamentalist ignoramuses.

    Hildegard of Bingen, Pope Sylvester, Roger Bacon….

    If fundamentalists took over the government completely, instead of a deadlock between Republicans and Democrats, there would be a deadlock between young-earth creationists and old-earth creationists, and between…God made fossils to test our faith and Satan made fossils to deceive us.

  • josh March 4, 2014, 4:46

    I used to be Baptist. I was raised in a conservative religious environment and have many “fundamentalist” acquaintances but just as many that have drifted away from religion over time like myself. Therefore, I take exception to the claims that religious people cannot be reasoned with and cannot change their minds in light of scientific evidence and convincing arguments. I find it worrisome that these claims are often taken almost to the extent of dehumanizing religious people, treating them as animals that don’t have use of universal human faculties of reason.

    Even many regular church-goers that I know harbour private doubts that they confide to their friends but don’t air publicly because they don’t want to grieve their families. Nominal religious adherence without deep-seated conviction is widespread, and yes, even among “fundamentalists.”

  • ljk June 17, 2014, 8:59

    Gaia Space Telescope Team Battles ‘Stray Light’ Problems At Start Of Mission

    by ELIZABETH HOWELL on JUNE 16, 2014

    Europe’s powerful Milky Way mapper is facing some problems as controllers ready the Gaia telescope for operations. It turns out that there is “stray light” bleeding into the telescope, which will affect how well it can see the stars around it. Also, the telescope optics are also not transmitting as efficiently as the design predicted.

    Controllers emphasize the light problem would only affect the faintest visible stars, and that tests are ongoing to minimize the impact on the mission. Still, there will be some effect on how well Gaia can map the stars around it due to this issue.

    Full article here: