Pinpointing Gaia to enable the most accurate map ever of more than a billion stars

Pinpointing Gaia to map the Milky Way
Image, a composite of several observations captured by ESO's VLT Survey Telescope (VST), shows the space observatory Gaia as a faint trail of dots across the lower half of the star-filled field of view. These observations were taken as part of an ongoing collaborative effort to measure Gaia's orbit and improve the accuracy of its unprecedented star map. Credit: ESO

Gaia, operated by the European Space Agency (ESA, surveys the sky from orbit to create the largest, most precise, three-dimensional map of our Galaxy. One year ago, the Gaia mission produced its much-awaited second data release, which included high-precision measurements—positions, distance and proper motions—of more than one billion stars in our Milky Way galaxy. This catalogue has enabled transformational studies in many fields of astronomy, addressing the structure, origin and evolution the Milky Way and generating more than 1700 scientific publications since its launch in 2013.

In order to reach the accuracy necessary for Gaia's sky maps, it is crucial to pinpoint the position of the spacecraft from Earth. Therefore, while Gaia scans the sky, gathering data for its stellar census, astronomers regularly monitor its position using a global network of optical telescopes, including the VST at ESO's Paranal Observatory . The VST is currently the largest survey telescope observing the sky in , and records Gaia's position in the sky every second night throughout the year.

"Gaia observations require a special observing procedure," explained Monika Petr-Gotzens, who has coordinated the execution of ESO's observations of Gaia since 2013. "The spacecraft is what we call a 'moving target', as it is moving quickly relative to background stars—tracking Gaia is quite the challenge!"

"The VST is the perfect tool for picking out the motion of Gaia," elaborated Ferdinando Patat, head of the ESO's Observing Programmes Office. "Using one of ESO's first-rate ground-based facilities to bolster cutting-edge space observations is a fine example of scientific cooperation."

"This is an exciting ground-space collaboration, using one of ESO's world-class telescopes to anchor the trailblazing observations of ESA's billion star surveyor," commented Timo Prusti, Gaia project scientist at ESA.

The VST observations are used by ESA's flight dynamics experts to track Gaia and refine the knowledge of the spacecraft's orbit. Painstaking calibration is required to transform the observations, in which Gaia is just a speck of light among the , into meaningful orbital information. Data from Gaia's second release was used to identify each of the stars in the field of view, and allowed the position of the spacecraft to be calculated with astonishing precision—up to 20 milliarcseconds.

"This is a challenging process: we are using Gaia's measurements of the stars to calibrate the position of the Gaia spacecraft and ultimately improve its measurements of the ," explains Timo Prusti.

"After careful and lengthy data processing, we have now achieved the accuracy required for the ground-based observations of Gaia to be implemented as part of the orbit determination," says Martin Altmann, lead of the Ground Based Optical Tracking (GBOT) campaign at the Centre for Astronomy of Heidelberg University, Germany.

The GBOT information will be used to improve our knowledge of Gaia's orbit not only in observations to come, but also for all the data that have been gathered from Earth in the previous years, leading to improvements in the data products that will be included in future releases.

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Citation: Pinpointing Gaia to enable the most accurate map ever of more than a billion stars (2019, May 2) retrieved 14 October 2019 from
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May 02, 2019
Yeah ... it will be nice when they can wrap up the work on using pulsars for on board "space GPS".

May 02, 2019
Wouldn't this task be easier and more precise with transmitters at L4 and L5 to triangulate?

May 03, 2019
The next 'more cosmic' step of combined GPS and photogrammetric bundle adjustment should learn the challenging task of combining available range (relative and absolute time) sensing data and measured image coordinates of multiple Gaia cameras to a simultaneous adjustment of physical self-calibration parameters of 4/5-D Dynamic Universe (DU) with optical sensor parameters of all Gaia sensors and their tracking data. This requires decades or centuries old continuous mapping program using the Sun orbit around Milky Way vs Earth orbit around Sun. This way increases the multi-ray stereo bases and parallaxes to resolve the DU optical distances to objects of small values of R4,T4 and their math models as functions of C4. It is enabled by the fast solution technologies of array (unified matrix and tensor) calculus with millions or even billions adjustable parameters to fit highly overdetermined observables of Gaussian least squares.

May 03, 2019
Ummmmm, transmitters of what?

This isn't Star Trek and those aren't "sensors." Other than in the passive sense.

May 03, 2019
@Da Schneib,

Folks seem to think this is "quasar" GPS. Well, the problem is Quasars don't transmit time stamps, like our RADIO transmitters on GPS satellites. Given that they have to calibrate their measurements perfectly for this to be of any use, having an exact position derived from triangulation instead of interpolating information from telescopes with only one directional view might be helpful.

Never mind Star Trek, apparently you haven't done much land navigation in your lifetime.

May 03, 2019
@ JaxPavan 'transmitters at L4 and L5 to triangulate'

In terms of Dynamic Universe (DU) expansion of GR/QM your excellent idea addresses the 4/5-D datum transfer among nested DU energy frames. Present local GPS Earth energy frame (Earth Centered Inertial or ECI coordinates) has fooled the GR/QM community about the eternal constancy of c by the fact that the frequency of real (vs imaginary SR/GR/QM thought experimental) physical atomic clocks is reduced exactly by the same rate as the deceleration of the TRUE value of cosmic C4 expansion rate of Riemann 4-radius R4 - so the APPARENT or ECI observable local speed of light c appears constant as proven during the past decade. Having GPS radio transmitters at L4, L5 etc enables the interconnections of ECI, Sun and Milky Way centered inertial system datums in conformal photogrammetric, photometric and range sensing triangulations for 4/5-D image mapping of cosmos. It may take decades or centuries = a fraction of nano B years since T4=0.

May 04, 2019
Hey, @Jax, you're the one who said math doesn't work.

Changing your tune now? You need trig to do navigation.

May 04, 2019
@Da Schneib,

I never said math "doesn't work"? You are talking gibberish now. As far as trigonometry for land navigation, not exactly, the analogue would be taking multiple resections with a map and compass to known landmarks to determine position. Once again, you show you know nothing about navigation.

I will consider your lack of candor an acknowledgement that you now understand the added value multiple time stamped transmitters might have for determining position precisely.

Jun 20, 2019
" So NASA is trying to cut the cord to Earth with its new Deep Space Atomic Clock, which is beginning a year-long trial in space." (see eg. today's MSN web news)

Looks like NASA is waking up - hopefully finally listening to the DU related time-keeping and optical/range surveying concepts of GPS and satellite mapping pioneers.

Jun 24, 2019
In analogy to SAGA purely ECI based network adjustment, it would suffice to send some 1-4 DS atomic clocks to orbit all or most other planets to get real-time Solar range based navigation system. This fixed range based control system need be complemented with optical or photogrammetric triangulation sensors of each space vehicle. Brown reported such combined GPS/BA triangulation results of his Port Malabar test field in Florida where the photogrammetric accuracy of 7 mm exceeded the best differential GPS technology some 25 years ago to establish physical (monumented ECI land mark) control point network vs. the visual Moon network triangulation points of Apollo program. His article was published in PERS of ASPRS journal in mid 1990's.

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