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71 votes
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Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?

Well, you thought about the spatial aspect of a parallax measurement, but not about the temporal one. Gaia's intention is to measure 3D positions as well as 3D velocities. For the distance, you need ...
AtmosphericPrisonEscape's user avatar
54 votes

Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?

I think it is to do with (a) orbital speed and (b) telemetry and (c) power. In order to measure Parallax you need to measure the position of the star from different locations in the solar system. The ...
ProfRob's user avatar
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21 votes
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Why not send a Gaia-like mission to Mars?

The panels need to be about 2.3 times bigger to generate the same power. The telemetry requirements are limited by distance to some power, assuming that the communications beam cannot be infinitely ...
ProfRob's user avatar
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11 votes
Accepted

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

The Ca triplet in the near infrared are extremely strong resonance absorption lines. They are by far the strongest features in the near infrared spectra of cool G,K,M type dwarfs and giants, which ...
ProfRob's user avatar
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9 votes

What is the proper interpretation of a negative parallax?

Did you read this section of the documentation? It suggests there are ways to deal with it, but I have not examined the paper it refers to. • For closely aligned sources (separated by 0.2–0.3 ...
BowlOfRed's user avatar
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9 votes
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Has GAIA learned anything about General Relativity looking near Jupiter? (Gerry Gilmore: "oblate rotating mass moving in a deeper (Solar) potential")

Gaia is the follow-up to the Hipparcos mission, which was deactivated in 1993. So Gaia's results are decades in the making. The word "Gaia" was originally an acronym for "Global ...
Daddy Kropotkin's user avatar
8 votes
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How can I calculate the uncertainties in magnitude like the CDS does?

That is because what is measured is a flux and the flux errors are in the DR2 catalogue. Since magnitudes are based on the logarithm of the flux, then there is no straightforward correspondence (...
ProfRob's user avatar
  • 152k
7 votes

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

The ESA states it pretty clearly (although their figure of 855.2 nm is incorrect; it should be 866.2 nm): The RVS wavelength range, 847-874 nm, has been selected to coincide with the energy-...
HDE 226868's user avatar
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7 votes
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Why (the heck) is the basic angle of GAIA 106.5°?

The choice of basic angle in Hipparcos and Gaia is related to the "rigidity" of the stellar reference system that can be constructed when connecting accurate positional measurements across ...
MichaelP's user avatar
  • 386
6 votes

Gaia Parallax data

Gaia data release 1 was announced in September 2016. It has parallaxes for 2 million stars previously observed by the Hipparcos mission, a small fraction of the 1.1 billion positions recorded so far. ...
Mike G's user avatar
  • 18.7k
6 votes

Why does Gaia use only calcium NIR lines for stellar radial velocity measurements?

According to Cropper and Katz 2011 part 2.2, the RVS working group considered other bands, but the ~850 nm band is relatively unaffected by absorption in the Earth's atmosphere, facilitating ground-...
Mike G's user avatar
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5 votes
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Why no Polaris distance in GAIA DR2?

My query for stars north of +75° and brighter than magnitude 4 returns only 6 stars, brightest of which is γ Cephei. Polaris may be too bright for Gaia. Even if it doesn't saturate the detector, a ...
Mike G's user avatar
  • 18.7k
5 votes

What is the proper interpretation of a negative parallax?

It depends how negative the parallax is and what your "prior" knowledge is of the distance to the star. As another answer suggests, there are some spurious large negative (and positive) ...
ProfRob's user avatar
  • 152k
5 votes

Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?

3 problems. 1) Time. As previous answers say, to make use of the larger diameter around the sun at Neptune's L2 point, you need to wait for a full rotation which takes 168+ years. 2) Energy. Solar ...
eagle275's user avatar
  • 311
5 votes

Did Gaia actually generate complete light curves for 212 Cepheids in other galaxies?

Am I naive to think that it is necessary to build up a nice, complete light curve with dense points in time in order to use the photometry for precision distance calculations? No, the more I read ...
Alex's user avatar
  • 2,265
5 votes
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How many stars can we resolve?

I tried to get a estimate for an upper-bound with currently deployed instruments. Assuming that, resolution-wise, the James Webb Space Telescope is the best telescope we have today, I looked into its ...
ksousa's user avatar
  • 1,201
5 votes
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How to get star position from the Gaia data set?

Astronomy uses typically an Earth-centered (or solar system barycentric) spherical coordinate system with right ascension (RA, $\alpha$) ranging from 0 to 360° and declination (DEC, $\delta$) from -90°...
planetmaker's user avatar
  • 19.4k
4 votes

Calculating the distance of objects using the Gaia DR1

The early 1990s Hipparcos mission yielded parallaxes for 118000 stars (Hipparcos catalog) and positions without parallax for another 2.4 million (Tycho-2 catalog). The Tycho-Gaia astrometric solution (...
Mike G's user avatar
  • 18.7k
4 votes

Will Gaia detect inactive neutron stars?

I will throw out a suggestion that could hardly be considered an "answer", but it would be interesting if someone could put flesh on the bones of it. When I first read your question I thought you ...
ProfRob's user avatar
  • 152k
4 votes
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Very near GAIA DR2 sources - has Proxima Centauri been dethroned?

These are spurious data points. They are likely genuine objects, but the parallax value is incorrect. There are a small number of these in the Gaia data set. There are 59 object with a parallax ...
agabrown's user avatar
4 votes

How many GAIA Data Release 2 files are there?

There are 61,234 data files in the directory. There are three additional (non-data) files: MD5SUM.txt _citation.txt _disclaimer.txt If you include those, ...
Demitri's user avatar
  • 236
4 votes

What is the proper interpretation of a negative parallax?

Negative parallaxes can be interpreted as the observer (in this case Gaia satellite) going the "wrong way around the sun" as mentioned in this Jupyter Notebook by Anthony Brown. This notebook is meant ...
nmg's user avatar
  • 41
4 votes

What is the proper interpretation of a negative parallax?

Although should not use the negative parallaxes, you should not ignore them either. If you are looking at populations of objects, removing those with negative parallaxes will lead to significant bias ...
Andrew's user avatar
  • 41
4 votes

Why is Gaia operating around Earth orbit? Why not send it to Neptune's orbit?

One could certainly send a Gaia-like spacecraft into deep space, and take parallax measures at all times along its orbit. This is unattractive for several reasons, however. In short the large ...
Tod R. Lauer's user avatar
4 votes
Accepted

How can GAIA's accuracy for position, parallax, and annual proper motion for a given star be the same number?

Parallax and proper motion are determined from a series of position measurements taken over the course of (for Gaia DR2) 22 months. A "5-parameter" astrometric model is fitted to these position ...
ProfRob's user avatar
  • 152k
4 votes

Fits file re-alignment

I ended up making my own small code that you can find here: https://github.com/crhea93/AstronomyTools/blob/master/Astrometry/Correction.py Essentially, after inputting at least 3 matching ...
Carter Rhea's user avatar
4 votes

Approximate spectral type and luminosity given apparent magnitude and distance

You can calculate the absolute magnitude of a star: $$M=m-5\log_{10}(\frac{d}{10\,\text{pc}})$$ where $M$ is absolute magnitude, $m$ is apparent magnitude and $d$ is the distance. Then you take a look ...
User123's user avatar
  • 2,879
4 votes

Why (the heck) is the basic angle of GAIA 106.5°?

I did not find anything conclusive on the web, and I am yet waiting to receive feedback from ESA's contact page. In a German speaking IT forum there is something a bit less vague than the FAQ cited in ...
B--rian's user avatar
  • 5,616
4 votes
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Extracting specific star data from Gaia DR2?

You can do this via VizieR (main site at CDS, Strasbourg, France linked; worldwide mirrors are available). You can search by catalog name from that form or enter ...
astrosnapper's user avatar
  • 8,357

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