The Gaia Mission¶
Display data from Gaia
All thanks to the European Space Agency for data and images such as this.
This module uses the astroquery.gaia submodule to query the Gaia database.
I am still finding my way around the data (almost June 2020).
It is a record of over a billion observations.
Many variables, along with error estimates too.
The plan for now is to download a bunch of random samples, asynchronously.
Save each sample in fits format.
And then explore the data.
Data downloaded is cached in the current directory.
The same is checked for data from a previous run and that will be read in before loading any further data.
Would be good to be able to be able to share bunches of data, that is part of the more general problem of distributed data.
See -bunch and -topn command line options for how to control how many bunches are downloaded and how big each bunch is.
The idea here is to look into the question, of just where is the sun?
Specifically, where is it relative to the galactic centre?
Recognising that the galactic centre is a bit of a puzzle itself.
2024/4/29¶
In a recent paper X. Ou et al. https://doi.org/10.1093/mnras/stae034 used Gaia and other data sources to calculate a galactic rotation curve for the Milk Way.
The finding was that the galaxy had a typical rotation curve, rising linearly to 200km/s, remaining at that velocity out to 25kpc. After that point the found a steady drop in tangential velocity.
Xiaowei was kind enough to provide code (https://github.com/aceilers/spectroscopic_parallax) which shows how to set up astropy coordinates for each Gaia observation based on a given location of the galactic centre.
The code now has a –download option, that will download the Gaia observations for all stars for which there is a non-null radial velocity into a number (default=1000) of bunches.
This splits the ~34 million observations into separate files that are downloaded using separate queries. It is likely there will be timeouts and failures, but you can start looking at the data as soon as a few bunches have been downloaded.
It is recomended to create a fresh folder, cd to that folder and then run:
python3 -m gotu.gaia –download
You can then run:
python3 -m gotu.gaia
To view the bunches that have been downloaded, the full dataset is not needed to get a good qualitative feel for what is going on.
Please be nice to the Gaia servers. TODO: look into options for sharing tables on Gaia servers. Also, how to summarise the data? Bin counts?
At the console prmompt enter:
magic.show()
Milky Way Rotation Curve¶
The bottom 35 bits of the Gaia source_id encodes the Healpix pixel number that the source lies in.
Currently going through gymnastics to get all this working nicely, it opens up lots of interresting ideas for simulation.