Re: [guide-user] GAIA DR1

Bill Gray Apr 15, 2017

Hi Christoph, Masaki,

Displaying Gaia-DR1 is indeed a problem. The data are
sorted in HEALPIX order. This is a rather complicated (more
complicated than it should be, in my opinion!) scheme for
organizing objects on a sphere, and it doesn't work well
with Guide (and probably not with a lot of other programs
that prefer data organized by RA/dec).

The fact that Gaia-DR1 consumes about 200 GBytes is also
a problem for many of us; it would take me weeks to download
that much. Dave Tholen has created a binary version that
brings the file size down to about 32 GBytes, and also
organizes the data in RA/dec. This isn't quite a solution
yet, but may prove to be one.

The positions for Gaia-DR1 are for epoch 2015, but this
is not really so much of a problem. It just refers to the
fact that the data come from Gaia observations made around
2015, and that there is not enough data (yet) to compute
proper motions. So Gaia-DR1 gives you a very exact idea of
where the stars in question were in early 2015, but no idea
at all about how much they may have moved since then (i.e.,
you don't have any idea what the proper motion of the star is.)

There have been a couple of efforts to fix this problem,
by matching Gaia-DR1 to older catalogs. You then have a really
exact idea of where the star was in 2015, combined with a
less exact idea of where it was a decade or two earlier.
But that combination gives you a decent value for the proper
motion. One such is the UCAC5 catalog, combining the UCAC
data (re-reduced) with Gaia-DR1 :

https://groups.yahoo.com/neo/groups/MPML/conversations/messages/32540

Another is the "Hot Stuff for One Year" (HSOY) catalog :

https://groups.yahoo.com/neo/groups/MPML/conversations/messages/32591

The name refers to the fact that in a year or so, we'll have
Gaia-DR2, which will have enough data to generate proper
motions. At that point, I think pretty much every previous
astrometric catalog will be obsolete; UCAC-5 and HSOY are
really just something to bridge that one-year gap.

-- Bill

On 2017-04-13 19:05, KODA fp6m-kud@... [guide-user] wrote:
>
>
> Hello Christoph,
>
> I downloaded GAIA DR1 to display on Guide.
> But I didn't succeeded.
>
> Problem 1
> Gaia DR1 data aren't sorted by Right Ascension.
>
> Problem2
> Epoch of Gaia DR1 data is 2015, not 2000.
>
> Does someone have good idea?
>
> Masaki Kouda, Japan
>
>
>
> On 2017/04/14 2:47, cheld93@... [guide-user] wrote:
>>
>>
>> Hello!
>>
>>
>> Since a few weeks the GAJA DR1 is available for download:
>>
>> http://1016243957.rsc.cdn77.org/Gaia/gaia_source/
>>
>> Before I downloaded ~200 GB i would ask if anybody has a TDF file for this.
>>
>> Thank you
>>
>>
>> Christoph
>
>
>