Re: [guide-user] Searching URAT1 Catalogue (and Gaia-DR1)

Bill Gray Oct 11 5:58 PM

Hi Ted,

You can use Go To... Object Name (or just hit Ctrl-B) and Guide will
bring up an "Enter object name:" dialog. In this, you can enter something


For UCAC2, the "standard" prefix was 2U; for UCAC3, it was 3UC (I think
somebody was already using 3U for something else); then, with UCAC4, we
went back to 4U.

That prefix is followed by a "zone number". All UCACs were split into
zones in declination; for UCAC2 and UCAC3, the zones were 0.5 degrees high.
That made for zone numbers from 1 to 360 for UCAC3. UCAC2 only got up to
about declination +46 or something like that, so the zone numbers stopped
somewhere around 288.

UCAC4 was split into 0.2 degree strips in declination, so the zone
numbers run from 1 to 900.

After the zone number, there's a '-', then the number within that zone.

Just a heads up : as many of you doubtless know, the first data release
for Gaia (Gaia-DR1) has recently been posted. This provides very precise
astrometry and photometry for about a billion stars.

This will eventually make all other star catalogs obsolete (well, except
for some very bright stars that were saturated in Gaia). There are some
limits at present : Gaia hasn't been observing for very long, so it essentially
has only measured "where the stars are now". Parallaxes and proper motions
will come in a subsequent release. Gaia-DR1 only gives data for the cleaner
cases; they haven't tried to sort out the tangled situations with double
and multiple stars. Still, it's what we all should be using for (for
example) astrometric reductions, where the fact that only the "best"
positions are given is a benefit, not a drawback.

There are two other small hitches to Gaia. First, the raw data files,
provided here :

tip the scales at over 200 GBytes, in compressed form (still larger
once decompressed, about 500 GBytes). The data are split into 5231 files,
each containing 170579 stars (except for the last one, which just contains
the last few leftover stars).

The second hitch is that the order of the stars looks to be almost
completely random. It isn't; the stars are ordered according to the
HEALPix 'nested' scheme. This is a theoretically elegant scheme that
could speed up access to the data. That's the theory; in practice,
dealing with this is beyond horrible. I expect that all practical use of
the raw data will involve downloading the files and sorting them into
declination zones, similar to all UCACs and Ax.0 and B1.0. (Why ESA
didn't do that in the first place baffles me. I think someone fell in
love with the mathematical elegance of the HEALPix scheme.) Fortunately,
getting the data sorted into declination zones isn't all that difficult.

However, I expect most of us will _not_ be downloading 200 GBytes and
then keeping it on a half terabyte of hard drive. Instead, we'll just
download Gaia-DR1 data on an "as needed" basis for a given area, from
VizieR. I'll be setting up Guide to do that.

-- Bill

On 2016-10-11 16:17, Ted Blank tedblank@... [guide-user] wrote:
> Hi Bill, when you get a moment could you remind us what formats Guide expects for the UCAC one through four star designations?
> I cannot seem to find any specific examples in the Help files.
> Best regards,
> Ted Blank
> (603) 817 9814 (cell)
> Sent from my iPhone
> On Oct 11, 2016, at 3:00 PM, Bill Gray pluto@... <mailto:pluto@...> [guide-user] < <>> wrote:
>> Hi all,
>> The method Denis mentions will work, _if_ the URAT star is among
>> those displayed on-screen. For URAT1, Guide will extract only that
>> area from the binary catalog, expanding it into the ASCII file
>> 'urat.txt'. It is that file which Guide displays, using the TDF
>> (text definition file) system. And it's that file at which Guide
>> will look when you use Go To... Go to .TDF Object command.
>> I put in some extra code so that Go To... Object Name could recognize
>> UCAC-1 through 4 designations, and A1.0 and A2.0 and B1.0 designations,
>> whether the object was on-screen or not. I'll take another look at
>> getting URAT1 similarly recognized.
>> -- Bill
>> On 10/09/2016 03:03 PM, Denis boucherd@... <mailto:boucherd@...> [guide-user] wrote:
>> >
>> >
>> > Try under GO TO, Go To .TDF Object, select URAT1 in user database and
>> > press OK then enter the star number in search window.
>> >
>> > That should work.
>> >
>> > On 09-Oct-16 11:40 AM, stjohnrobinson@... <mailto:stjohnrobinson@...> [guide-user] wrote:
>> >> Hello Denis,
>> >>
>> >> I think you have misunderstood or I did not make myself clear enough.
>> >>
>> >> I have the URAT1 data set, and have configured Guide to display the
>> >> URAT1 stars successfully, what I am now trying to achieve is to
>> >> correctly format a search term that can be entered into the GOTO
>> >> command: -
>> >>
>> >> i.e 1URAT547-642315 this is a URAT1 star that guide will display,
>> >> amongst many others, however if you then enter the same format into
>> >> the GOTO command, it returns 'Not a valid object'.
>> >>
>> >> I have tried variations on a theme as it where but with out success.
>> >> So thanks for the response, I will have to see if Bill can enlighten me!!
>> >>
>> >> best regards
>> >> stjohn
>> >>
>> >
>> >
>> >
>> >