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--- en:news:gaia_dr2 [2018/06/10 18:38] – created pch
+++ en:news:gaia_dr2 [2019/07/17 12:47] (current) – pch
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 DR2 sky coverage is now very good and this catalog can be use for general star chart. But many bright stars are missing so you must use it along with the default Hipparcos catalog.
-You can read more detail about GAIA DR2 in the [[http://gea.esac.esa.int/archive/documentation/GDR2/index.html|release documentation]]
+You can read more detail about GAIA DR2 in the [[http://gea.esac.esa.int/archive/documentation/index.html|release documentation]]
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@@ Line 36: / Line 36: @@
 You can download this full catalog for local offline use.\\
 This catalog include the following fields: source_id, ra, dec, phot_g_mean_mag, phot_bp_mean_mag, phot_rp_mean_mag, pmra, pmdec, parallax, radial_velocity.\\
-You can search by source_id using the format: Gaia DR2 1328053954366555648
+You can search by source_id using the format: Gaia DR2 1328053954366555648\\
+The Vizier link at the bottom of the [[en:documentation:detailed information]] window give you access to all the other Gaia data for the selected star.
-This catalog format require you use a version of Skychart higher than 4.1.1-3736. Do not try with a previous version, this result in totally wrong name, proper motion and parallax.
+This catalog format require you use a [[https://sourceforge.net/projects/skychart/files/0-beta/|version of Skychart higher than 4.1.1-3736]]. Do not try with a previous version, this result in totally wrong name, proper motion and parallax.
 The files are split in three parts of increasing magnitude so you can limit your download size.\\
@@ Line 47: / Line 48: @@
   * [[https://sourceforge.net/projects/skychart/files/2-catalogs/Stars/GAIA/gaia-dr2-3.torrent/download|gaia-dr2-3.torrent]] : The remaining stars from magnitude 18 to about 21, download size 36.4GB
-For convenience you can also download the first part, equivalent of gaia-dr2-1.torrent, directly from your browser: [[https://sourceforge.net/projects/skychart/files/2-catalogs/Stars/GAIA/gaia1.rar/download|gaia1.rar]], size 1.1 GB.
+For convenience you can also download the files from your browser using http, but this is likely to take more time and is less reliable than the torrent: [[https://vega.ap-i.net/pub/GaiaDR2/]]
-Extract all the 3 parts on the same directory, preferably in your Documents folder. This make the following folders:\\
+Extract all the 3 parts on the same directory, preferably in your Documents folder. On Windows you can use [[https://www.7-zip.org/|7-zip]], on Linux use "''unrar x gaia*.rar''". This make the following folders:\\
 .../gaia/gaia1\\
 .../gaia/gaia2\\
@@ Line 55: / Line 56: @@
 From Skychart, menu Setup/Catalog check Gaia and indicate the full path for .../gaia/ , not for any of the sub-directories.
+{{:en:news:cat-gaia.png?350|}}
 As the first part do not include the know Hipparcos stars to avoid duplicate plot of the bright stars you must also check Hipparcos at the same time as Gaia to add the bright stars.
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 They not include the star name, the proper motion, the parallax and the radial velocity. This is the price for the compactness but this values are not mandatory to make a nice star chart.
-The download size is much smaller, between 300MB and 840MB, see:\\
+The download size is much smaller, between 300MB and 1GB, see:\\
-https://sourceforge.net/projects/astap-program/files/star_databases/
+https://sourceforge.net/projects/hnsky/files/star_databases/
 Extract the files in your HNSKY directory or in any other folder.\\
-From Skychart, open the menu "Setup/Catalog/Other software data".\\
+From Skychart (version 4.1.1-3707 and up), open the menu "Setup/Catalog/Other software data".\\
 Indicate the path where you extract the files, check to use the HNSKY database, enter the mini and maxi FOV number as for the other catalog, and select the database to use if you have more than one at the same location.
+----
+===Note about the star magnitudes===
+GAIA use its own [[https://www.cosmos.esa.int/web/gaia/iow_20180316|specific passbands]] for the star magnitude.\\
+On a first approximation you can imagine G as equivalent to unfiltered CCD, BP as the full visual range (B+V+R), and RP as the I near infrared.\\
+The Skychart catalog show this three magnitudes and in addition it compute a V magnitude and a B-V color index using the relation given in the [[https://doi.org/10.1051/0004-6361/201832756|GAIA documentation]]. The star diameter on the chart is relative to the G magnitude.\\
+The HNSKY database G16 use the V magnitude and show the BP-RP color index as well as B-V computed using the same relation. G17 and G18 use the BP magnitude.
+----
+Do you get enough stars now?
+{{:en:news:cdc_5146_gaiadr2.jpg|}}