Skychart

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====== GAIA DR3 ======
==== GAIA DR3 is now available and can be used with Skychart  ====
{{ :en:news:cdc_gaiadr3.jpg?350|M13 with GAIA DR3}}

The Gaia Data Release 3, consist of astrometry, photometry, radial velocities, astrophysical parameters and variability information for about 1.8 billion sources brighter than magnitude 21.\\
You can read more detail about GAIA DR3 in the [[https://www.cosmos.esa.int/web/gaia-users/archive|release documentation]]

The data used by Skychart are very similar to what was already available in [[GAIA EDR3]] but the file organization for the magnitude 18 and 21 part allow a much faster access and chart drawing.\\
A new small file with stars to magnitude 12 is intended to replace the use of Tycho-2 in Skychart.

Another specific difference for Skychart is a better integration with Hipparcos data for the bright stars when using the default "Gaia-Hipparcos" catalog.\\
Now the astrometric data are from GAIA for the bright stars with cross identification between GAIA and Hipparcos. Also the GAIA magnitude are added.\\
A flag show in the [[en:documentation:detailed_information|detailed information]] allow to know the origin of the astrometric data:
  *0: all astrometry from Gaia
  *1: radial velocity from XHIP
  *2: parallax from Hipparcos
  *4: proper motion from Hipparcos
  *8: rejected match for position error > 5"
  *16: rejected match for V error > 2
  *32: no proper motion, position is HIP 1991.25
  *64: no match, all astrometry is from Hipparcos

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====Use with Skychart====

===Use a catalog prepared for Skychart===

You can download this full catalog for local offline use.\\
This require a version of **Skychart higher than 4.3-4701**

Start Skychart and use the menu Update / Install object catalog:
{{:en:news:install_gaia_dr3.png|Install GAIA DR3}}

The files are split in four parts of increasing magnitude so you can limit your download size.\\
It is mandatory to install the lower parts, you cannot install only Part 2 without Part 1. \\
But you can install only the small Part 1 if the magnitude 12 is sufficient for you.

The big Part 3 and 4 are split in smaller files of 1 GB. This allow to interrupt the installation after one of this file is complete to restart later.

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 DR3 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.

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===Online catalog===

You can use the GAIA DR3 data with Skychart without installing anything by using the [[en:documentation:catalog#vo_catalog|VO catalog]] feature.

Make a chart in Eq projection with a FOV of 10-15 arc minutes in the area of interest.\\
Open the Catalog settings.

Click Add in the VO catalog tab and search for Gaia DR3, select the catalog I/355, click Select catalog.

Select the first tab I/355/gaiadr3, enter the default magnitude: 21, for "Name" select DR3Name, click Download catalog.

Make sure the GAIA DR3 row is green and click the OK button.\\
If no star are show be sure in menu "Chart/Show Objects" that "Show stars" and "Show Virtual Observatory data" are checked.\\
You can return to the screen later to load the data for a new area with a click on the arrow in the Reload column.

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===Note about the star magnitudes===

GAIA use its own [[https://www.cosmos.esa.int/web/gaia/dr3-passbands|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://gea.esac.esa.int/archive/documentation/GDR3/Data_processing/chap_cu5pho/cu5pho_sec_photSystem/cu5pho_ssec_photRelations.html|GAIA documentation]]. The star diameter on the chart is relative to the G magnitude.\\

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