Siril image annotations (documentation for version 1.2)

View of full annotated image

View of full annotated image

Annotations are glyphs displayed on top of images to depict the presence of known sky objects, like galaxies, bright stars and so on. They come from catalogues but can only be displayed on images for which we know which part of the sky they represent, images that have been plate solved and contain the world coordinate system (WCS) information in their header, so only FITS or Astro-TIFF files. Plate solving, can be done within Siril in the Image Information menu, Image Plate Solver... entry, or using external tools like astrometry.net or ASTAP .

Buttons for annotations

Buttons for annotations

When a plate solved image is loaded in Siril, you can see the sky coordinates for the pixel under the mouse pointer displayed at the bottom right corner and the buttons related to annotations become available. The first button activates object annotations, the second the celestial grid and the compass.

Types of catalogues

Siril comes with a predefined list of catalogues for annotations:

  • Messier catalogue (M)
  • New General Catalogue (NGC)
  • Index Catalogue (IC)
  • Lynds Catalogue of Dark Nebulae (LdN)
  • Sharpless Catalogue (Sh2)
  • Star Catalogue (3661 of the brightest stars)

In addition, 2 user defined catalogues can be used:

  • User Deep Sky Objects Catalogue
  • User Solar System Objects Catalogue

Catalogue management

Both these catalogues can be enabled/disabled for display in the Preferences menu, Astrometry tab.

A slider on the right side, allows you to easily navigate across the catalogue list.

Catalogue management in Preferences/Astrometry

Catalogue management in Preferences/Astrometry

The two user defined catalogues can also be purged (ie deleted) via the appropriate buttons.

The user catalogues (DSO, SSO or extra catalogues) are stored in the user settings directory and can be easily modified.

Their location depends on the operating system:

  • for Unix-based OS they will be in ~/.config/siril/catalogue
  • on Windows they are in %LOCALAPPDATA%\siril\catalogue.

The position of the compass on the image can be adjusted from the preferences too.

These annotation catalogues are for display purposes only. They are not used in astrometry or photometry tools, contrary to the star catalogues like NOMAD, which can now be installed locally too.

Local Catalogue (NOMAD) setup

Local Catalogue (NOMAD) setup

Searching for a new object

When the name of an object in the image is known (if not, see the “The inverse search” section), it is possible to add it to annotations:

  • with the image loaded and plate solved, type <CTRL> <SHIFT> </>or Search in the pop-up menu (right click).

A small search dialog will appear. In it, object names can be entered, then pressing <ENTER> will send an online request to SIMBAD (for a star of Deep Sky Object) to get the coordinates of an object with such a name. If found, and not already in any catalogue, the object will be added to the Deep Sky user Catalogue.

The items of this catalogue are displayed in ORANGE while the objects from the predefined catalogues are displayed in GREEN.

Deep sky objects from user and predefined catalogues

Deep sky objects from user and predefined catalogues

From Siril version 1.2, we can now search for solar system objects too, using the Miriade ephemcc service. This is done by prefixing the name of the object to be searched by some keyword representing the type of object: a: for asteroids, c: for comets, p: for planets. Since they are moving objects, they can be added several times, and the request is done for the date of observation of the currently loaded image. The date is associated to the name in the user Solar System Catalogue. The items of this catalogue are displayed in YELLOW.

Examples of valid inputs (not case sensitive):

  • HD 86574 or HD86574 are both valid for this star
  • c:67p or c:C/2017 T2 are valid forms for comets
  • a:1 and a:ceres are both valid for (1) Ceres
  • a:2000 BY4 is valid for 103516 2000 BY4
  • p:4 or p:mars for Mars

Filling a Solar System user Catalogue: which SSO is in this field?

As previously said, solar system objects are moving, so, in order to get them displayed in a plate solved image, Siril has to request a particular online server of the IMCCE (SkyBoT ). To answer the question Is there any solar system object in my image?, a special function gives (and show) you the answer:

  • with the image loaded and plate solved, right click/Solar System Objects, or in the command line you can use the solsys function.

It displays in RED all the Solar System objects in the field of view (if any, of course).

Additional information is available in the console (such as the magnitude, RA and Dec).

These red annotations will be erased as soon as the Show Objects names button is toggled.

Result of a Search Solar System process

Result of a Search Solar System process

However, you may want to save any particular item in the User Solar System Objects Catalogue. It can be done by using the Search command for a solar system object as previously described.

This way, the saved item is diplayed in YELLOW.

View with predefined/DSO/SSO

View with predefined/DSO/SSO

The inverse search: what is this object?

Especially useful for photometry works, it is possible to identify a star or other objects in the image by drawing a selection around them, right clicking to bring up the context menu, and selecting the PSF entry. This will open the PSF window, and if it’s a star it will display the Gaussian fit parameters, but it will also display a Web link at the bottom left of the window: opening it will bring you to the SIMBAD page for the coordinates of the object and in many cases will give you the name of the object. SIMBAD doesn’t have all known objects, but the coordinates from the page can still be used as a starting point to look for the object in other online catalogues, for example Gaia DR3 (VizieR) .

Extra catalogues

Sometimes, users create their own catalogues, we can try to link them here to help everybody. They are user catalogues, so installing them requires either replacing the current user catalogue, or by manually merging their lines into a new file.

List of known user catalogues: