Interface Description

ESASky is an exploration style interface where the entire sky is available to search and explore. Its functionalities are described below:



esasky modes and basic exploration functionalities

New to version 3.0, you can select the mode in which you want to work: Science mode or Explorer Mode. This can be done in the welcome dialog window or with the switch on the top bar:

Science mode includes all access to science ready data, skies, publications and the observations planning tool whilst the Explorer mode allows users to explore the sky in different wavelengths, explore example target lists and roll the dice to explore different astronomical objects.

Since version 3.1, you can also choose the language in the drop-down menu on the top bar (English, Spanish and Mandarin available for now):

The coordinate frame can be changed with the drop-down menu on the top right corner. Next to it, the cursor coordinates (or the coordinates of the centre of the field-of-view, in blue, if the mouse is outside the window), the size of the field-of-view (in the format RAxDEC) and the name of the displayed HiPS all-sky map are also indicated on the top bar. When in the equatorial system, clicking on the coordinates in the header will change the format back and forth from sexagesimal to decimal. If the data panel is open, this switch is also reflected in the results tables.

Pan around the sky with your mouse and zoom in and out of the sky with the scroll button of your mouse or with the +/- buttons:

There is also the possibility to overlay/hide a coordinate grid by clicking on the corresponding button on the top bar:

Right clicking anywhere in the sky will bring up the below menu, where you can search the selected coordinates for objects in SIMBAD (currently set to a 5 arcsecond radius), NED (currently set to a 2 arcminute radius), VizieR, the VizieR Photometry tool (currently set to a 5 arcsecond radius), and the World Wide Telescope.  All these default search radii will be adjustable by the user in future versions. From this menu there is also access to the help documentation and the ESDC helpdesk:



The search field is located in the top right of the interface and accepts coordinates or an object name that can be resolved by SIMBAD. Both equatorial or galactic coordinates are accepted. By default the search is in the equatorial (J2000) system; to input galactic coordinates, the 'galactic' frame must be selected in the top-left corner of the application. Simply type the name, or coordinates, and ESASky centres on this region of the sky. The region displayed is chosen by taking the size of the object from SIMBAD.

It is also possible to enter an author's name or a bibcode. In this case, the user gets a list of all the SIMBAD sources related to that author's publications (and a table with those publications) or to the publication associated with that bibcode, respectively (go to the description of the Publications Search feature for more details).

See here for the list of accepted search formats.



The top left of the interface shows the coordinates of the cursor, the coordinate system, Equatorial (J2000) or Galactic, the field of view (FoV), the sky that is currently being displayed, and below this, a line of buttons. The first to the left is the skies icon:

Clicking on the icon brings up the Skies menu. The skies are ordered into wavelength regions, from Gamma-ray to Radio, and an Others section at the bottom which currently holds physical models. Select a sky by choosing the wavelength region in the first panel, and browse the skies in the second panel. Details on each sky can be found by clicking the i icon. For further details and a list of all the available skies, go to the skies (HiPS) information page.


The colour of the skies can be modified with the colour map options 'Native', 'EOSB', 'Planck', 'Rainbow', 'Greyscale' and 'Cubehelix'.

A sky can be added to the stack by selecting the + button:

Click on the video style buttons to play through the skies in the stack, skip forward, backwards or stop.

Since version 3.2, you can also move between skies using the slider:


DATA PANEL (Imaging, Catalogue and Spectra Search)

To search for imaging, catalogues or spectral data (and to open the data panel) click on the respective imaging, catalogue and spectra icons in the left menu. The numbers correspond to the number of imaging data, catalogue sources and spectral data that are available for the region of the sky displayed in the browser (not just for the searched target):

Clicking on one of the menus brings up a treemap which shows the imaging catalogues or spectral data for each mission. The size of the boxes within the treemap are proportional to the number of observations available, with the largest box always appearing in the top left. The wavelength regions are included with the mission names and the missions, the majority of the time, are colour coded by wavelength, with Gamma, X-ray & UV appearing blue or purple; Optical appearing green; and IR to Radio appearing orange and red. As said above, these results are for the entire area being displayed, not just for the source. The results being shown are the highest level science observations only.


The treemaps are interactive, use the slider at the bottom to select a wavelength range, the available missions in the given range are then shown. Click on each mission to query the archives and load either the images, catalogues or spectra for the region, depending on the treemap selected. A results table appears with the observation or catalogue details and the footprints of the observations or catalogue sources are drawn on the sky. Clicking on an observation or catalogue source will highlight the corresponding observation footprint or source in the sky, and vice versa:

The colours and thickness of the contour lines of imaging and spectroscopic footprints can be changed by clicking on the "Customise" button to the left of the data table (the colour of the circle will match that of the footprints): 

Also the shape and colour of the symbols showing the positions of catalogue sources can be modified using this functionality.

If a catalogue contains proper motion information, ESASky displays not only the position of the sources as defined in the catalogue, but also the direction of motion. In a large field of view, this is shown with a dotted line; the length of the line is proportional to the total proper motion value, but it does not represent the precise movement. The colour and length of this line can be customised by the user.

Once you zoom in, the dotted line is replaced by an arrow showing the motion of the source between the catalogue's reference epoch (indicated in the labels of the RA and Dec columns in the data table) and J2000. For example, in the case of Hipparcos, the arrow starts in J1991.25 and ends in J2000; while in the case of Gaia DR2, the arrow starts in J2000 and ends in J2015.5. In both cases, the square represents the original catalogue position (J1991.25 for Hipparcos and J2015.5 for Gaia). Clicking on the Customise button, it is possible to change the colour of the arrow (but not its length), and to subtract the mean or the median of the proper motions of all the stars in the field of view.

Columns in a table can be sorted by clicking on the column's header, and filtered using the funnel button:

It is possible to filter on strings, numerical values and dates. With strings, users can concatenate more than one condition in the same filter with the "|" symbol, which represents the logical OR. With numbers, it is also possible to set a range of numerical values, either with the slider or manually entering the upper and lower values. When a column has been filtered, the funnel button is highlighted in red, and the number of rows displayed after filtering is displayed at the bottom of the screen.



Clicking on the search icon of each row will retrieve the observation postcard directly from the corresponding mission archive:

Clicking on the SAMP button will send the corresponding image to a SAMP (Simple Application Messaging Protocol) enabled application (e.g. DS9, Aladin):

Finally, within the results table, each observation or source can be centred on by clicking the 'Centre on observation' or 'Centre on source' button:

To download the observations, tick the left boxes (or the top left box to select all observations), click the 'Download' button (located to the left of the data panel) and choose 'Download data products'.

The Download menu also provides the option to save the results table in CSV or VOTable format. The results table can also be sent via SAMP to a SAMP enabled application (e.g. TOPCAT) by clicking the SAMP button in the left menu . The top icon in the left menu of the data panel is to refresh the mission/tab data . For example, if you zoom out or pan to a different part of the sky, you can reload the mission/catalogue data for the displayed region by clicking the refresh icon. Also, if you have panned to another region or performed another search, you can go back to the tab's original search field by clicking on the 'recentre' icon in the left menu: .

To visualise the sky coverage of all the available ESA missions, zoom out to a distance where the treemap is showing that thousands of observations are available (or zoom out to view half the sky) and then click on one of the missions. A message will appear showing the total amount of objects (observations or sources) in the field of view. If this is below 10 million, then filtering on the data can be performed. The coverage maps are interactive, a pop-up window will appear when a 'tile' in the sky is selected with information on the number of objects available in the tile region per loaded mission. If the objects are below a certain threshold the data can be loaded in the region of the selected tile by clicking on 'load data'. Zooming in will automatically load the footprints and metadata once below a certain number of objects.

The image below shows coverage maps for XMM-Newton X-ray (imaging; purple), Chandra X-ray (imaging; purple), Hubble Space Telescope Near-IR, Optical and UV (imaging; light green, green and light blue respectively), Herschel far-IR to submm (imaging; red) and Spitzer Space Telescop mid to far-IR (orange). As with the footprints, the colours of the coverages are customisable.



In ESASky, you can search for any planet, satellite or comet observed by HST, Herschel and XMM-Newton (targeted or serendipitous images). Type the name or ID number of the object in the search box and a selection of suggested targets will be given:

Choose the target and the solar system icon will be activated with the number of available imaging observations and the treemap will open:

Select the mission and all available imaging observations will load in the data panel and the footprints will be drawn on the sky. Additionally, the orbit of the solar system object for the entire duration of the mission will be plotted:


For this feature, the ESASky team has created a pipeline that takes the ephemeris information of each SSO with respect to the position of each spacecraft using software by the IMCCE (Institute of Celestial Mechanica and Ephemeris Calculations, Paris) and performs a crossmatch on the SSO orbits against the entire mission archives to find observations in which the SSO fell within the imaging instrument's field of view during the time the images were being taken.

Asteroids and other solar system objects will be added in the next minor version of ESASky, and imaging observations from other missions will also be added soon.  

This short movie shows the SSO feature in action.



In ESASky, you can now search for SIMBAD sources with scientific publications from the Smithsonian/NASA Astrophysics Data System (ADS). The publications tool has it's own button (an academic hat): 

Once the icon is selected, the sources containing publications are shown (with a yellow and red icon) in the displayed field of view. The display can be updated automatically when changing the field-of-view by selecting the "Update on move" option. It can also be updated manually with the "Refresh" button.

If the number of sources is very high, the list will be truncated (by default) to the 3000 sources with highest number of publications. This can be customised by clicking on "Settings" and playing with the available options. The "Refresh" button next to the slider will reset to the default values.

Clicking on each source loads a table with the publications for that object, including a link to the paper in ADS, the title, authors, journal and date. The first column contains a button to load the sources from each individual paper (obtained from SIMBAD):

The sources are loaded into a target list and can be browsed through, object by object, to visualise them on the sky.

To deactivate the publications tool, click again on the publications icon. Please note that we currently have a limit of 3000 on the number of papers per source that can be displayed and sorted in the results table:


It is also possible to search for publications by author or bibcode, simply entering it in the search field (go here to see the formats). If an author's name is entered, a table will open with the author's publications that are linked to sources in SIMBAD, and the list of sources will be uploaded. Entering a bibcode, the list of related sources in SIMBAD will be uploaded.



Since version 3.2, it is possible to query data from external data centres via their Table Access Protocol (TAP) services compliant with Virtual Observatory standards. For now, this possibility is limited to the data provided by the European Southern Observatory (ESO), the Canadian Astronomy Data Centre (CADC) and the Mikulski Archive for Space Telescopes (MAST) in their TAP servers, including images, spectra, data cubes and time series data. It must be noted that these data, contrary to those offered via the images, spectra and catalogues functionalities, have not been curated by the ESASky team. We plan to expand this functionality to include data from any external TAP of the user's choice. 



To use this functionality, click on the External Data Centre button:

This will open a treemap showing the servers with data available in the visualised region. Clicking on any server, the treemap will display the types of data products available:

Clicking on any data product will display the data collections available:

It is possible to change back to the previous treemap level with the "Back" button or to filter the missions/telescopes by wavelength using the slider at the bottom of the treemap:

Clicking on a collection, the corresponding metadata table will open in the data panel, and the footprints will be displayed on the sky. The table can be browsed, filtered, resized and downloaded in the usual way. To download a particular data product, click on the corresponding download button in the "Access Url" column:

A window will pop-up with information on the files available in the server for this product, which can be downloaded by clicking on the corresponding link.



Next to the solar systems icon in the top left menu is the 'upload target list' icon: 

You can choose to either select a predefined target list, grouped by type of object:

or you can upload you own text file containing your list of targets, either names resolved by SIMBAD or a list of coordinates. While the list is loading, the message 'Resolving target list...' appears at the top of the interface, then once loaded, the target list appears on the left. Click on a target to view it in the sky. If an object has not been resolved by SIMBAD it will be crossed out. Below the target list are some video style buttons, press play to play through the list of targets, the target being displayed will be highlighted in dark grey in the list. Text and comments can also be added to a target list and the text is displayed in ESASky in a separate window. See here for the format needed to display text and some example files.



The observations planning tool icon lies in the top left menu, next to the target list icon: 

This tool projects onto the sky the footprints of astronomical instruments, at any chosen position and orientation, and has been developed to aid professional astronomers when they are defining their future observation proposals for a particular space mission or ground-based telescope. Currently the tool works for all the James Webb Space Telescope (JWST) instruments, including being able to project the full focal plane of the JWST. The possibility to project the footprints of other live missions, like XMM-Newton or HST, will be implemented in the near future.

IMPORTANT: This functionality is not intended to replace the JWST ATP tool, but just to provide a quick-look aid for astronomers planning JWST observations that require overlapping with existing observations by other missions available in ESASky, or who want to make sure that their instrument or parallel pointings are covering/avoiding particular features or objects in their target regions. The coordinates and positional angles of the pointings defined using this functionality have to be checked and refined in the APT, which is the official tool for preparing JWST observations. For information and installation of the APT, go to this STSci webpage; for details on the different JWST instruments, click here.

ESASky uses the latest version of the JWST SIAF (version number shown in the bottom of the planning tool window from ESASky v3.5 onwards). The SIAF is a reference file used in operations that contains the official information on all apertures (e.g., NIRCam Apertures) and internal instrument coordinates. The JWST Project Reference Database serves as the repository for operations reference files like the SIAF, its version number is a unique identifier of the reference files that it bundles. APT prompts the PRD version number used for observations preparation, see here for further information. 

Clicking on the icon opens the observations planning window, and clicking on the plus '+' opens the instruments menu:

When an instrument is selected, the corresponding footprint aperture is displayed in the centre of the field of view. You can change the location and orientation of the aperture with the arrows, or by typing into the fields. The rotation (APA, or aperture position angle) is the angle specific to the instrument field of view (in degrees), regardless of its offset angle relative to the Observatory V3 axis. This parameter is used to specify the desired orientation of a JWST aperture using the APT special requirements, see here for more information. When the footprint is in the correct position, click on the 'Copy coordinates and data' to get the pointing coordinates and position angle. 

By default, each instrument's aperture has a predefined centre. However, it is possible to centre it in a particular aperture by choosing it in the menu:

Clicking on the apertures centres will display a tooltip with the positional information of that centre:

It is possible to display several footprints of the same or different instruments together, and to move and orientate each one of them individually. In case you are planning simultaneous observations with several JWST instruments, there is also the possibility to display and position the full focal plane at once. To do this, check the 'All Instruments' option beside the detector menu. The footprints of all instruments will be displayed with the correct relative positions and distances on the JWST focal plane. Your selected instrument will be shown in red and the other instruments in green.

See also the following video: How to plan future JWST observations



In the top menu, on the right, lies the snapshot icon: 

Click on this icon to take a screenshot of your displayed ESASky screen (including any observational footprints and catalogues also displayed on the screen) and save it as a png file. A number of your png files can then, for example, be combined into an animated gif (note: locally on your computer, not currently with ESASky). The following animated gif shows M31 in Soft X-Rays (XMM-Newton EPIC color), Optical (DSS2 color), Mid-infrared (AllWISE color), Far-infrared (Herschel PACS RGB 70+160), Submillimetre (Herschel SPIRE RGB 250+350+500) and Radio (NVSS intensity maps), with the Gaia DR1 TGAS (orange squares) and XMM-slew (light blue squares) catalogue sources:



Roll the dice and take a tour through the cosmos! In explorer mode, click on our explore random target icon (dice icon) and enjoy discovering and reading about different types of astronomical objects in the sky.

Found your own amazing sources in ESASky? Tell us here and we'll add them to the list!


BOOKMARK / Sharing

By clicking on the bookmark / sharing icon on the top bar, the URL of ESASky is copied onto your computer's clipboard. This URL contains information on the target/coordinates, the background sky, the field of view, and coordinates frame. When copied into a new tab, ESASky loads on exactly the same coordinates, with the same background sky, field of view and coordinates frame. This link can then be shared, for example, via social media or with collaborators, to share interesting objects or regions of the sky.  Below are some examples of the bookmarks feature:

The sky (HiPS) name must be the one appearing in the ESASky skies menu. The target name will be resolved by SIMBAD.


AdditionaL Information and HELP MENUs

There are two buttons on the top bar for help and additional information: The first, a question mark, links directly to the 'How to' page. The second, "Feedback", gives access to the ESASky Userecho community. The last button on the right corner brings up a menu with other help and information resources, as well as a link to the World Wide Telescope.