Astro Mosaic Telescope Planner


Link to AstroMosaic page.


Source code in GitHub.



Astro Mosaic is a tool for planning telescope observations. It shows a visual view of the target using a selected telescope, visibility during the night and it can calculate mosaic coordinates.

Tool includes

Multiple telescope services

Currently Astro Mosaic supports Telescope Live, Slooh, RoboScopes, SkyGems, Hubble and James Webb Space Telescope (JWST) telescopes. You can also add your own telescope (see page Astro Mosaic Configuration).

Direct links to telescope services are below.

Add own telescope

Own telescope can be added to Astro Mosaic with Add telescope option. Telescope information includes telescope field of view and location. Telescopes added with Add telescope option are not persistent so they disappear when Astro Mosaic is restarted. For other option to add your own telescope see a separate document Astro Mosaic Configuration.

Telescope field of view

AstroMosaic can show telescope field of view and mosaic grid view.

Night and year visibility

AstroMosaic can show target altitude for a given night and also midnight altitude for next 12 months. Optionally it is possible to show target azimuth. Also moon altitude, phase and distance from the target is shown.

Target altitude and moon altitude.

Target altitude and moon altitude at midnight for the next 12 months.

Target altitude, azimuth and moon altitude.

Multiple catalogs

Astro Mosaic supports the following catalogs.

All catalog object names are added as a catalog layer to the map view. Each catalog object name is written next to that object on a map to make it easier to identify major objects in a map. Catalog map layers are disabled by default.

There are a total of 13959 NGC and IC objects that can be shown on the map. The Sharpless catalog has 313 objects listed mostly from the northern hemisphere. The RCW catalog has 182 objects listed mostly from the southern hemisphere. RCW catalog also includes objects from the Gum catalog.

Catalog object markers are clickable. When you click on a marker a short info is written on the panel to the right side of the map. If the Wiki check box is checked then the Wikipedia page of that object is shown when possible.

Filtering in catalog list

It is possible to filter catalog lists in a few ways.

Filtering points are calculated at midnight and then two and four hours before and after midnight. So in some cases it is possible that a target is not listed if it will match the filter only between those calculated points.

Sorting catalog list

It is possible to sort catalog lists by altitude when altitude filter is enabled. It should help finding those targets that have the best visibility ate selected time.

Panel view of catalog

Panel view shows 25 first catalog objects as separate panels. It allows an easy visual view to targets with the chosen telescope.

Controls on the map

Visual reposition of the target

Reposition mode can be used to visually move current framing using the mouse. Reposition mode can be chosen by checking the Reposition box in the interface.

Reposition is useful also when searching for targets in the sky map. It is possible to center to the current Aladin view position by checking the Reposition box and moving the image with the mouse. Note that if you have moved far away from the original position you need to click the Refresh button to update visibility charts.


It is possible to add one or more marker to the view by preceding coordinates with a special keyword marker. Markers work only with ra/dec coordinate list and cannot be the first entry in the list.

Example of a target with a marked added: d 338.8958 39.4908, marker 22:35:52.28275 +39:38:03.5868,marker%2022:39:15.67864%20+39:03:00.9712&telescope=SPA-1

Configuring Astro Mosaic

Configuring Astro Mosaic using URL parameters is described in a document Astro Mosaic Configuration. It is possible for example to add your own camera and lens or telescope to Astro Mosaic.

Embedding Astro Mosaic

Embedding Astro Mosaic to a page is described in a document Astro Mosaic Configuration. It is possible to embed parts of Astro Mosaic in an Iframe by calling AstroMosaic.html with URL parameters or in a user given div section by loading script file AstroMosaicEngine.js and calling function AstroMosaicEngine.

Aladin API for visual view of target

Astro Mosaic would not be possible without Aladin Sky Atlas and Aladin Lite. Aladin Sky Atlas is a great interactive map created from digitized astronomical images. It is simply amazing that such a great resource is available. And it is totally free!

Aladin Lite provides HTML5 and programmable Javascript API interface to Aladin Sky Atlas. It makes it very easy to integrate into a web page. There are great examples and documentation to get started very quickly.

For displaying images Aladin Lite uses preprocessed data from HiPS. HiPS (Hierarchical Progressive Surveys) is the hierarchical tiling mechanism which allows users to access, visualize and browse seamlessly image, catalogue and cube data. There is 250TB of data available from different HiPS surveys.

Sesame Name Resolver

Astro Mosaic uses Sesame service for resolving names. When a name like m101 is written into the target input box, a query is sent to the Sesame server to resolve the name. As a result Sesame server will return an XML page that contains target RA/DEC coordinates among other things. Sesame is actually an interface to other name resolvers: Simbad, NED and VizierR.

Calculating position of sun, moon and planets

There are very good resources available to calculate sun, moon and planet positions at a certain time and place. In Astro Mosaic that information is used to calculate for example moon position and altitude during the night, sun rise and set times and moon phase.

Perhaps the best resource is a page How to compute planetary positions written by Paul Schlyter. It has a lot of good and practical information. He has also another page Computing planetary positions - a tutorial with worked examples that has similar information. Those pages have all required information on orbital elements, coordinate transformations and such.

Moon phase

Moon phase shown in Astro Mosaic is based on it's own calculations so it may not be exactly correct. It was very difficult to find a good example of that so Astro Mosaic just calculates the angle between sun and moon as seen from earth. That angle is then used to calculate moon phase.

When the moon and sun are on the same side angle is zero degrees and moon phase is 0%, when they are on opposite sides the moon phase is 100% and when angle is 90 degrees phase is 50%. And other vales are between those.

Wiki interface

Astro Mosaic can optionally show a Wiki page of the target. Wikipedia has an API that can be used to find a page id based on a search text. A surprisingly large number of Messier, NGC and IC targets has its own page at Wikipedia. If a page id is found then a mobile version of that page is shown in its own frame.

Astro Mosaic does some basic parsing on names before they are sent to Wikipedia search. For example messier objects can be written as m101 but they are translated to Messier 101. Also NGC and IC objects are formatted slightly before sending to Wikipedia.


Sometimes in 2018, very early in my astrophotography hobby, I wanted to image Western Veil Nebula. It did not fit into the telescope field of view so I started working on a three panel mosaic. I used Stellarium to approximately find correct coordinates. I managed to get the mosaic done but it was a very random process. I started to look for some tools to calculate mosaic coordinates but failed to find any free ones. So I decided to learn something new and do the coordinate calculations myself. I did the first version in Python but soon found out about Aladin Sky Atlas. With that I could do even better and see the actual framing on the sky atlas on a web page. After that I have added more functionality like visibility charts and different catalogs for finding targets.