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This program can be much more than just a map of the night sky. Offhand, I can think of a whole bunch of things it can demonstrate. A couple of less-obvious ones are:

How the human mind sees patterns in what is actually random arrangements of points. (The constellations.)

That bright stars are less common than dim ones. (Because to be bright, a star has to be either unusually luminous or unusually close.)

Which pairs of stars rise or set at the same time depends on your latitude. (This is how the Polynesians navigated, I'm told.)

Some more obvious ones:

The earth rotates once in 24 hours. Which makes the sky appear to move at a rate of 15 degrees per hour from east to west.

The earth goes around the sun once in 365.242 days. Which makes the sky appear to move at a rate of about one degree per day from east to west.

The sun, the moon and the planets follow roughly the same path against the stars (the ecliptic), but they move at different rates. And because the earth goes around the sun, too, some planets appear to reverse direction at times.

Changing to a different longitude is like changing your clock.

Unless you're on the equator, some stars never set.

Davewa 16:07, 22 May 2008 (EDT)

Priorities for next release

I'd like to display the Milky Way outline on the full-sky chart.

The program is now set up for localization. I'm supplying EN (because that's what it was developed in) and ES (thanks to a translation by Daniel Castelo of Uruguay). Other languages would be nice.

-- Davewa 19:03, 25 March 2010 (UTC)

Constellations and Cultural History

Each culture has its own set of constellations and stories about how the sky and the universe was formed. StarChart can be used to introduce other cultures via their constellations and stories. And can be an adjunct to local cultural history. --User:AuntiMame 22 may 08 16:14

Developer's reply: Beta 4 has broken out the constellation table from the code. So in theory a local version of "" could be created to show the local culture's figures today. Of course, today nothing is labeled -- as was noted below, that needs to be changed, too. The constellation table organization would need a tweak to support adding a name and an abbreviation. The code would have to be modified to support this change to the structure of the data (presently simply an array of line segments; after the change an array of structures consisting of two strings and an array of line segments). This is all perfectly feasible to do.

But to create a local will require a local expert who both knows how to draw his culture's constellations and who knows enough Python to be able to successfully modify the data for the stick figures (each line of which requires specifying two equatorial coordinate values) and for the labels. Davewa 11:08, 23 May 2008 (EDT)

Further, if the constellations are "localized" to reflect the culture, the "Locate" and "Identify" features will break -- these features depend on having used the set of 88 IAU-defined constellations. (It's okay to localize the constellation names, though.) Davewa 18:34, 1 December 2008 (UTC)


This has now been implemented through the "Identify" feature.

Milky Way

What about a Milky way graphic kicking in at an appropriate brightness -- say about mag 4? With a dark sky this is a major orientation feature. Rmyers 17:27, 22 May 2008 (EDT)

Developer's reply: Living under severely light-polluted skies, I never even thought about that! But you're right. It's worth adding. -- Davewa 11:21, 23 May 2008 (EDT)

Low magnification points of interest

What about adding a layer with points of interest not visible with the unaided eye, but which can be seen with a small telescope or binoculars? M catalog objects, prominent double stars and the like. Rmyers 17:27, 22 May 2008 (EDT)

Developer's reply: That one's now implemented, mostly, in the Version 2.0 (rev 12) code.

I have added support for astronomy aided by binoculars. The activity now has the ability to zoom in on a 7-degree-square (well, round) area of the chart. I've provided a supplemental star catalog to magnitude 6.7 stars as well, but those will only display on the "detail" zoom level. The supplement adds another 2,500 stars and costs about three seconds of time when the chart re-draws. I think this is all the data it's safe to put in the catalogs. I also added a catalog of NGC objects for interesting binocular objects not covered in the Messier list, with emphasis on objects in the southern skies.

As for a smaller field of view, whereas that would support a telescope better my assumption is that any school which could provide a small telescope for an astronomy class could probably also have a better planetarium program on a more elaborate computer to use with it. (I use Cartes du Ciel, myself, for my astronomy -- it's free and you can download the source, but I'm not sure if it's FOSS, technically.) So I'd rather target naked-eye and binocular observers with this program and let the telescope-equipped find a better tool if they need one.

-- Davewa 22:24, 22 April 2010 (UTC)

The moons of Jupiter are binocular objects. Might it be worth adding the code to plot them in a magnified view when Jupiter is the object in the field? -- Davewa 13:08, 23 May 2008 (EDT)

Rmyers again:I agree that this shouldn't go too deep. I figure it should be centered as a naked eye guide. However, I also figure that a small 'spyglass' or pair of binoculars are fairly common even in quite undeveloped areas. I like the binocular field of vision guide idea. Rmyers 10:56, 24 May 2008 (EDT)

'Sky View'

I don't know if this is computationally feasible but...

What about a view that more closely resembles looking at the sky? Show a view from horizon to zenith looking in a specific direction with a view 90° (?) left and right. That is if someone is facing west he'd see from south to north, horizon to zenith -- more closely resembling his eye view. Panning left and right would change the direction of the center point.

In keeping with the education mission, this would assume less 'mapping' skills on the part of a young user. Mapping a flat sky chart to a hemispherical bowl over your head is not a simple task, particularly with objects near the horizon. This could give an alternative view with a less distorted view for objects lower in the sky. Rmyers 11:18, 23 May 2008 (EDT)

Developer's reply: I've seen this view in Cartes du Ciel and find the one that CdC provides to be harder (for me) to use than the whole-sky chart. The mapping of a quadrant of sky results in an onion-shaped figure that just looks weird to me. I don't know enough about mapping theory to produce a view of the sky which would look enough like what you actually see to be intuitive. My current mapping is pretty simple: azimuth maps to location around the circumference and altitude maps inversely to radius.

I find if you simply hold the XO so that the display is perpendicular to the ground and the direction you're facing is down then the map is pretty close to what you see from zero to 45 degrees altitude. Above 45 degrees, the best thing to do is lie down with your head facing north and hold the XO over your head with south at the bottom. -- Davewa 11:45, 23 May 2008 (EDT)


I found this site and they also have an Apple Dashboard widget. Starry Night Sky Chart. This is an 'online planetarium' similar to my sky view idea. Far slicker than is probably sensible ffor the XO, and the widget is essentially adware for their commercial products, but a good illustration of what I was thinking of. Too bad they aren't FOSS. Rmyers 16:29, 26 September 2008 (UTC)


Add the ability to advance time or change position to show what effect that has on the sky. A frame rate of around 3 per second should "feel" right for simple demonstrations, but a slower rate or the ability to manually step forward and backward through frames should also be provided. The "step by" should be under user control, too.

This ties into the demonstrating of how the sky moves, the "dance of the planets" and celestial navigation. (And it's just plain cool.) The animation isn't hard, but getting a good GUI to set up and control it can be. -- Davewa 13:05, 23 May 2008 (EDT)

I like this. A 'Planetarium' view. This plays nicely to your learn how the sky tells time and calendar concepts. How about a 'step by day' to show the passage of the seasons, not just accelerating time rate? Rmyers 10:56, 24 May 2008 (EDT)

Developer's Reply: I'd planned on step-by-hour, step-by-day, step-by-week, step-by-month and step-by-year. For position, I'd planned on step-by-degree and step-by-ten-degrees. -- Davewa 15:29, 26 May 2008 (EDT)

Locating Objects

This has now been implemented.

junior Astronomy 101 curriculum wanted

This is not directed at Dave, who has his hands full with coding StarChart, this is directed to those who are fans of StarChart. Picture StarChart bundled together with Moon and some good text content scraped from the NASA web-site (most govt website content is free of copyright as U.S. Govt. work) on galaxies, star formation, planets, etc. as an astronomy or physics classroom module. If you have good links in your favorites/bookmarks, please start collecting them over at Science#Astronomy. Cjl 02:19, 27 May 2008 (EDT)

Developer's Reply: This is exactly why I started this talk page. I wanted people to start thinking about ways to turn StarChart into a component of a course in astronomy for elementary-school students. -- Davewa 10:42, 27 May 2008 (EDT)

Another thing: now that the code has been reorganized, it's possible for someone to take the constellation table and (with some fairly simple plotting routines), create a "Constellations Flash-Cards" activity. This would display a constellation figure and a multiple-choice list of constellation names. The child would attempt to pick the correct name for the constellation. After some number of incorrect attempts (maybe 2 wrong tries out of five choices), the activity would show the correct name. An advanced version of this might for example also give the names of the brightest of the stars in the constellation. I'd do this myself, but I'm still a novice at Python and I don't yet know how to detect mouse clicks on the XO. Davewa 18:16, 12 August 2008 (UTC)

SW Versions

See the change log for details about what has been added or fixed at each release.


See reporting bugs for what bugs are known. Feel free to report bugs by editing that page as well.

Planned Features (not otherwise mentioned above)

  • Phase of the moon. If the moon is the target object when you click, show the approximate phase (New / 1Q / Full / 3Q)
  • Replacement of textual buttons with iconic buttons in most of the User Interface. Tooltips will be provided instead of textual labels.
  • Plot of visible ISS passes for that day. This may or may not be a separate activity, I'm still trying to decide if I want to add the extra complexity to StarChart or spawn a new activity that just plots the ISS on a constellation map. -- Davewa 20:09, 9 July 2009 (UTC)

Night Vision mode

Would it be a significant challenge to extend the switch from white-to-red to the top bar? cjl 19:04, 30 September 2008 (UTC) Developer reply: It might be; I'd have to see. For now, the work-around is to switch into full-screen mode (Alt+Enter) and hide the top bar entirely.



Congratulations on the new release. I'm looking forward to trying it out. Have you looked into doing the gettext thing to generate the POT file and getting this set up for localization as a Honey project on the Pootle server? It would be really great to give kids a chance to use StarChart in their native language. cjl 18:32, 1 March 2010 (UTC)

Thanks. I've done the gettext thing and created a POT file (and gotten a Spanish translation). This was included in the "version 11" release on 18 March 2010. -- Davewa 19:08, 25 March 2010 (UTC)

We'd be happy to host the PO file for StarChart on the Sugar Labs / OLPC Pootle server. Typically this involves having the code hosted in either the OLPC or the Sugar Labs git repositories (so that Pootle can be hooked in to commit PO files). Would that be an issue for you? It would give you access to many more localizers / languages if it were hosted in Pootle. cjl 22:52, 25 March 2010 (UTC)

Alt-Az Grids

How about adding altitude and azimuth grids, both equatorial and longitudinal. Since the FOV is not getting changed, it should be a matter of drawing some static arcs.

Developer's Reply: The alt/az grid is static but the ra/dec grid isn't -- the location of ra changes with time. And with the magnfication feature the FOV is no longer constant, either.

-- Davewa 22:26, 22 April 2010 (UTC)