Sunday, May 22, 2016

Asterisms interactive and with location/time setting

Since my interactive celestial map is working fine now, it makes sense to change the previously static asterisms map to an interactive display. It now has the possibility to select asterisms by average brightness, optionally show constellations and guiding lines between the brightest stars, and limit the display of stars by magnitude. The latter will also make the sky background grayer and let the Milky Way band vanish into the mist to simulate the effect of light pollution.

A completely new feature for the celestial map is the selection of local coordinates and date/time, which will display the current sky above the chosen location. The "Here" and "Now" functions set the respective fields to the local coordinates and time of your device, if it supports these functions. Otherwise you have to input the values manually, which also gives the possibility to select any place on Earth not too distant from the present. I'm hoping that I got the time zone selection right, since the date-time implementation of Javascript doesn't have that option. Be aware that with my implementation it is possible to set incompatible combinations of time zone and coordinates; don't expect a proper sky display if you do that. I'm still searching for a library that allows to set the time zone automatically with the coordinates.

Meanwhile, below is a regular interactive version of the asterism map, with zooming and panning.

Check out the documentation or download the D3-Celestial source in the GitHub repository.

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