2021-08-15

Modern Wonders 4: Night Sky in a Box

tags: wonders

Yesterday evening the neighbours invited me over. We had a little camp fire, plus some roasted goodies including (but not limited to) marshmellows. I didn't see such things for a long time :-) And we watched the sky for some time. The moon was soon to set, but the sky only became dark enough to see the Perseid meteors until after midnight.

What impressed me though, was a piece of software to run on one of the available smart phones. It featured a point and annotate the night sky sort of augmentation of reality.

In order for this to work a number of other wonders are involved in this game:

a box the size of a hand hosting fairly impressive computing power

including a brilliant screen

a GPS/Glonass/Galileo receiving chip, receiving radio signals well below the electromagnetic noise floor, and deriving impressively accurate time and position on the planet from these radio signals.

a 3-axis-sensor for acceleration to find out the direction of gravity and thus vertically up and down, and the phones tip and tilt angles from that

a 3-axis-sensor for the Earths magnetic field, aka. compass to derive azimut

a large database of astronomical data, positions, orbital elements and what not

a non-trivial piece of software to create a fairly responsive map of what was to see above (or below for that matter)

the phones camera could have been used as well to calibrate directions, however, I'm unsure whether this was the case yesterday

Before the handheld data center times this took at least a map of the sky on paper and endless tables of numbers known as The Astronomical Almanac [a] and some serious numbercrunching using pen, paper, a slide rule or some other method of calculation.

XEphem [b,c] seemed like a giant step forward, and it was at the time. I even paid some money to have the full astronomical catalogs available at the time (ca. 1990).

While Apps on handhelds are all the rage these days --- am I alone to think that a "Night Sky in a Box" is a pretty impressive feat?

Cheers,

~ew

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[a] wikipedia Astronomical Almanac

[b] wikipedia XEphem

[c] github XEphem

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