Friday, 13 November 2015

Venus, Mars, Jupiter Conjuntion, Photographed with an iPad

In recent weeks there have been some nice conjunctions of the planets and the moon in the eastern sky, early in the morning.  I took some photos, shown below, mostly with the iPad.

For the sake of context, the first image is that given on the CBC news Science website, of October 27, 2015.  That shows the alignment that was expected.

The next photo was taken with my iPad, early in the morning of October 28, 2015.  It has been enlarged and enhanced, using the Gimp image processing program (turning up brightness and contrast).  As you can see, Venus (magnitude -3.5)  and Jupiter (magnitude -0.9) were captured quite well by the iPad, but Mars (magnitude 2.4) is just barely visible.

The magnitude scale is a funny beast.  Smaller numbers indicate brighter objects (e.g. a magnitude 1 star is much brighter than a magnitude 2 star).  For a few objects, the magnitude scale actually has to go into the negative numbers, to make sense.  So, Venus at -3.5 is much brighter than Jupiter at -0.9).  This interesting scale goes back to ancient times.  Essentially, a difference of 5 magnitudes is equivalent to a difference of 100 times in absolute brightness.  This odd scale actually does a pretty good job at reflecting how the human eye sees differences in brightness (a logarithmic or power law response, rather than linear), so it has been kept by modern astronomers.

The third picture is the same scene, taken at about the same time, but with a regular digital camera (a Canon PowerShot A1000IS). It seems to register about the same as the iPad, perhaps a bit better.  However, the differences are slight, at best.

The last picture shows the same scene, about a week later.  The moon has now joined the planets in the eastern sky.  It is actually a crescent moon – the light has spilled into some of the other CCDs on the iPad, “fattening” it up.  This was then reinforced by the brightening in the image processing software, needed to bring out the planets more strongly.

Jupiter is now quite a bit farther away from Venus, in this image.  Also, Mars can’t be made out.  Either the seeing wasn’t quite as good, or the presence of the moon has washed out the nearby sky too much to allow the iPad to capture Mars.


Incidentally, you can use the distance (in degrees) from the sun to venus, as seen from the Earth, and the alignment of the planets during the conjunction to estimate the distance from the Earth to each planet.  It can be done both graphically and via some high school geometry (law of sines and law of cosines).  It is an interesting excersise for a later blog :).


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Kati of Terra Book 1: Escape from the Drowned Planet

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The Witches' Stones Book 1: Rescue from the Planet of the Amartos

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