Thursday, 13 April 2017

Big Dipper with iPhone 7 – March 2017

Big Dipper with iPhone 7 – March 2017

I recently got an iPhone 7, and decided to test it with the Big Dipper, early one morning.  Here’s the result, with a little enhancement in GIMP.

The lower picture uses the GIMP brightness threshold filter, to only show pixels of a certain brightness.  This effectively isolates the stars of the Big Dipper.

2017 iPhone 7 photo.  

Here’s an inverted picture of the second image.


You can see how the iPhone picked up pretty well all of the stars of the Big Dipper, and even split the optical double, Mizar and Alcor (the second last star of the handle).  Bear in mind that the Big Dipper was somewhat close to the horizon (note the trees in photo number 1), so there would have been some extinction of the light through the atmosphere.

Note that the stars are somewhat blurred, though not by very much.  Since the iPhone 7 was hand-held, there was naturally some blurring.

Below is a photo that was “pushed” even further in GIMP.  I have labelled the stars by their names and magnitudes (lower magnitudes are brighter).  I also include a picture of the Big Dipper I took in fall 2015, with an iPad.  I also labelled the main stars on that one.  As you can see (I hope), the iPhone 7 photo is much sharper than the iPad photo, so the CCDs in the iPhone must be more sensitive in that camera.

When you take the picture, your first reaction will probably be that there isn’t much there.  It helps to take the picture when the seeing is exceptionally good, if course. The autumn months are often the best time of year for this, as the atmosphere is relatively dry and clear (vegetation is not very biologically active, so the air is dry), but the iPhone camera took a nice photo, even in the spring.
After taking the picture, you have to push the image in an imaging processing program, like GIMP or even iPad's own photo editing app.  Turn the brightness way up, the raise the contrast slowly as well.  The stars will come out, like magic, though you will want to experiment with settings, to get the best effect.  Some of the other features of GIMP (like the threshold filter, or the sparkle filter) can also help bring things out, or eliminate background clutter.
I will use wiki, to give a brief overview of The Big Dipper:

  • It is an asterism, not a constellation.  That’s a collection of stars that resemble some easy to see shape, whereas a constellation is a region of the sky. 
  • It has been interpreted in many ways by different cultures – for example, a dipper, a plough, a cleaver, a canoe, a wagon, and a coffin.
  • It is part of the larger constellation, Ursa Major, of the Great Bear. 
  • This is a circumpolar constellation, which means that it is visible year round in the Northern Hemisphere.
  • The end of the bowl stars point to Polaris, the North Star.  That star, of course, always is found in the northern sky, nearly due north.
  • The stars of the Big Dipper are all relatively close to the Earth, at 50 to 125 light years.
  • Most, but not all, of the stars of the Big Dipper are moving as a unit through the sky.  In 50,000 years, the shape will have changed, though it will still be dipper like (but reversed).
  • The optical double, Mizar and Alcor have long been used as a test of sight.  There is a tradition that the Roman army tested the eyesight of its soldiers that way.
  • The Big Dipper is easy to find and is used to locate other constellations – e.g. “arc to Arcturus”.
  • Another easy constellation is Cassiopeia, which is directly across the sky, with Polaris roughly in the center, between the Big Dipper and Cass.
  • There are some nice deep sky objects near the dipper, including the bright galaxies M81 and M82.

Now that you have read some real science (astronomy and astrophysics), you should read some science fiction.

Kati of Terra

How about trying Kati of Terra, the 3-novel story of a feisty young Earth woman, making her way in that big, bad, beautiful universe out there.

The Witches’ Stones

Or, you might prefer, the trilogy of the Witches’ Stones (they’re psychic aliens, not actual witches), which follows the interactions of a future Earth confederation, an opposing galactic power, and the Witches of Kordea.  It features Sarah Mackenzie, another feisty young Earth woman (they’re the most interesting type – the novelist who wrote the books is pretty feisty, too).

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