Saturday, June 11, 2016



What does the word "Humongous" mean?  It means large, it means enormous.

When we look at the night sky we see stars.  If it is a very dark night and we are far away from light pollution then we can see the 'Milky-Way' (our home galaxy) and we can see 'more-stars'.

When the full moon is high in the night sky it appears to be a small disk.  

The amount of sky any astronomical object uses up is measured in arc-degrees and arc-seconds. The entire sky or celestial sphere is 360 arc-degrees in circumference when you consider the entire sky from pole to pole and all the way around the planet.  

This means at night from any one spot on the planet at any particular instant you can only see one half of the sky (the other half is on the other side of the planet, called the 'daylight-sky').  The planet rotates so during the night more than 1/2 of the entire sky will be visible during the night as stars set and stars rise. 

So, back to the full moon.  The full moon uses up a square of sky equal to 31 arc-minutes or about 1/2 a degree on a side.  The sun takes about the same amount of space in the sky which is why, during a total solar eclipse, the moon can 'blot-out' the sun.

Using telescopes we can magnify the part of the sky we point the telescope toward and see distant objects appear bigger.

Since the invention of time-lapse photography things have become much more interesting.  For daylight photography we can watch a flower bloom, or we can watch clouds develop and sweep over the landscape.  There are lots of very cool videos of the night sky using time lapse photography.

There is another extremely cool us of time-lapse-photography and that is the ability to keep a telescope pointed at the same place in the sky and keep it moving to correct for the rotation of the earth so that patch of sky is always centered in the view.  Then instead of taking a video all the light collected from the telescope is collected on a single frame.  The result is that dim objects in the night sky can be made visible.  The Hubble Space Telescope works this way and we see wonderful pictures.  

When magnification is not used much we can now use telescopes to see dim objects in the sky and that are not magnified very much to just collect all the light from some patch of sky and see what shows up.

The Astronomy Picture of the Day for today 11 June 2016 looks at a patch of sky that would hold a 4x4 grid each grid element being the size of the full moon.  The galaxies in the picture are over 20 times further away than the Andromeda galaxy, the closest galaxy to the milky-way.  If the same patch of sky had the Andromeda galaxy in it would fill almost all the patch.

When you look at the night sky think of the full moon and how much space it would be taken up if you arranged 16 full moons in a 4x4 square.  Then think what you would see if you collect all the light from that patch of sky to reveal the very dim objects in the patch.

The picture you would get is today's APOD: