To make sense of which parts of the universe is visible, I have tried to construct some simple concepts of our place in the universe. 

The view from earth at midnight, is much like light from  a lighthouse. The view, shown as a "tube", is tilted from the plane of the Milky Way, following earths orbit around the sun. In June the view is of the core of the Milky Way. The core blocks the view of the  universe beyond the core. 

Understanding the view from earth is a bit of a brain-tease that has confused people on and off for thousands of years. For the purposes of viewing the Universe, we need the darkest possible skies. 

Days - Earth spins on its axis, giving rise to our days and nights.


Months - determined by the orbit of the moon around the earth that gives rise to our monthly cycle and the daily tides. The best viewing are found with the darkest skies that occur when at midnight, the moon is on the same side as the sun. The moon appears during the day and is backlite by the sun - a "New Moon".  

Earth orbits the sun, giving rise to our year. The Earths spin axis points  at the star Polaris and is  tilted 23 degrees to the plane earth/sun orbit, giving rise to the seasons. In June with summer in the northern hemisphere occurring when  oriented  with the spin axis. For the observer, the nights in the northern hemisphere are longest. 

The darkest sky occurs at midnight when the observer is on the opposite side of earth to the sun. The simplest reference view is 180 degrees centered on directly overhead. In the spin direction, the view from dark skies after sunset to sunset covers a roughly 270 degree view. 

The white hemispheres illustrate the view from the equator relative to the ecliptic. The plane of the earths spin rotation, affects the view in June and December.






The sketch shows the how the view of the Milky Way works. It starts from the Suns location in the plane of the Milky Way. 

The earth-sun orbital plane (ecliptic)  is oriented at 63 degrees to the plane of the Milky Way pointing at the galactic center.  The north spin axis of the Earth at 23 degrees to the ecliptic, is oriented away from the center of the Milky Way, fixing the seasons so that earth is positioned between the core and sun in June.  The overhead view from the equator  on earth at midnight is always directly away from the Sun. At midnight  in June, the view  is of the center of the Milky Way.  At midnight in December, the overhead view from earth is directly way from the center of the Milky Way. 

The "pictures" of the Milky Way are for an observer at the equator. As the observer moves towards the poles, portions of the core get obscured. 

Andromeda and other deep sky objects outside Milky Way are visible in mid-winter.



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