Location, location!

Much of our viewing success is determined by our position on our planet and in the universe. Perspective plays a key part in what we observe.

The Sun and the Moon despite their contrasting sizes (diameter of Sun: 1,392,530 km compared to the humble Moon at 3,475 km). Both these bodies appear the same size as viewed by us- roughly 30 minutes of arc or ½ of one degree. This unique arrangement means that from time to time when these bodies line up correctly the tiny Moon is able to block out the gargantuan Sun and cause a total solar eclipse. Because the Earth is so much larger than the Moon its shadow cast on the Moon is much larger and Lunar eclipses are more frequent and last longer.

The planets: When the outer planets meet up with our orbit around the Sun they appear at their brightest as seen by us. This is called Opposition. Their size and distance from us determine how large their discs appear to be. Although Mars comes closer to us than the larger outer planets, its relatively smaller size and its more infrequent orbital meeting with us means that its image is small and only easily studied every two years.

Our Southern Sky:

Because the stars forming imaginary groups we call constellations are so far away from us they appear not to move relative to one another, although they all move though our Milky Way at different rates. All stars we observe are in our own Milky Way galaxy. However, our position on our globe, our daily movement around the Sun, and our 24 hour  earth rotation means that the skies we view keep moving and changing while parts of the northern skies and some constellations we never see from here. We are, however, fortunate that the best deep sky objects are visible from the Southern Hemisphere.

Our limitations:

Not only does our location limit what we see but clouds, a dense atmosphere, our visual limitations and light pollution hinder viewing. Humans have overcome this by building large telescopes and getting as high above Earth’s atmosphere as possible. Getting completely away from our atmosphere produces the wonderful sharp images though the Hubble Space Telescope. Despite all the above we are indeed fortunate to see so many beautiful sights in our night skies.

Amateur astronomers from Shoalhaven Australia.