It's been 400 years since Galileo Galilei pointed for the first time in history the newly invented telescope (a set of lenses) into the skies instead of using it for military purpose (for which it was invented for). He quickly discovered that the sky is much larger than expected and things up there do not match with current believes about how the world is functioning. The "knowledge" back then was highly influenced by the church(es) i.e. religions.

He first discovered that the moon is not flat but instead found craters and mountains to be plastic (3D) objects.

When pointing his telescope to the Jupiter the first time he figured three new stars close by the planet. The next night he was quite surprised that these "stars" had moved and also a fourth "star" appeared additionally. He concluded that these were no stars but instead moons orbiting around the Jupiter.

At the same time Johannes Kepler figured from the huge amount of observation data the most famous and advanced astronomer at that time, Tycho Brahe, left after his death, that the orbits of the planets are not a circle but instead an ellipse around the sun. He figured this for the planets Mars and assumed correctly that this is true for all other planets as well. He also provided the mathematics to calculate the positions of the planets correctly (3rd Kepler Law) but failed to explain why the planets orbit the sun the way they do.

This was done some 80 years later by Isaac Newton who took the findings of Galilei and Kepler and extended them by a complete new mathematic and his famous law of gravity.

The idea of the sun being circled by the planets (including the earth) was first developed by Nicolaus Copernicus 80 years before Galilei and Kepler approved it. Brahe didn't believed in Copernicus' idea but still placed the earth into the center of everything. Interestingly his observation data which provided the information for the elliptic orbits also provided the information for this theory.

To celebrate the 400th anniversary of the two most important events on which the modern astronomy, physics and understanding of the world is founded, this weekend (2.-5. April) a huge event is happening all around the world:

100 hours of Astronomy
http://www.100hoursofastronomy.org/

Around the world telescopes and planetariums are opened to the public to give everyone the chance to get first hand pictures of what going on above us. To see stars, nebulae's and galaxies with the own eyes.

A special event is

Around the world in 80 Telescopes
http://www.100hoursofastronomy.org/webcast

where 80 telescopes around the world provide a 24 hours continuous webcast. The webcast starts on Hawaii and will end there 24 hours later again.

Currently the servers seem to be down due to the high load but I strongly recommend to take a look on them later today/tonight.