Top 10 moments in Astronomy

Top 10 Moments in Astronomy

Astronomy has come a long way since humans peering at the night sky began asking, "what the heck is going on up there?"
Zoom through the 10 favorite galactic conundrums that keep scientists guessing.

10. Copernicus Puts Earth in Its Place

Through most of our history, humankind hardly understood anything about the universe -- yet always thought we were at the center of it. That is, however, until Nicolaus Copernicus came along in the 16th century. Astronomy was in a pretty sorry state as calendars were embarrassingly out of sync with the seasons. To explain this and other discrepancies, Copernicus set out to prove Aristotle's theory that the Earth was in motion, with the sun at the center of the picture.

His new hypothesis inspired the first accurate diagrams of the solar system and -- although the Catholic Church wasn't too fond of it -- this big idea paved the way for future groundbreaking astronomical discoveries.

9. Kepler Calculates Cosmic Mechanics

Johannes Kepler, now heralded as the father of celestial mechanics, believed that the language of God was geometry. No surprise, then, that the 16th century astronomer set out to understand stars movement through a devout application of mathematics. With a little help, Kepler eventually proved that the planets' orbits were elliptical -- not perfect circles as astronomers once believed them to be.

Kepler also figured out that the speed of anything orbiting the sun changes predictably according to distance from the sun (the closer, the faster). We now call his findings Kepler's Laws and, when it came to planet-sun distance, the tables Kepler created were 10 times more accurate than those of Copernicus.

8. Newton Drops Some Gravity

In spite of Kepler's breakthroughs, he still didn't know what caused all of the motion in the cosmic merry-go-round. So in 1666, Sir Isaac Newton stepped into the picture by breaking new astronomical ground: He applied three new laws of motion and formulated a law of universal gravitation, aka gravity.

This new law dictated that every piece of matter attracts every other piece, with the force hinging on the mass and distance. Newton used the new work to suggest that the sun's far-reaching gravity held the Earth and other planets in their orbits, and that gravity was one of the key forces in the universe.

7. Galileo Spies Jupiter's Moons

Not everyone was on board with the whole "Earth revolves around the sun" thing, however. Some critics pushed for a compromise in which our planet orbited the sun -- but everything else in the universe revolved around our home planet. Even after the devout bowed to the scientific facts, they felt comforted by the fact that the moon revolved around the Earth... and no other planet had any of those.

Wrong again. None other than Galileo Galilei burst their bubble in 1610 by watching a series of "stars" near Jupiter, later shown to be moons.

6. Herschel Maps the Heavens

Astronomy ain't easy. Just mapping the solar system took the better part of four centuries. Even Pluto didn't make the planetary roster until 1930, and was demoted to a dwarf planet in 2006. If charting the solar system took so long, then the prospect of mapping the starry sky really is as daunting as it sounds.

William Herschel, however, wasn't deterred. With help from his sister Caroline, the British astronomer charted more than 800 double stars and 2,500 nebulae in the Milky Way before his death in 1822. Bonus: He discovered the planet Uranus in the process. His final model -- based on telescopic observation of 2,400 areas in the night sky -- featured more than 90,000 stars and revealed that the Milky Way is a disc-shaped galaxy.

5. Einstein Gets Relative

By the late 19th century, scientists began to feel the limits of Newton's laws. Quite simply, they fell short in explaining certain galactic phenomena, including how Mercury accelerated faster than expected at its closest approach to the sun. This is where Albert Einstein stepped in with the idea that time and length were relative to the observer, introducing all sorts of gedanken experiments that confuse us to this day.

Einstein's theory of general relativity, developed between 1915 and 1919, proposed that mass warps both space and time -- which permits large masses such as stars and galaxies to noticeably bend light.

4. Hubble Contemplates an Expanding Universe

The Milky Way galaxy used to be the universe at large; the idea that our host galaxy was just one of billions of collections of stars was unheard of.

Edwin Hubble arrived on the scene in the 1920s, making a name for himself by discovering several distant nebulae were instead other galaxies. As if this monumental discovery weren't enough, Hubble went on to make another galactic breakthrough: The universe is constantly expanding. His calculations on galactic distances drummed up major support for the Big Bang theory of how the universe came to be.

3. Jansky Turns on the Galactic Radio

Ever tried to tune into a football game on the radio, only to fight the static to figure out who just scored a touchdown? Congratulations -- you've encountered radio interference (some of it from outer space).

Karl G. Jansky, an engineer at Bell Telephone Laboratories, encountered similar interference while fine-tuning the new trans-Atlantic radio-telephone service in the late 1920s. Only the interfering signal wasn't coming from the local station -- it was coming from the center of the Milky Way galaxy. In the years to follow, other radio engineers and scientists followed up on Jansky's find, eventually leading to the discovery that stars and other cosmic bodies emit radio waves. A distant star dim in the way of observable light could have a rather strong radio signal -- which made a great case for radio astronomy.

2. Extrasolar Planets Confirmed

As astronomers beefed up their tool kits, they seriously began to ask: Are there other planets beyond the solar system?

In October 1995, Swiss astronomers Didier Queloz and Michel Mayor made the first definitive sighting of a true extrasolar planet, called 51 Pegasi b. The planet is too far from Earth to view directly, but Queloz and Mayor cleverly detected it by seeing the light of its parent star dim as the planet eclipsed it from our Earthly observing platform. Today the number of extrasolar planets pushes 350, thanks to new techniques such as measuring how exoplanets gravitationally tug on their home stars.

1. Cosmic Creation Leftovers Discovered

Like forensic investigators looking for pieces of a bomb after an explosion, astronomers sought signs of the biggest blast imaginable: The Big Bang.

In 1964, the radio wave-based search of Robert Wilson and Arno Penzias paid off by mapping out a cosmic quilt of radiation left behind by the creation of the universe. Called the Cosmic Microwave Background, or CMB, the "afterglow" of microwave radiation is thought to have been made when the cosmos was full of searing hydrogen plasma. We can still see it today thanks to the relative nature of the universe.

For their discovery (about 20 years in the making) Wilson and Penzias jointly scooped up a 1978 Nobel Prize in physics -- and forever changed the way we think about the universe.