We could say that modern astronomy began in 1609. That was the year when the telescope, invented by the Dutch in 1608, was first used to observe and describe celestial objects. Until telescopes were used, astronomy was primarily about measuring the positions of the Sun, Moon, and planets in the sky. This helped early astronomers make calendars and to plan their harvests, but people were unable to study the celestial bodies and learn their characteristics. A recently discovered lunar map indicates that Thomas Harriot of England was the first to observe and draw a magnified image of the Moon in July 1609.
Galileo Galilei, of course, is most well-known for building and using early telescopes. He did his lunar observations in December 1609 while observing from Padua, Italy. The prevailing idea at the time was that everything in the heavens had to be perfect and unblemished. Drawings of mountains, valleys, and craters on the Moon contradicted this idea, showing the Moon to be an ‘imperfect’ world like Earth. As Galileo published his drawings and Harriot did not, Galileo gets the credit for changing our concept of the universe, helping us realize that celestial bodies are worlds and not just sources of light.
On January 9, 1610, Galileo saw three ‘fixed stars’ next to Jupiter. Four days later he discovered a fourth and realized that these ‘stars’ orbited Jupiter. Today, those four moons– Io, Europa, Ganymede, and Callisto, are called the Galilean moons. The direct observation of moons orbiting Jupiter disproved Claudius Ptolemy‘s model of the universe, already centuries old at the time, which held that all bodies in the universe orbited the Earth.
In December 1610, Galileo observed Venus and saw that Venus showed phases like the Moon’s when magnified in his telescope. This meant that sometimes the sunlit side of Venus faces Earth, while at other times we see the night side, although Venus is never opposite the Sun in the sky. This could happen only if Venus orbits the Sun rather than Earth.
By the way, Galileo did far more than just astronomy. Rice University’s Galileo Project has more on his extraordinary life, including a timeline.
It was also in 1609 that Johannes Kepler published his New Astronomy, containing his first two laws. The first law states that each planet’s orbit is an ellipse rather than a perfect circle. The second law states that a planet sweeps out equal areas in equal times. Kepler published his third law, which relates the square of a planets period (time for one orbit) to the cube of its average distance, in 1619.
This makes 2009 the 400th year of modern astronomy. Appropriately, the United Nations declared this year to be the International Year of Astronomy. At that link, you can learn about events taking place all over the world promoted by the International Astronomical Union (IAU) and the United Nations Educational, Scientific, and Cultural Organization (UNESCO). Their goal is for people all over the world to discover the wonders of the sky and to appreciate our place in the universe.
You can participate in the International Year of Astronomy right here in Houston. Several of the Fun Hundred events we’ve set up to celebrate our 100th anniversary are astronomy-related. They include Sun-Earth Day at the vernal equinox, our annual viewing of the Perseid meteor shower in mid-August, members nights at the George Observatory, and a winter solstice event on our sundial.
Also, you can observe the phases of Venus in the first three months of this year, just as Galileo did through his telescope. Keep in mind that Galileo’s telescope looked like this; anyone with a good pair of binoculars has better observing equipment. Go outside at dusk and look west southwest for the brightest point of light in the sky. That is Venus. Through a telescope, you’ll notice that Venus appears half-lit in mid-January 2009. As you keep observing through March, you’ll see Venus become a more and more pronounced crescent. This is because Venus is coming around to our side of the Sun and thus turning more and more of its night side to Earth. The very skinny crescent of mid-March is so pronounced that it is noticeable in binoculars.
Remember, the great discoveries, or aha moments, as my co-blogger described, are not limited to great, historic scientists. The beauty of science is that anyone who takes the time to observe can share in the act of discovery.
