& a Guide to the Universe An Introduction to Astronomy

Before the invention of the telescope, observations and discoveries were made with the unaided, human eye. Early people viewed the sun, moon and stars as magical Gods, and worshiped them. This was an early attempt to explain the things such as rain, sickness, seasons and what held the Earth in the sky. Think Greek Myths!!!

One of the earliest uses for astronomy was explaining periods of time: days, seasons and years. World calendars have been set according to the sun and the seasons for a very long time.

Stonehenge, one of the earliest astronomical sites, was built in England. Its stones are closely aligned with the rising and setting points of the sun. People are beginning to notice patterns within the sky.

Aristotle argued that the Earth was an unmoving sphere in the center of other rotating spheres. He believed that the heavens, or outer space, were perfect and unchanging.

Eratosthenes of Cyrene was the first to accurately calculate the circumference of the Earth.

Greek astronomer, Ptolemy, published a manual describing his earth-centered model of the solar system in which the sun, moon, planets, and stars move in circular paths around Earth. This is called the Geocentric Theory.

During the Renaissance, Polish astronomer Nicholas Copernicus published his sun-centered model of the solar system. This is called the Heliocentric Theory. Out of fear, he did not publish it until he was near death. The theory stirred controversy because it went against religious beliefs of the period.

Geocentric Theory Vs. Heliocentric Theory

Danish astronomer, Tycho Brahe, noted that planetary orbits are oblong, not circular. Brahe observed a supernova, or exploding star, which challenged Aristotle’s idea that the heavens were perfect and unchanging.

GalileoGalileo was the first astronomer to use a telescope to study the sun, moon, planets, and stars. He discovered sunspots, craters and mountains on the moon, and the four largest moons of Jupiter. He also furthered the theory that the sun is in the center of the solar system.

Johannes Kepler created the three laws of planetary motion, which explained how the planets stay on one orbit around the sun and that once around this orbit is a year. He discovered that planetary orbits are elliptical rather than circular.

Sir Isaac Newton published Principia, in which he described his theories of gravity, motion, and the orbits of the planets. This explained how planets stay in their orbits around the sun and why people don’t fall off of planets.gravity

Thomas Wright stated that the Sun was just one of many stars in the Milky Way Galaxy, revolving around a common center of gravity.

Giovanni Schiaparelli discovers canals on Mars, leading scientists to believe there might be life on the planet. He also studies comets and their connection to meteor showers.

Albert Einstein published his general theory of relativity, explaining that matter curves space and affects how planets are attracted to stars. Advancing the work of Newton, he said that gravity could be explained with a mathematical formula using time and space.

Edwin Hubble created the modern model of the universe, which says that the Milky Way Galaxy is only one of many galaxies in an expanding universe.

A collection of stars and their planets held together by a common gravitational force.

No! Stephen Hawking’s recent work has proven the existence of black holes. We have sent probes into space that send new information back to Earth each day.

Expedition 35Expedition 35 is currently at the International Space Station.