Aristotle believed in a geocentric universe (the Earth is the center of the universe) and that the stars and planets were perfect spheres except the Earth. Today we know none of this is right.
Ptolemy believed in a geocentric universe and developed Ptolemy's Cosmology. The planets/star went in the order: Earth, Moon, Mercury, Venus, Sun, Mars, Jupiter, and Saturn. In his time only five planets were known to exist.
Copernicus developed the theory of a heliocentric universe (the sun is the center of the universe). All of his observations were done with a naked eye. He thought that every planet including the Earth revolved around the sun.
Tycho Brahe made consistent observations that supported Copernicus's theory of a heliocentric universe. He also listed 1000 stars and found differences in the Moon's orbit
In 1609 Galileo built a telescope and in the following year published his findings. He described the "highland and the seas" of the moon, Jupiter's four largest moons, and new stars. He also confirmed Copernicus's theory of a heliocentric universe by finding Venus's phases of sunspots.
Hans Lippershey was a Dutch eyeglass maker who is believed to have invented the telescope. One story involving the invention is, Lippershey saw two kids playing with two lenses. The kids found that when they looked through the lenses they could see things that were far away more clearly. Lippershey then put a tube between the lenses making a telescope.
In 1600 after Kepler published his work, The Cosmosgraphic Mystery, Tycho Brahe invited Kepler to Prague to become his assistant in calculating new orbits for the planets. Kepler heard of Galileo's findings and when he got a suitable telescope he published, Jupiter's satellites, which was enormous support for Galileo.
Cassini observed Jupiter's Red Spot and was one of the first to see Mars's Polar Caps. He also observed Venus's phases and found Jupiter's oblateness. He also discovered four of Saturn's moons and found that the rings were separated by gaps and found that the rings were made of small particles.
Sir Isaac Newton
Newton became a leader in science when he finished his work on universal gravitation, diffraction of light, centrifugal force, centripetal force, inverse-square law, bodies in motion, and the variations in tides due to gravity.
In 1781 Herschel discovered Uranus while trying to determine stellar parallax. In 1782 he discovered two moons of Uranus and two more moons of Saturn. Herschel also worked on double stars which provided the first demonstration that gravity was also outside our solar system.
While looking for a ninth planet Lowell found Pluto. Lowell discovered canals on Mars, but studies by other astronomers found that there were no canals. Lowell was determined to see a landscape on Mars so he made an observatory in Flagstaff so he could look for the canals.
Hertzsprung was the first to was the first to calibrate the period-luminosity relation for Cepheid variable stars. He determined proper motions, colors, and magnitudes for many stars in the Pleiades cluster. He also measured about a million photographic positions of binary stars.
When Einstein published in his general theory of relativity in 1916, he was able to account for the variations in the orbital motions of the planets. He won a Nobel Prize for Physics in 1921 for photoelectric effect. It explains that light contains particles called protons. He also stated that light was a constant in his special theory of relativity.
Hubble discovered that the Milky Way galaxy was just one of many galaxies in the universe. He collected enough data from different galaxies to invent a way to classify them. He also found that the further away a galaxy was from another, the faster they would move away from each other.
Jansky was assigned the task of finding the sources of static that might interfere with radio transmissions. He ended up finding three different kids of static: nearby thunderstorms, farther away thunderstorms, and an unknown third. After over a year of investigation he found out that it was radiation coming from the Milky Way.
On October 4, 1957, the Soviet Union launched Sputnik I. It was the world's first artificial satellite. It took 98 minutes to orbit the Earth on its elliptical route. It marked the start of the Space Race with the Soviet Union and the US.
On April 12, 1961 Gagarin became the first person to orbit the Earth in his spacecraft, Vostok I. The spacecraft orbited the Earth at a speed of 27,400 kilometers per hour. The flight lasted 108 minutes and at the highest point, he was 327 kilometers above Earth.
On February 20, 1962, Glenn became the first American to orbit Earth. He orbited the Earth three times in his spacecraft, Friendship 7, at speeds more than 17,000 miles per hour. It flight took four hours and fifty-six minutes.
The Apollo Program
The Apollo Program was made to take humans to the Moon and bring them back safely. Six of the Apollo missions did have people land on the moon and return safely. On the six missions 400 kilograms of lunar samples were collected and experiments were conducted.
On July 16, 1969, Armstrong became the first person to ever walk on the moon. He was aboard Apollo 11 with Buzz Aldrin and Micheal Collins. At 10:56 pm Armstrong takes his first step on the moon. On July 24, they land safely back on Earth.
First Space Shuttle Flight
On April 12, 1981, the Space Shuttle Columbia launched into orbit with John Young and Bob Crippen. It was the first reusable spacecraft that could be recovered in the ocean. The only things that could not be recovered was the external fuel tank, which would burn up upon coming back to Earth.
Mars Pathfinder Expedition
On December 4, 1996, the Mars Pathfinder was launched. It landed on Mars on July 4, 1997. I was the first robotic rover to be launched on Mars.
On October 15, 1997, the Cassini orbiter begins a 7-year long journey to Saturn. On June 30, 2004, after a 2.2 billion mile journey, it finally reached the Saturn System. One of the Cassini's biggest achievements was making the first landing on a moon in the outer solar system.
Refracting and Reflecting Telescopes
Telescopes are instruments that are used to gather light from distant objects. Refracting telescopes use convex lenses, at the front of the instrument to get and focus the light. The image is then magnified through an eyepiece lense. Reflecting telescopes use a "primary concave" mirror to gather the light. A different mirror is then used to bring the light rays to a detector.
Hubble Finds a New Galaxy
When astronomers used the Hubble Space Telescope to take a picture of the globular star cluster NGC 6752 they accidentally captured an image of a new dwarf galaxy. The galaxy is barely one thirtyth the Milky Way Galaxy. The galaxy is thirteen billion years old and is considered a living fossil from the early universe.