*Section 1* Astronomy: The Original Science
- Astronomy: Study of the universe
- Year: Time required for the Earth to orbit once around the sun
- Month: Roughly the amount of time required for he moon to orbit once around the Earth (from moon)
- Day: Time required for the Earth to rotate once on its axis
In 1543, Corpenicus (Polish astronomer) came up with a new theory that revolutionize astronomy.
- Telescope: an instrument that gathers electromagnetic radiation from objects in space and concentrates it for better observation.
- Refracting telescope: a telescope that uses a set of lenses to gather and focus light from distant objects
- Reflecting telescope: a telescope that uses a curved mirror to gather and focus from distant objects
- Electromagnetic Spectrum: all of the frequencies of wavelengths of electromagnetic radiation
- Constellations: a region of the sky that contains a recognizable star pattern and that is used to describe the location of objects in space
- Zenith: the point in the sky directly above an observer on Earth
- Altitude: the angle between an object in the sky and the horizon
- Horizon: the line where the sky and the Earth appear to meet
- Light-year: the distance that light travels one year; about 9.46 trillion kilometers
Early astronomers helped people understand their place in the universe
They only had their senses to believe in and the oral theories from the other astronomers
As expected, most of the early astronomers thought that the universe consisted of the sun, the moon, and the planets.
They thought that stars were at the edge of the universe
Claudius Ptolemy and Nicolaus Copernicus were the early scientists who helped define the structure of the universe
Ptolemy's theory was that the Earth was the center of the Earth
This theory was indeed wrong, but was the best and the most persuasive theory back then
This theory was famous for 1,500 years all over Europe
His theory said that the sun is at the center of the universe and all of the other planets orbited the sun.
This theory was the truth but wasn't persuasive and strong enough to replace the Ptolemaic theory for quite a time.
When this theory was finally accepted, the "Copernican revolution" took place.
In the late 1500s Tycho Brahe (Danish astronomer) used several large tools and made the most astronomical observations that had been recorded so far.
Brahe believed in the theory that said the sun and the moon revolved around the Earth and that the other planets revolved around the sun
Even though this theory was not correct, Brahe recorded very precise observations of the planets and starts that helped future astronomers.
Johannes Kepler (Brahe's assistant) continued Brahe's work when Brahe died
He did not agree with Brahe's theory but found his data quite useful.
In 1609 Kepler announced that all of the planets revolve around the sun in elliptical orbits and that the sun is not in the exact center of the orbits.
He also stated three laws of planetary motion, which are still used today
In 1609, Galileo Galilei became one of the first people to use a telescope to observe objects in space.
He soon discovered the craters and mountains on the Earth's moon, four of Jupiter's moons, sunspots on the sun, and the phases of Venus
This discovery proved to the people that the planets are not "wandering stars", but are physical bodies, just like Earth.
In 1687, Sir Isaac Newton showed that all the objects in the universe attract each other through gravitational force
The law explained why all of the planets orbit the most massive object in the solar system (the sun).
Newton helped explain the observations of the scientists who cane before him, ultimately.
Before the 1920s, many astronomers thought that our galaxy, the Milky Way, included every object in space.
In 1924, Edwin Hubble proved that other galaxies existed beyond the edge of the Milky Way.
This led to the conclusion that the universe ids much more bigger than our galaxy
*Section 2* Telescopes
Optical telescopes are the most common type of telescope that are usually used to study visible light from objects in the universe.
Without an optical telescope, you can see at about 3,000 stars in the night sky.
However, when you use a optical telescope, you can see millions of stars and other objects that were not visible to naked eyes.
A focal point is the point where the rays of light that pass through a lens or that reflect from a mirror converge.
Objective lens (one lens) collects light and forms an image at the back of the telescope.
The bigger the objective lens is, the more light the telescope can gather.
The largest reflecting telescopes are the Keck Telescopes in Hawaii which are twin telescopes that each have 36 hexagonal mirrors that work together.
Linking several mirrors allows more light to be collected and focused in one spot.
The light gathered by telescopes on the Earth is affected by the atmosphere.
The Earth's atmosphere causes starlight to shimmer and blur due to the motion of the air above the telescope.
Electromagnetic spectrum consists thermal light, radio waves, infrared light, ultraviolet light, X rays, and gamma rays.
Nonoptical Telescopes detect radiation that cannot be seen by the human eye.
Astronomers study the entire electromagnetic spectrum because each type of radiation reveals different clues about an object.
*Section 3* Mapping the Stars
When people in ancient cultures connected stars in patterns, they named sections of the sky based on the patterns.
Constellations help organize the sky and make the astronomers easier to find their way.
