Astronomy 101 Exam 1

Eclipse

When an object casts a shadow on another object

Lunar Eclipse

When the Earth is in between the Moon and the Sun, it casts a shadow on the Moon

Celestial Sphere

Designed by the Greeks to study the sky; a sphere that contains all the stars we see on the sky and rotates around the Earth every 24 hours

Circumpolar stars

stars that never rise or set; the closer you are to the poles, the more this occurs

Zenith

the point directly above your head if you look up at the sky

Altitude

Angle that the star makes with the horizon.

Reason for the seasons

Earth’s tilt

Luminosity

Amount of energy an object emits per time

Astronomical Unit (AU)

Average distance between the Earth and the Sun. The Earth is 1 away from the Sun. One is about 150 million km (93 million miles).

Light-year

Measurement for distance. It is the amount of distance light can travel in a year.

Parsecs (pc)

For bigger distances we use this measurement, which is 3.26 light years.

Gigayears (Gyr)

measurement for years in billions

Perihelion

The point on Earth’s orbit that it is closest to the Sun (this occurs during January)

Aphelion

The point on Earth’s orbit that it is furthest from the Sun (this occurs during July)

Geocentric model

Model where the Universe rotates around the Earth

Ptolemy (Claudis ptolemaeus)

Founded the geocentric system

Tycho Brahe

Built an observatory to measure precision location of objects in the sky. He invented the geo-heliocentric model where the Earth was still in the center while the planets orbited around the Sun.

Nicolaus Copernicus

Created the heliocentric system

Copernican model or the heliocentric model

The Sun is in the center of the model and all the planets orbit around it.

Johannes Kepler

 Wrote 3 laws of planetary motion; Worked for Tycho Brahe and tried to make his theory work

Kepler’s Three laws of planetary motion

1. All planets around the Sun move in ellipses.

2. A planet sweeps the same area of the orbit in the same interval of time.

3. The longer it takes a planet to complete its orbit, the further away it is from the sun

   • Specifically, P^2=a^3

Galileo Galilei

• Aimed a telescope to the sky (did not invent the telescope)

• Found that Jupiter had several moons orbiting it (the Galilean Moons)

• Discovered the Sun’s rotate

• Identified mountains on the Moon

Red photons

carry less energy

Blue photons

carry more energy

William Herschel

Not all light is visible; discovered infrared light; discovered Uranus and 4 moons using telescopes he developed