Midterm Study Guide for Astronomy 101

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Cosmos – an alternative name for the universe
Meridian – a half circle extending from your horizon (altitude 0) due south through your zenith to your horizon due north. Zenith – the point directly overhead, which has an altitude of 90 degrees. Latitude –The angular north-south distance between Earth’s equator and a location on Earth’s surface. Longitude – The angular east-west distance between the prime meridian (which passes through Greenwich) and a location on Earth’s surface. Speed – The rate at which an object moves. Its units are distance divided by time, such as m/s or km/hr. Velocity – The combination of speed and direction of motion; it can be stated as a speed in a particular direction, such as 100 km/hr due north. Force – Anything that can cause a change in momentum.

Momentum – The product of an object’s mass and velocity. Acceleration – The rate at which an object’s velocity changes. Its standard units are m/s squared. Kinetic energy - Energy in motion, given by the formula (1/2)m * v squared. Gravitational potential energy - Energy that an object has by virtue of its position in a gravitational field; an object has more gravitational potential energy when it has a greater distance that it can potentially fall. Power – The rate of energy usage, usually measured in watts (1 watt = 1 joule/s). Wavelength - The distance between adjacent peaks (or troughs) of a wave. Frequency – The rate at which peaks of a wace pass by a point, measured in units of 1/s often called cycles per second or hertz. Redshift – (Doppler) A Doppler shift in which spectral features are shirted to longer wavelengths, observed when an object is moving away from the observer. Focal plane – The place where an image created by a lens or mirror is in focus. Light pollution – Human made light that hinders astronomical observations. Terrestrial planet - Rocky planets similar in overall composition to Earth. Jovian planet – Giant gaseous planets similar in overall composition to Jupiter. Kuiper Belt – The comet- rich region of our solar system that spans distances of about 30-100 AU from the Sun. Kuiper belt comets have orbits that lie fairly close to the plane of planetary orbits and travel around the sun in the same direction as the planets. Oort Cloud – A huge, spherical region centered on the Sun, extending perhaps halfway to the nearest stars, in which trilliuons of comets orbit the Sun with random inclinations, orbital directions, and eccentricities. Orbital energy – The sum of an orbiting object’s kinetic and gravitational potential energies. Spectrograph – An instrument used to record spectra.

Photons – An individual particle of light, characterized by a wavelength and a frequency . Ptolemy is credited with being the person who computed the most authoritative tables for calculating the past present and future position of the planets. His tables were the most authoritative throughout the middle ages . Ptolomy's view of the universe was an earth centred universe with the planets orbiting in spheres but also spheres within spheres which made his model more useful than the preceding models . Galileo gave credence to Copernicus's claims that the Sun was the center of the universe, not the Earth. He also perfected the USE of the telescope, he DID NOT invent it. With his telescope, he observed sun spots, proved that the Moon had mountains and craters, discovered the four moons of Jupiter, and that Venus goes through phases. Copernicus was an astronomer who stated that the sun was at the center of our solar system and that the planets rotated around it. Up until that time it was commonly believed that the planets, and the sun, rotated around the Earth. He wasn't the first, but was definitely the most famous for it. He also worked to develop better telescopes during the course of his studies. Brahe 1) Observing and measuring the (rough) distance to a supernova, establishing novae as outside the solar system. This proved...
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