Astronomy Unit 3
-circle can be divided into 360 degrees, each degree into 60 minutes of arc, and each minute into
60 seconds of arc
-the symbols (°, ', '') are used
-Galileo Galilei-made basic investigations into physical motions and was among the first to use a
telescope for astronomical observations
-Heliocentric theory- the earth orbits the Sun
-Linear measure is the straight-line distance between two points
-Measured in meters or kilometers
-Angular measure is a measure of the difference in direction between two points as seen from a
specified third point
-Measured in degrees, minutes, and seconds
-The order of the planets
-My Very Energetic Mother Just Served Us Noodles
Planet as defined by the IAU
-The orbit must be circular enough not to cross the orbit of another planet.
- A planet must also have enough mass to become nearly spherical.
- And a planet must be able to sweep other small astronomical objects out of its orbital
-Opposition when a planet is nearer to the Earth than to the Sun
-Conjunction- when a planet is nearer the Sun than Earth
-Astronomical Unit (AU) is the average distance of the Earth from the Sun:
-1 AU = 1.5 × 10 ^11 meters
-Synodic Period- Ex: the time between full moons
-Sidereal period- interval with respect to the stars.
Perihelion- When the planet is closest to the Sun
-When the planet is most distant from the Sun.
Kepler’s three laws:
1. Orbits are ellipses with Sun at one focus. The shape of a planet’s orbit.
2. Line joining planet and Sun sweeps out equal areas in equal times. How a planet moves in its
orbit. 3. Squares of sidereal periods are proportional to cubes of semi-major axis The relation of the
average speed to the size of the orbit.
Astronomy Unit 4
-radio telescopes are reflectors
-focal length of a lens or mirror is where the image of a distant object falls