Astronomy Test #I Study Guide

Astronomy 7N Test #1 Study Guide GRAVITY Newton's Laws ↳ First law: an object at rest, or in motion in a straight line at a constant speed, will remain in that state unless acted upon by a force ↳ Inertia ↳ EX: If the Sun suddenly disappeared, the Earth would continue in the direction that it was traveling in its orbit at that time   [Diagram of a circle labeled "Sun" with an arrow showing the Earth's orbit] ↳ Second law: the acceleration of a body due to a force will be in the same direction as the force, with a magnitude inversely proportional to its mass ↳ Force = mass x acceleration (F=ma OR a=F/m) ↳ A smaller mass will move faster, if the same force is applied to it ↳ Third law: for every action there is an equal & opposite reaction ↳ EX: the Sun exerts force on planets & they orbit it -> the planets exert equal force on the sun, but it only moves slightly because of its very large mass relative to the planets ↳ EX: a person standing still on Earth gets pulled down but is also pulling the Earth up towards them   Surface Gravity on a Planet ↳ The strength of gravity (g) on the surface of a planet is given by g=M/r² ↳ M = mass of the planet ↳ r = radius ↳ More mass = more gravity ↳ If the mass of a planet were twice that of another (A is =) -> gravity is 2x as strong ↳ Larger separation = less gravity ↳ If the radius of a planet were twice that of another (A is =) -> gravity is 1/4 as strong ↳ Mars has 10 mass of Earth & 1/2 the radius ↳ g= 10/ (1/2)² = 10/ 1/4 = 40 -> Surface gravity on Mars is 4/10 of Earths Newton's Universal Law of Gravitation ↳ Calculates the force of gravity between all objects ↳ Fg=GM₁M₂/d² ↳ M₁, M₂ = mass of the objects ↳ d = distance between the objects Seasons/Day & Night ↳ Day & night is caused by the rotation of the Earth on its axis ↳ Sun appears to rise in the east & set in the west ↳ One revolution around the sun = one year ↳ Seasons ↳ Tilt of the Earth's axis causes seasons (23°) ↳ Has nothing to do with the distance from the Sun ↳ North tilts towards the Sun -> Northern summer, Southern winter ↳ North tilts away from the Sun -> Northern winter, Southern summer ↳ Northern hemisphere calendar ↳ Winter (12/21) : nights > days ↳ Spring (3/21) & Fall (9/21) : nights = days ↳ Summer (6/21) : nights < days ↳ No tilt = no seasons ↳ Increased tilt = more extreme seasons Moon Phases/Eclipses ↳ Revolution around Earth "approx 30 days ↳ Phases are caused by the Sun lighting up different parts of the Moon [Diagram with the following elements:] SUN [Purple curved line] EARTH [Moon phases labeled around Earth, including New Moon, Waxing Crescent, First Q Moon, Waxing Gibbous, Full Moon, Waning Gibbous, Third Q Moon, Waning Crescent] ↳ Moon rises 6 hours before overhead & sets 6 hours later ↳ EX: Full moon rises at 6pm, overhead at 12am & sets at 6am Eclipses ↳ Solar eclipse: moon is blocking the Sun's light ↳ Only occurs during a new moon ↳ Lunar eclipse: Earth's shadow passes across the moon ↳ Only occurs during a full moon ↳ Eclipses don't occur every month because the moon orbits in a slightly different plane than Earth orbits the Sun Mars' Moons ↳ Phobos ↳ possibly an astroid ↳ slow, fast orbit (revolves 3 times a day) -> leads to regular eclipses ↳ Deimos ↳ further orbit CONSTELLATIONS ↳ Constellations: large defined areas of the sky ↳ Anything visible in the region is "in" that constellation ↳ 88 constellations ↳ Stars in the same constellation can be at very different distances ↳ Different constellations are visible at different times of the year ↳ Ecliptic: the apparent path of the Sun over the course of a year, with respect to the distant stars ↳ Also refers to the plane in which Earth orbits the Sun ZODIACs ↳ 12 or 13 constellations that lie along the ecliptic ↳ Sun is inside a Zodiac constellation at all times ↳ Each one for about a year ↳ Winter zodiac constellations = ones opposite the Sun in the winter ↳ Summer zodiac constellations = ones opposite the Sun in the summer ELECTROMAGNETIC RADIATION/LIGHT ↳ Light has some properties of a wave & other properties of a particle ↳ Photon: a light "particle" ↳ Forms of light ↳ Gamma ray (highest energy) -> X-ray -> Ultraviolet (UV) -> visible -> infrared (IR) -> microwave -> radio (lowest energy) ↳ High energy light = high frequency = short wavelength = bluer color ↳ Low energy light = low frequency = long wavelength = redder color ↳ All forms of radiation travel at the speed of light Radio wavelengths: meters/centimeters ↳ Vis light wavelengths: ten billionths of a meter (hundreds of nanometers) ↳ X-ray wavelengths: nanometers/picometers ↳ Prism splits light into different colors by bending different wavelengths by different angles ↳ Think Dark Side of the Moon album ↳ The color we see is the color reflected ↳ Blackbody Spectrum: higher temp = more total light & a peak intensity at a shorter wavelength ↳ Sun's surface temp: 5800°K. ~peaks in the visible light region (around green) ↳ Room temp: 300°K -> peaks at IR region ↳ Visible & radio waves get through the atmosphere SPECTROSCOPY ↳ Types of spectra ↳ Continuum Spectrum: light at all wavelengths ↳ Absorption Spectrum: Shows absorption lines ↳ Dark lines in the spectrum at certain wavelengths, superimposed on a continuum spectrum ↳ Produced by a less-energetic gas cloud in front of a light source ↳ When electrons in atoms absorb photons & remove light of specific energies from the spectrum -> electrons move from a lower to a higher energy level ↳ Emission Spectrum: Shows emission lines ↳ Bright lines at specific wavelengths, in an otherwise empty (dark) spectrum, due to emission of photons from atoms in gas that have electrons 1 in elevated levels 2 ↳ Electrons jump from higher to lower energy levels ↳ Different chemical elements have different energy levels that their electrons can occupy