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Astro test one

What are the Planets in order? Mars, Venus, Earth, Mercury, Jupiter, Saturn, Uranus, Neptune
Milkway part of the local cluster - small group of 40 galaxies that is 3 million ly in diamter
Lightyear Distance light travels in one year
Astronomical Unit 1AU is the average distance between the sun and the Earth. 50 million km,
PARSEC 3.26 ly
Degree Arc Minute 1 degree = 60 Arc Minutes
Degree Arc Second 1 arc minute = 60 Arc Seconds
Angstrm small size - size of atom
Nanometer 1 nanometer = 1 billionith of a meter
size of the Milkway 100,000 lightyears in diameter, 1000 ly thick
Rotation of the Earth: 23.5 degrees, 23 hours and 56 minutes for the earth to rotate once
Precession Earth spins like an axis on a top, but the suns gravity adds a tug, which results in the axis of the Earth rotating (or precessing) with a 26,000 year period. Thanks to precession, Polaris (the North Star) will not always be the North Star
Tilt of the axis The axial tilt of a planet determines its seasons
Celestial Sphere Useful model of the night sky, not real, but simply a tool for understanding. The sphere appears to rotate around the earth once a day, giving the impressions that stars rise and set
Zenith The points directly overhead on the celestial sphere
Nadir The point opposite the zenith on the CS
Celestial Pole North/south celestial pole is the points at which the stars appear to rotate
Celestial Equator An extension of the Earth’s equator expanded out to the surface of the CS
Ecliptic The ecliptic “belt” on the celestial sphere is tipped relative to the celestial sphere is tipped relative to the celestial equator due to 23.5 degrees inclination of the Earth’s rotational axis
June Celestial equator In June, the sun appears north of the celestial equator
December Celestial Equator In Dec., the sun appears south of the celestial equator
Equniox Twice a year, the sun appears on the celestial equator, called equinoxes
Solstice During the summer solstice the earth is tilted towards the earth so the top of the earth the sun never sets, opposite during winter solstice
Zodiac The band that lies 9 degrees on either side of the ecliptic on the celestial sphere - 13 zodiacal constellations: Aries, Leo, Libra, Cancer, Gemini, Orion, Taurus, Pisces, Aquarius, Capricorns, Sagittarius, Scorpios, and Virgo
Phases of the Moon From the earth, we see only potions of the illuminated surface, giving it the appearance of phases of the moon
Full Moon The earth is between the moon and the sun, so we see all of the illuminated surface
New Moon The moon is between the earth and the sun so we see none of the illuminated surface
Why every new or full moon does not produce an eclipse? In order for an eclipse to occur, the moon must lie directly between the Earth and the Sun (solar eclipse) or the Earth must lie directly between the Moon and the Sun (lunar eclipse)
First person to measure the Earth Eratosenthes, the sun could be seen from the bottle of a well in Syene, so the sun must be directly overheard. Then he measured the angle the sun made with the horizon in Alexandria, calculated a diameter of 13,000 km, which is almost exactly correct
Retrograde motion of planets When one planet takes over another, passing each other OR the direction opposite to the movement of something else
Geocentric Model Models in which everything revolves around the earth. From the earliest times, this kind of model was used to describe the heavens, did not explain retrograde motions
Heliocentric Model Model centered around the sun
Ptolemaic Cosmologic System Two commonly made observations supported the idea that the earth was the center of the universe—The stars, sun and planets appear to revolve around the earth each day and that the earth does not seem to move form the perspective of an earth boun, unmoving
Copernican Cosmologic System Retrograde is explained by the relative speed between two planets—when one planet overtakes another, retrograde motion is observed
Tycho Brahe to Astronomy Built instruments to measure the position of planets very accurately (~1 arc minute), found that comets moved outside the Earth’s atmosphere, as he could detect no parallax motion in the stars, planets around the sun, sun around the earth
Johannes Kepler Using Brahe’s data, discovered that the planets fo not move in circles around the sun, they follow eclipses with the sun at one of the two foci
Ellipse: Focus, semi-major and semi-minor axes Ellipse: Focus, semi-major and semi-minor axes: The shape of an ellipse is described by its semi-major and semi-minor axes (as described in Kepler’s First Law)
Speed of a planet when orbiting the Sun--- locations of highest and lowest speeds: Highest when near the sun, slowest when farther away from the sun
Keplers first law Planets moved in elliptical orbits with sun at one focus of the ellipse o Developed a heliocentric model o Did not agree with the ancients of Brahe o The shape of ellipse is described by its semi-major and semi-minor axes
Kepler’s Second Law orbital speed of a planet varies so that a line joining the sun and the planet will sweep out of equal areas in equal time intervals o Planets move faster when near the sun, slower when farther from the sun o Explained non circular behavior of planets
Kepler’s Third Law The amount of time a planet takes to orbit the sun (it’s period) P (years) is related to its orbit size, a, AU, by P2=a3
Kepler's Laws o Kepler’s Laws describe the shape of a planet’s orbit, its orbital period and how far from the Sun the planet is positioned
Inertia, Mass, and Force Mass is described by the amount of matter an object contains, different from weight—weight requires gravity or some other force to exist. Inertia is The tendency of a mass to stay in motion
Speed only magnitude
Velocity magnitude and direction, velocity is speed with direction
Acceleration The rate of change of velocity • Stepping on a gas pedal accelerates a car, it increases the speed • Stepping on the brakes decelerates a car, it decreases the speed o A change is an object’s direction of motion is also acceleration
Created by: kardokus