Study Terms for Exam 1 in Astro 101

Term Definition
Astronomical Unit (AU) Earth's Average Distance From The Sun. (~ 150 million kilometers/ 93 million miles).
Constellation A region in the sky with well defined borders.
Asterism Small portion of a constellation (ie; the teapot in Sagittarius).
Lunar Eclipse Occurs when EARTH is directly between the Sun and the Moon and Earth's shadows falls onto the MOON.
Solar Eclipse Occurs when the MOON is directly between the Sun and the Earth and it's shadow falls into the Earth.
Phases of the Moon (8 phases). New, Waxing Crescent, First Quarter, Waxing Gibbous, Full, Waning Gibbous, Third Quarter, Waning Crescent.
Circumpolar Star that remains perpetually above the horizon, circling (counter-clockwise) around the North Celestial Pole each day.
Retrograde "Backwards". Period when planets reverse course and move backwards through westward through the zodiac rather than eastward.
Saros Cylcle The period over which the basic pattern of eclipses repeats. Happens about every 18 years and11 1/3 days.
Age of the Universe 14 Billion years old.
Age of the Solar System 4.6 Billion years old
Age of Planet Earth 4.5 billion years old.
Conservation of Angular Momentum Mass x Velocity x Distance. Angular momentum is a measure of the momentum of an object around an axis
Lightyear Distance that light can travel in one year. (~ 10 trillion km/ 6 trillion miles.)
Big Bang The event that created the universe.
Hypothesis A proposed explanation made on the basis of limited evidence as a starting point for further investigation.
Temperature The degree or intensity of heat present in a substance or object, especially as expressed according to a comparative scale.
Leaning Tower of Pisa Galileo used the tower to drop two cannonballs of different masses to demonstrate that the speed of the descent was independent of their masses.
Stonehenge Served as an astronomical device and helped mark the seasons. Built in stages between 2750 BC and 1550 BC
Composition of the Sun Made of mostly Hydrogen and Helium with small percentages of Oxygen, Carbon, Neon and Iron
Library of Alexandria Founded in Alexandria by a successor of Alexander the Great in 3rd century BC. Most famous for being destroyed and losing large amounts of information,
Redshift A shift toward longer wavelengths of the spectral lines emitted by a celestial object that is caused by the object moving away from the earth.
Blueshift The displacement of the spectrum to shorter wavelengths in the light coming from distant celestial objects moving toward the observer.
Edwin Hubble Namesake for the Hubble Space telescope. Known for showing that the recessional velocity of a galaxy increases with its distance from the earth, implying the universe is expanding
Mt. Wilson Astronomical observatory in Los Angeles County, California, United States. Located on a 1,740-meter peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles.
Equinox Occurs on the only two days of the year where the sun rises precisely east and sets precisely west. ("Equal Night").
Solstice The day that the Sun rises as far to the Northeast as it ever does, and sets as far to the Northwest, or rises are far to the South as it ever does, and sets as far to the Southwest.
Seasons Caused by the axis tilt and the orientation of the axis relative to the Sun's changes over the course of each orbit.
Nuclear Fusion A nuclear reaction in which two or more atomic nuclei come close enough to form one or more different atomic nuclei. This is how stars are made.
Location in the Galaxy In the milky way galaxy, midway from the center.
Erastosthenes Accurately estimated the circumference of the Earth.

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