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PHY 1455 Exam #1

QuestionAnswer
Celestial Sphere An imaginary great hallow sphere surrounding the earth with stars attached to it. Its a way we identify the stars and where they are.
circumpolar star stars that never set from our position.
Polaris a fairly bright star really close to the North Celestial Pole
celestial equator n imaginary circle around the sky directly above the Earth's equator. It is always 90 degrees from the poles.
Declination The lines on a map of the Earth that run east-west parallel to the equator are lines of latitude that are projected onto the sky
Right Ascension The lines on a map of the Earth that run north-south are lines of longitude and when projected onto the sky
lunar eclipse the Sun-Moon angle is exactly 180 degrees and you see the Earth's shadow covering the Moon. Sun-earth-moon
solar eclipse the moon is in new phase and it is covering up the Sun. Earth-Moon-Sun
Annular eclipse A bright ring will be visible around the Moon when it is lined up with the Sun. (Solar)
Retrograde motion a planet will slow down its eastward drift among the stars, halt, and then back up and head westward for a few weeks or months, then halt and move eastward again
Constellations A way of mapping out the stars in the sky by a group of stars or area of the celestial sphere.
Zodiac Twelve 30 degree divisions on a narrow belt of constellations centered on the ecliptic. You can see one per month.
Total eclipse When the sun is completely covered by the moon because the umbra hits the earth.
Partial eclipse If the Moon only passed through the outer part of the shadow (the penumbra), then the observer on the Moon would see the Sun only partially covered up.
Why don't eclipses happen every month? The orbit of the moon is tilted
Zenith The point straight overhead on the celestial sphere for any observer and is always 90 degrees from the horizon
Ecliptic yearly path of the Sun through the stars
Vernal (spring) equinox When the sun on the ecliptic path intersects the celestial equator moving northward.
Autumnal (fall) equinox When the sun on the ecliptic path intersects the celestial equator moving southward.
Summer solstice when the sun is at the farthest northern point above the celestial equator.
Winter solstice When the sun is at the farthest southern point above the celestial equator.
How can you calculate the velocity of light? Frequency * wavelength
Wave nature of light In a vacuum all waves travel the speed of light
Azimuth how many degrees a star is along the horizon and corresponds to the compass direction
altitude how many degrees a star is above the horizon (anywhere from 0 to 90 degrees)
Nadir The point straight below on the celestial sphere for any observer and is always 90 degrees from the horizon
Horizon The point straight ahead on the celestial sphere for any observer.
Electromagnetic waves and examples in order. Long wavelength (RED) to shortest wavelength (BLUE) - Radio, infrared, visible, ultraviolet, x-ray,gamma-ray
Redshift the object is moving away from you, the waves are stretched out, so their wavelength is longer. The lines are shifted to longer (redder) wavelengths
Blueshift the object is moving toward you, the waves are compressed, so their wavelength is shorter. The lines are shifted to shorter (bluer) wavelengths
Blackbody an object that absorbs all the light falling on it, reflecting none of it, hence, it appears black. When the ``blackbody'' object is heated, it emits light very efficiently without any gaps or breaks in the brightness.
What is a spectrum of an object? The variation in the intensity of its radiation at different wavelengths
Absolute zero When the temperature is at its lowest (0 K) and there is no motion within the molecules
Kelvin temperature scale A natural scale for the temperature that at 0, its the absolute zero.
Wien's law The peak of the thermal spectrum in nanometers is related to the temperature (in K)
Stefan-Boltzmann law A small change in temperature produces a huge change in the amount of the energy emitted by every unit of the object.
What gives off a continuous spectrum? A hot solid, liquid or gas, under high pressure
What gives off a emission line spectrum? A hot gas under low pressure produces a bright-line
What gives off a absorption line spectrum (dark lines)? a source of a continuous spectrum is viewed behind a cool gas under pressure.
What do atoms and molecules existence depend on? Temperature and chemical composition
Who made up the spectrum laws? Kirchhoff
Doppler effect The wave nature of light means there will be a shift in the spectral lines of an object if it is moving
Aristotle He was most associated with the ancient greek world view
Aristarchus rejected the Geocentric world view and supported the Heliocentric view
Eratosthenes accurately determined the size of the Earth
Ptolemy Almagest
Geocentric model of the Universe Where the earth is at the center and things naturally move to the center of the Earth and the only way to deviate from that is to have a force applied to the object
Heliocentric model of the Universe Where the sun is at the center and the planets orbit around it.
Copernicus Invented the Heliocentric model of the Universe
Tycho Brache Last astronomer without a telescope and provided Kepler with the data he needed to create his three laws.
J. Kepler Creates the three laws of planetary motion
What is Kepler's first law? The orbit of a planet is an ellipse where one focus of the ellipse is the sun (Law of Ellipses)
What is Kepler's second law? A line from the planet to the sun sweeps out equal areas in equal amounts of time. (Law of Equal areas)
What is Kepler's third law? The period of a planet's orbit squared is proportional to its average distance from the sun cubed. (Law of harmonies; p^2 = a^3)
Gaileo Used a telescope and challenged the conventional wisdom of the motion of objects and the nature of the heavens
What did Gaileo found to challenge Geocentric model? Phases of Venus and Moons of Jupiter
What did Gaileo found to challenge the idea that the heavenly object was perfect? Sunspots and mountains on the moon
Newton Created the three laws of motion and universal law of gravity
What is Newton's first law? A body remains at rest, or moves in a straight line (at a constant velocity), unless acted upon by a net outside force. (Law of Inertia)
What is Newton's second law? The acceleration of an object is proportional to the force acting upon it. (F=MA)
What is Newton's third law? For every action, there is an equal and opposite reaction. (Law of Reciprocal Actions
Created by: atate92