ASTR Midterm I

• The point directly over your own (observer's) head at any given time is the zenith.
• On the celestial sphere, halfway between the celestial poles lies the celestial equator.
• Why is the Half Moon not the name of a lunar phase?

  We only see the "near side" half of the moon from Earth, and only half of that half is illuminated.
• The celestial sphere turns once around each day because the planet on which we live is rotating.
• NOT a step in the process of getting a numerical answer using a math formula: dividing quantities/variables on left side of equal sign by right (or vice versa)
• The path the Sun appears to trace around the celestial sphere each year is the ecliptic.
• The 88 sectors into which astronomers divide the celestial sphere are constellations.
• The celestial sphere is not another name for our universe.
• A person who has done all their night sky observing at the Atacama Desert (Chile) hasn't seen the North Star/Polaris.
• A light year is the distance that light travels in one year.
• AU is not the biggest unit of length in astronomy.
• The Arecibo Observatory in Puerto Rico can give you wide coverage of the celestial sphere over a 24-hour period.
• In the angular size formula:

  • Numerator variable is always size of object
  • Denominator variable is always distance to location of object
  • Angular size must always be less than 360º for objects that aren't filling the sky
• The idea that planets travel in circular orbits is a misconception in all early models of the solar system (discussed in class).
• When it comes to our place in the solar system today, we accept a heliocentric model.
• Galileo discovered moons around Jupiter with his telescope that clearly refuted the geocentric model/theory.
• Kepler proposed that the orbits of the planets have elliptical shape.
• According to Kepler's 2nd Law, comets (eccentric orbits) should spend a lot more of their time far from the Sun.
• Kepler's 3rd law with Newton's modifications (P^2 [M1 + M2] = a^3), reduces to P^2 = a^3 when M1 represents the mass of the Sun and thus M2 is the mass of a Sun-orbiting celestial body.
• Newton's reformulation of Kepler's third law allows us to measure the masses of bodies in orbit around each other, if we can measure the distances between the bodies and periods of revolution.
• According to Kepler's 3rd law P^2 (M1) = a^3, a planet's mass has no effect on its orbit around the Sun.
• If the distance between two objects is tripled, the gravitational force (F = GM1M2 / R^2) exerted by one on the other will be nine times as much.
• The gravitational attraction between an object and the Earth extends to infinity.
• The "prime meridian" (longitude = 0) passed through Greenwich, England.
• You could see the same set of stars at night for as long as possible at the North or South Pole.
• If you want to locate someone precisely on the surface of the Earth, you specify their exact latitude and longitude. If you want to locate a star precisely on the sky, you need to specify its exact right ascension and declination.
• To stop our planet from having all the different seasons, you would have to change the tilt of Earth's axis.
• North American summers are hotter than winters because the Sun's rays hit the Earth more directly in the Summer and spread out less.
• The best time of day to look for the thinnest crescent moon you can find just after the new moon would be just as the sun is setting, or just after.
• In both New Zealand and South Africa, the days are shortest and the nights are longest in late June.
• The Sun also raises tides on Earth, but its effect is smaller than that of the Moon.
• The period of the moon's rotation on its axis is the same as its revolution around the Earth.
• If we observe a full moon tonight, we should wait a little over two weeks until the moon is in a waxing crescent phase.
• The full moon is at its highest point in the sky at roughly midnight.
• The Moon is up only during the night hours and all night long during the full moon phase.
• The distance between crests of a light wave is called the wavelength.
• All light travels through space at the same speed.
• Gamma rays have the highest frequency.
• Ultraviolet light causes sunburns on Earth.
• The main factor behind the specific color of visible light is the wavelength of the light.