Midterm 1

• Humans first appear in the cosmic year


  December 31
• How we see planets in our solar system


  They reflect sunlight
• What allows astronomers to look into the universe's past


  The light-year (the finite speed of light)
• The assumption that the laws and constants of nature are the same everywhere and at all times allows us to have the science of astronomy
• The most important feature of a scientific hypothesis


  That it is testable (if it is found 'incorrect' it is discarded or altered; if it is found 'correct' over and over again, it graduates to a theory)
• A scientific law describes an observable occurrence in nature that appears to always be true
• Why the ancients believed the earth was a sphere


  • It casts a round shadow on the moon
  • You see the different stars in the sky if you move north or south
  • Other objects in the heavens are spheres
• Parallaxes of stars were not observed by ancient astronomers because stars are too far away to observe parallax with the unaided eye
• The main difference between the geocentric and the heliocentric models of the universe

  The sun is at the center (vs the earth)
• Evidence for heliocentrism over geocentrism


  • Moons of Jupiter - showed that not everything circled the Earth
  • Phases of Venus - was proof that the sun was at the center
• Although the Copernican system was largely correct to place the sun at the center of all planetary motion, the model still gave inaccurate predictions for planetary positions because it assumed circular orbits (we now know the planet orbits are ellipticals)
• The 18-degree-wide belt the sun and the planets travel through

  The zodiac
• Why astrology is considered inaccurate


  • Statistical tests showed that people are randomly distributed in their astrological characteristics
  • No known forces explain why the positions of the planets affect personality or fate
  • The dates that correspond to a modern person's sun sign have shifted significantly since the first astrological charts were made
• Newton combined the observations and rules assembled by Galileo, Brahe, and Kepler to formulate his laws of gravity and motion
• A body moving in a perfectly circular path at constant speed is being acted upon by an external force
• Earth has more mass than Mars


  The Earth spacecraft is moving faster than the Mars spacecraft
• Planet A orbits Star A with a period of 1 year and at a distance of 150 million km, and Planet B orbits Star B with a period of 2 years and also at a distance of 150 million km


  Star A has greater mass than Star B
• If the earth had 10 times its present mass but the same volume, your weight would change by a factor of 10 times greater
• If the distance between 2 bodies is quadrupled


  The gravitational force between them decreases by a factor of 16
• If the distance between two objects is increased


  The force of gravity between them decreases by a factor of x2
• If a satellite's orbit around Earth is increased, its orbital velocity decreases
• The difference between electromagnetic waves and other types of waves

  They don't need a medium to travel through
• What distinguishes one type of electromagnetic radiation from another

  Its wavelength
• The wavelength of maximum intensity, λmax, for Star A is longer than the wavelength of maximum intensity of Star B


  Star B has the greater temperature
• How an electron jumps from a lower energy level to a higher energy level in an atom

  By absorbing a photon
• Element spectrums


  • All rainbow = continuous
  • All black with colored lines = emission
  • Rainbow with lines of black = absorption
• A star with a redshifted spectrum is moving away from earth
• Budget increases mean that a university can build a telescope with a mirror that's 3 times larger than they had originally planned


  The new telescope will be able to collect 9 times more light than the previously planned one
• 3 basic components of a modern astronomical instrument


  • Mirror
  • Spectrometer
  • Detector
• One advantage of radio astronomy over visible light astronomy


  You can make observations during the day and night
• Astronomers place telescopes in Earth's orbit so they can observe light that doesn't penetrate Earth's atmosphere