Name: Astronomy Unit Test Review Sheet 1. Describe how each of the following scientists contributed to Astronomy: a. Galileo- used a telescope to see craters, moons, etc b. Brahe- great observations but incorrect conclusions c. Kepler- Laws of planetary motion d. Newton- gravity explains why objects fall to the earth and why planets orbit the sun e. Hubble- proved the existence of other galaxies; classified galaxies f. Copernicus- Sun centered universe g. Ptolemy- Earth centered universe 2. What is an optical telescope? What is the difference between a reflecting and a refracting telescope? What other types of telescopes do scientists use to gather information? Optical telescopes are used to see visible light from far away. Refracting uses a glass lens and a reflecting uses mirrors. Scientists also use non-optical telescopes such as x-ray and UV telescopes to see invisible light. 3. What is a light year? Explain how it is used by scientists. A light year is the distance that light travels in one year. Scientists use it to measure the distance between objects in space. 4. List the 7 different types of electromagnetic radiation in order from shortest wavelength to longest wavelength. Which are most dangerous to humans? Why? Gamma rays, x-rays, UV light, visible light, infrared, microwaves, radiowaves Gamma rays are the most dangerous because they have the most energy. 5. Explain how constellations are used to organize the night sky. Constellations include both the region of the sky and the stars in that region. They are used in a similar way that states are used as a location for objects or places. 6. List the colors of stars in order from lowest temperature to highest temperature. Red (lowest temperature) → blue (highest temperature) 7. Compare and contrast apparent and absolute magnitude? Which is most useful to scientists? Apparent magnitude is the brightness a star appears from earth and absolute magnitude is the actual brightness if stars were all the same distance away. The absolute magnitude tells a scientist more about a star than the apparent magnitude. 8. What is another name for Polaris? Why was Polaris a useful navigation tool? Polaris is also known as the North star. It was used as a navigation tool because it does not move very much throughout the night. 9. Why do stars appear to be moving in a circle around Polaris? What type of motion is this? How do stars actually move? Many stars seem to move around Polaris as the Earth rotates. This is the apparent motion of stars. Stars are moving, but not in a circle. 10. What determines the lifecycle of a star? The life of a star depends on the mass of the star. 11. List the following types of stars from oldest to youngest: giant, supergiant, white dwarf, main sequence. Explain the temperature ranges and luminosity ranges for each. White dwarf (oldest) → giant/ supergiant → main sequence (youngest) ↓ ↓ ↓ Hot and bright cool but bright moderately hot and bright 12. How do scientists believe the universe was formed? An explosion called the big bang 13. How long does it take for the Earth to rotate once on its axis? How long does it take for the Earth to revolve around the sun? Day (24 hrs)- Earth rotates once 365.25 days – Earth revolves around the sun 14. Why do we experience different seasons at some parts of the Earth? The earth receives either direct or indirect sunlight as it revolves around the sun on a tilt. 15. When does the Northern Hemisphere receive the most direct rays from the sun? June (summer solstice) 16. What is the Big Bang Theory? A theory about how the universe began after a big explosion. 17. How does the sun generate energy? Explain this process. Nuclear fusion generates energy as hydrogen atoms combine to form helium atoms. 18. How long does it take for the moon to revolve around the Earth and repeat the same phase? Why do we see different phases of the moon from Earth? It takes about a month for the moon to revolve around the earth. We see different phases of the moon because we see different portions of the sunlit side of the moon as it orbits the earth. 19. List the 8 phases of the moon, starting with a New Moon. - New moon, waxing crescent, first quarter, waxing gibbous, full moon, waning gibbous, third quarter, waning crescent 20. What is a lunar eclipse? What is a solar eclipse? A lunar eclipse is when the moon is shielded by the shadow of the earth. A solar eclipse is when the sunlight reaching the earth is blocked by the moon. 21. Compare and contrast the 3 different types of galaxies? Spiral galaxies have concentrated centers and spiral arms. Elliptical galaxies have a concentrated circular or oval shape. Irregular galaxies have a shape unlike a spiral or elliptical galaxy. 22. What type of galaxy is the Milky Way galaxy? Spiral galaxy 23. What does an H-R diagram tell you about a star? Temperature and absolute magnitude (actual brightness) 24. Where on the H-R diagram would our sun be located? Diagonal pattern/ main sequence 25. For the Northern Hemisphere, when is the summer solstice? The winter solstice? Summer solstice = June 21st / 22nd Winter solstice = December 21st/ 22nd 26. Using terms like tilt, axis, and direct light, explain why June 21 is a significant date in the Northern Hemisphere. On June 21st, the earth is titled on its axis so that the Northern hemisphere is receiving the most direct sunlight. 27. Explain why the oceans experience high and low tides on Earth. How many tides will an area on Earth experience each day? What are Spring Tides and Neap Tides? When do they occur? The earth experiences high tides when that part of the earth’s oceans is pulled outward by the moon’s gravity. The part of the ocean where water flows away is where the low tides are. Spring tides are the greatest tides because the moon and sun’s gravity combine. A neap tide is the lowest tide because the moon and sun are at right angles from each other. Most places have 2 high and 2 low tides per day.