3. Therefore, for your model to include the sun, you would need a ball about as big as

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1 Astronomy 170B1 M. Rieke & M. Halford CORRECT ANSWERS IN BOLDFACE Astronomers use various ways to understand large masses and distances, such as ratios and scientific notation. For example, if you are told that a jet airplane is 40 meters long, that might not register as well as being told that it is eight times as long as a car. The first part of this homework explores ratios and scientific notation. Let s try the same logic on the sizes of the earth and moon: The diameter of moon is 3,476 km The diameter of the earth is 12,756 km These numbers are too big to register in terms of everyday experience, but maybe we can make a scale model in our minds (like the one of the solar system in the first lecture). If we divide the diameter of the earth by that of the moon, we get Earth diameter Moon diameter km km Here, the two squiggly lines ( ) mean is approximately equal. That is, the earth is about four times wider than the moon, or for our model, we should use something four times smaller for the moon than for the earth. 1. Which would you pick for such a model? a.) a basketball and a soccer ball b.) a basketball and a baseball (hardball) c.) a basketball and a ping pong ball d.) a basketball and a pea e.) a basketball and a grain of salt 2. The distance from the earth to the moon is about 384,400km (this is the radius of the orbit of the moon, which is half of its diameter). This is about 30 times the diameter of the earth, so your model moon would be how far from your model earth? a.) the width of the lecture hall [about 30 feet] b.) the height of your chair c.) the height of the Administration building d.) the length of the campus The diameter of the sun is 1,392,000km. We then have Sun diameter km Earth diameter 12756km 3. Therefore, for your model to include the sun, you would need a ball about as big as a.) a large SUV is long b.) a two story house is high c.) a football field is wide [100 feet] d.) the UA campus from end to end e.) the distance to Phoenix

2 4.) Now, let s compare the diameter of the sun with the size of the moon s orbit around the earth, which is 769,000km in diameter. The ratio of the sun s diameter to the diameter of this orbit is about 2: Sun diameter km 2 Moon ' s orbit diameter km Does this mean that a.) two suns placed side to side would fit within the orbit of the moon, or that b.) two orbits of the moon would fit inside the sun? Volumes of spheres can be compared by comparing the cubes of the diameters. Therefore, the volume of the sun compared to the volume of the earth is 3 Volume of Sun km Volume of Earth 12756km 5. In scientific notation, this ratio is a.) 1 x 10 5 b.) 1 x 10 3 c.) 1 x 10 6 d.) 1 x In scientific notation, what is the ratio of the volume of the sun to that of the moon? a.)16 x 10 5 b.) 8 x 10 4 c.) 64 x 10 6 d.) 4 x 10 8 Looking at Distant Objects Imagine that you have just received four pictures of four different children who live near four of the closest stars to the Sun. Each picture shows a child on his or her 12th birthday. The pictures were each broadcast by radio directly to you on the day of the child s birthday. Note the abbreviation ly is used below to represent a light-year. Peter lives on a planet orbiting Barnard s Star, which is 6.0 ly from the Sun. Celeste lives on a planet orbiting Sirius, which is 8.6 ly from the Sun. Savannah lives on a planet orbiting Alpha Centauri, which is 4.3 ly from the Sun. Ron lives on a planet orbiting Procyon, which is 11.4 ly from the Sun. 7.) What is a light-year?. Is it an interval of time, a measure of length an indication of speed, or something else? Look at for some help on this section. a.) Interval of time b.) Measure of length c.) indication of speed d.) something else 8.) Which child lives closest to the Sun? a.) Peter b.) Celeste c.) Savannah d.) Ron 9.) What was the greatest amount of time that it took for any one of the pictures to travel from the child to you? a.) 11.4 years b.) more than 11.4 years c.) less than 11.4 years

3 If each child was 12 years old when he or she sent his or her picture to you, how old were the children when you received their picture? 10.) Peter a.) 12 years b.) 6 years c.) 18 years 11. Celeste a.) 12 years b.) 8.6 years c.) 20.6 years 12.) Suppose the children were issued intergalactic standard radio transmitters that have the same intrinsic output strength. Which one will have the strongest signal as you received it? a.) Peter b.) Celeste c.) Savannah d.) Ron 13.) Compare the signal from Celeste with that from Savannah. Which will be weaker? a.) Celeste b.) Savannah c.) they will be the same 14.) The telescope image at the right was taken of the Andromeda Galaxy, which is located 2.5 million ly away from us. Is this an image showing how the Andromeda Galaxy really is right now, how it was in the past or how it will be in the future? a.) right now b.) 2.5 million years in the future c.) 2.5 million years in the past Imagine that you are observing the light from a distant star that was located in a galaxy 100 million ly away from you. By analysis of the starlight received, you are able to tell that the image we see is of a 10 million year old star. You are also able to predict that the star will have a total lifetime of 50 million years, at which point it will end in a catastrophic supernova. 15.) How old does the star appear to us here on Earth? 16.) How long will it be before we receive the light from the supernova event? 17.) How many years ago did the supernova occur? 18.) Where on earth can you in principle see the largest number of different stars over the course of a year? a.) the north pole b.) the equator c.) the number of stars should not depend on where you are Look at ircamera.as.arizona.edu/astr2016/text/starmotions.htm

4 19.) March 20 will be an equinox. This means a.) the amount of sunlight reaching the northern and southern hemispheres will be the same on that day b.) the monsoon season will finish c.) Alaska will start having midnight sun 20.) When it is winter in Tucson, it is a.) winter all over the world b.) summer in Australia (southern hemisphere) c.) winter in Australia d.) spring in Australia e.) fall in Australia 21. How long does it take the Moon to rotate on its axis once? a.) the Moon does not rotate b.) 24 hours c.) 365 days d.) about 29 days Look at 22.) Our modern calendar a.) has been used for so long no one remembers where it came from b.) is largely the creation of the famous emperor of Rome, Julius Caesar c.) Is still not well tuned to the mismatch of the day to the year and will need adjustment soon d.) Was brought down unchanged from the Babylonian astronomers e.) Is based entirely on recent observations and concepts. 23.) a "blue moon" is a.) when the moon looks blue against the sky in the daytime b.) a new moon seen in the daytime, so the part of the disk of the moon not directly illuminated by the sun looks blue c.) the second full moon within the same month d.) the moon seen on a bitter cold winter night 24.) the "man in the moon" is a.) an arrangement of lunar features that can look like a human face b.) the body of an astronaut that was left there when there was an accident that killed him c.) just a face artists make up to make the moon look more approachable d.) a concept left from the Greek gods

5 25.) Scientists use facts a.) to support or to refute theories b.) only to support theories c.) only to refute theories 26.) Summer is hotter than winter because a.) the Earth is closer to the Sun b.) the Sun s output varies periodically on a time scale of a year c.) the tilt of the Earth s axis results in sunlight hitting the ground more directly in summer d.) of a the periodicity in the Earth s climate 27.) Ancient peoples built large structures to measure positions of astronomical objects to help them a.) show their superiority over other tribes b.) predict the seasons to assist agriculture c.) keep everyone employed d.) show off their architectural skills 28.) If tonight is a full moon, what will the moon s phase be in two weeks? a.) full b.) first quarter c.) last quarter d.) new 29.) What fraction of the Earth s surface can view a lunar eclipse? a.) half b.) a narrow strip c.) all of it d.) one quarter 30.) A solar eclipse occurs at which moon phase? a.) any b.) new c.) first quarter d.) full e.) last quarter