Astronomy 1. 10/17/17 - NASA JPL field trip 10/17/17 - LA Griffith Observatory field trip

Transcription

1 Astronomy 1 10/17/17 - NASA JPL field trip 10/17/17 - LA Griffith Observatory field trip

2 CH 1 Here and NOW Where do we fit in the Universe? How-small-we-really-are-in-this-universe

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4 Start here: The figure shows a region about 16 meters (52 feet) from the edge of the street to the door of this Building. Figure 1-1 p3

5 Each picture in the following sequence shows you a frame or field of view within the universe that is 100 times wider than the preceding picture.

6 In this figure, your field of view has increased in size by a factor of 100, and you can see an area 1.6 kilometers (1 mile) in diameter. Figure 1-2 p3

7 This figure has a span of 160 kilometers (100 miles).

8 At the next step in your journey, you will see the entire planet Earth about 13,000 km (8000 miles) in diameter The picture shows most of the daylight side. The blurriness at the extreme right is the sunset line. HW (Learning to look 1) In Figure 1-4 of the lecture the division between daylight and darkness is at the right on the globe of the Earth. How do you know this is the sunset line and not the sunrise line? Figure 1-4 p4

9 The rotation of Earth on its axis each 24 hours carries you eastward. As you cross the sunset line into darkness, you say the sun has set.

10 At the scale of this figure, the atmosphere on which your life depends is thinner than a strand of thread.

11 Enlarge your field of view again by a factor of 100, and you see a region 1,600,000 km (1 million miles) wide. Earth is the small blue dot in the center. The moon with a diameter of only about one-fourth that of Earth is an even smaller dot along its orbit.

12 If you had a high-mileage car, it may have made the equivalent of a trip to the moon which has an average distance from Earth of 380,000 kilometers (240,000 miles). These numbers are so large that it is inconvenient to write them out. 30 earths

13 Astronomy is the science of big numbers. You will use numbers much larger than these to describe the universe. Rather than writing out these numbers, it is more convenient to write them in scientific notation. This is nothing more than a simple way to write numbers without writing lots of zeros. For example, you would write 380,000 as 3.8 x 10 5.

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15 Enlarge your field of view again by a factor of 100, and you see a region 1,600,000 km = 1.6 x 10 6 (1 million miles) wide. Earth is the small blue dot in the center. The moon with a diameter of only about one-fourth that of Earth is an even smaller dot along its orbit.

16 When you once again enlarge your field of view by a factor of 100, Earth, its moon, and the moon s orbit all lie in the small red box at lower left. This figure has a diameter of about 1.6 x 10 8 kilometers.

17 Now, you can see the sun and two other planets that are part of our solar system. Our solar system consists of the sun, its family of planets, and some smaller bodies such as moons, asteroids, and comets. Like Earth, Venus and Mercury are planets small, nonluminous bodies that shine by reflecting light. Venus is about the size of Earth and Mercury is a bit larger than Earth s moon. In this figure, they are both too small to be seen as anything but tiny dots.

18 The sun is a star a self-luminous ball of hot gas that generates its own energy. The sun is 110 times larger in diameter than Earth, but it too is nothing more than a dot in the diagram. Another way astronomers deal with large numbers is to define new units: The average distance from Earth to the sun is called the astronomical unit (AU) a distance of 1.5 x 10 8 kilometers (93 million miles). For example, you can say, the average distance from Venus to the sun is about 0.7 AU.

19 After just six steps, each enlarging by a factor of 100, you now see the entire solar system. Your view now is 1 trillion (10 12 ) times wider than in the first figure. The details of the previous figure are lost in the red square at the center of this figure. You see only the brighter, more widely separated objects as you back away.

20 The sun, Mercury, Venus, and Earth lie so close together that you cannot separate them at this scale. Mars, the next outward planet, lies only 1.5 AU from the sun.

21 In contrast, Jupiter, Saturn, Uranus, and Neptune are so far from the sun that they are easy to find in the figure. Light from the sun reaches Earth in only 8 minutes, but it takes over 4 hours to reach Neptune.* Pluto orbits mostly outside Neptune s orbit, but it is no longer considered a major planet. * See the definition of a light year

22 When you again enlarge your field of view by a factor of 100 (10 14 ) the solar system becomes invisibly small. The sun is only a point of light, and all the planets and their orbits are now crowded into the small red square at the center. The planets are too small and reflect too little light to be visible so near the brilliance of the sun.

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24 Nor are any stars visible except for the sun. The sun is a fairly typical star, a bit larger than average, and is located in a fairly normal neighborhood in the universe. Although there are many billions of stars like the sun, none is close enough to be visible in the figure.

25 The stars are separated by average distances about 30 times larger than this view, which has a diameter of 11,000 AU. It is difficult to grasp the isolation of the stars. If the sun were represented by a golf ball in New York City, the nearest star would be another golf ball in Chicago. How far is the nearest Star

26 Now, your field of view has expanded to a diameter a bit over 1 million AU. The sun is at the center, and you see a few of the nearest stars. These stars are so distant that it is not reasonable to give their distances in AU.

27 Astronomers have defined a new larger unit of distance the lightyear. One light-year (ly) is the distance that light travels in one year roughly km or 63,000 AU.

28 The diameter of your field of view in the figure is 17 ly. The nearest star to the sun, Proxima Centauri, is 4.2 ly from Earth. In other words, light from Proxima Centauri takes 4.2 years to reach Earth.

29 Although stars are roughly the same size as the sun, they are so far away that you cannot see them as anything but points of light. Even with the largest telescopes on Earth, you still see only points of light when you look at stars. Any planets that might circle those stars are much too small and faint to be visible.

30 In the figure, the sizes of the dots represent not the sizes of the stars but their brightness. This is the custom in astronomical diagrams, and it is also how starlight is recorded. Bright stars make larger spots in a photo or electronic picture than faint stars.

31 When you expand your field of view by another factor of 100, the sun and its neighboring stars vanish into the background of thousands of other stars. The field of view is 1,700 ly in diameter.

32 No one has ever journeyed thousands of light-years to look back and photograph the sun s neighborhood. So, this is a representative picture of a part of the sky that can be used as a reasonable simulation. The sun is faint enough that it would not be easily located in a photo at this scale.

33 Some things that are invisible in this figure are actually critically important. You do not see the thin gas that fills the spaces between the stars.

34 A cloud of gas and dust in space named Messier 78, so far away its light takes 1600 years to reach earth. This image was created by a private citizen, Igor Chekalin of Russia, in response to a worldwide contest sponsored by the European southern observatory (ESO) in Mr. Chekalin s prize was an all-expenses-paid trip to Chile to work with the astronomers using one of ESO s giant telescopes. p3

35 Although those clouds of gas are thinner than the best vacuum produced in laboratories on Earth, it is those clouds that give birth to new stars. The sun formed from such a cloud about 5 billion years ago.

36 If you expand your field of view by a factor of 100, you see our galaxy. A galaxy is a great cloud of stars, gas, and dust bound together by the combined gravity of all the matter.

37 In the night sky, you see our galaxy from the inside as a great, cloudy wheel of stars ringing the sky as the Milky Way. Our galaxy is known as the Milky Way Galaxy.

38 Of course, no one has photographed our galaxy. This figure shows a galaxy similar to our own.

39 Our sun would be invisible in such a picture. If you could see it, you would find it about two-thirds of the way from the center to the edge.

40 Our galaxy, like many others, has graceful spiral arms winding outward through the disk. You will learn that stars are born in great clouds of gas and dust as they pass through these arms.

41 The visible disk of our galaxy is roughly 80,000 ly in diameter. Only a century ago, astronomers thought it was the entire universe an island universe of stars in an otherwise empty vastness.

42 As you expand your field of view by another factor of 100, our galaxy appears as a tiny luminous speck surrounded by other specks. The figure includes a region 17 million ly in diameter. Each dot represents a galaxy.

43 Our galaxy is part of a cluster of a few dozen galaxies. You will find that galaxies are commonly grouped together in clusters. Some of these galaxies have beautiful spiral patterns like our own galaxy, but others do not.

44 The figure represents a view with a diameter of 1.7 billion light years by combining observations with theoretical calculations.

45 The sequence of figures ends here it has reached the limits of the largest telescopes on Earth. Our view with the largest telescopes does not extend as far as the region that would be covered by a figure 100 times larger than the figure.

46 A problem in studying astronomy is keeping a proper sense of scale. Remember that each of the billions of galaxies contains billions of stars. Many of those stars probably have families of planets like our solar system. On some of those billions of planets, liquidwater oceans and protective atmospheres may have sheltered the spark of life.

47 It is possible that some other planets are inhabited by intelligent creatures who share your curiosity, wonder at the scale of the cosmos, and are looking back at you when you gaze into the heavens.

48 Pale Blue Dot

49 Powers of 10 Powers of 10 video Size Comparison Giant Black Hole in NGC 1277 size of universe (Explains Parallax) ON 618 is a very distant and extremely luminous quasar technically, a hyperluminous, broadabsorption line, radio-loud quasar located near the North Galactic Pole in the constellation Canes Venatici. It likely contains one of the most massive known black holes, perhaps weighing in at 66 billion times the mass of the Sun

50 Scientific Method A common misconception in science is that science provides facts or "truth" about a subject. Science is not collection of facts; rather, it is a process of investigation into the natural world and the knowledge generated through that process. This process of investigation is often referred to as the scientific method and it is typically defined in many textbooks and science courses as a linear set of steps through which a scientist moves from observation through experimentation and to a conclusion as shown below:

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