Explore the Sun: Analyze Sunspots and Coronal Mass Ejections

Lab 3: The Sun OBJECTIVES This lab will help you to: 1. Determine the size of sunspots 2. Determine the rotation period of the Sun. 3. Study some images of Coronal Mass Ejections from the sun. Marketable Skills: This course assesses the following Core Objectives. In this assignment, you will develop the following marketable skills: Critical Thinking  Analyze Issues  Anticipate problems, solutions, and consequences.  Apply knowledge to make decisions  Detect patterns/themes/underlying principles  Interpret data and synthesize information Communication  Summarize information  Use proper technical writing skills Personal Responsibility  Accept responsibility  Exhibit Time Management  Show attention to detail  Learn and grow from mistakes Empirical Quantitative  Communicate results using tables, charts, graphs  Contextualize numeric information/data  Demonstrate logical thinking  Draw inferences from data, use data to formulate conclusions EQUIPMENT 1. Metric ruler with centimeter markings 2. Calculator 3. Do not take print out of images on pages 11 – 23! 1

INTRODUCTION Ever since Galileo saw sunspots on the surface of the Sun with his telescope, we have been intrigued by these “freckles” and their study has helped us to determine many properties of the Sun. In the last few decades, astronomers have developed some fantastic tools, one of which is SOHO, the Solar and Heliospheric Observatory. This is a 2-ton spacecraft located between Earth and Sun, about 1.5 million kilometers from earth. It continuously “looks” at the Sun and its many instruments have beamed back a tremendous amount of information since its launch in 1995. The cameras on SOHO capture many different types of images, which you will use in this experiment. The photosphere is the yellow surface of the Sun we see. While Galileo and others like Thomas Herriot of England recorded sunspots after 1611, historical records from Chinese astronomers indicate they were also aware of this phenomenon. However, sunspots are very small, and because it is dangerous to look at the Sun for long periods of time, we must use special precautions for viewing it. We can use specially filtered solar telescopes or make a special device with a pinhole, lens, and mirrors to “project” the sun’s image onto a piece of paper. The latter is a relatively simple way to view the Sun safely, and we have a special device to do this conveniently on campus. You must NEVER focus a telescope or binoculars on the Sun! These devices work by concentrating light to produce a sharp image. In the case of the Sun, the concentrated light can melt the glue holding the lenses in place and destroy the telescope or binoculars. More dangerously, the concentrated light can permanently damage the retina in your eyes. For these reasons, it is very important to view the Sun safely. Simply using dark glasses especially during eclipses is not enough. A total solar eclipse is a particularly fantastic sight and a great opportunity to study some features of the Sun. During a total solar eclipse, the Sun, Moon, and Earth all lie in the same plane, with the Moon between the Sun and Earth. By coincidence, the Sun is 400 times bigger than the Moon, but it is also 400 times further away. This means they have the same angular size in the sky, about 0.5 degrees, and the size of the Moon’s disk is the same as the Sun. When they are lined up exactly, and the Moon is at the proper distance from Earth, the Moon’s disk can completely cover up the Sun. However, this condition lasts for less than 7.5 minutes and is visible from only a few places on Earth. This makes total solar eclipses rare events that can be frightening if you are not aware of what’s happening! Daylight gradually gives way to darkness, and you can actually see the Sun with a “bite” taken out of it. As the bite increases, the sky gets darker, stars become visible, and at “totality” you see a black circle surrounded by a ghostly white light. The black circle is the Sun covered up by the Moon, and the white light is the Sun’s corona, which is always there, but since its light is too dim, it is obscured by the brighter light from the photosphere. Since the Moon is moving, within a few minutes it will uncover the Sun, the corona will once again become invisible, the Sun’s bite will appear in the opposite direction, the sky will gradually brighten and in less than an hour, everything will go back to “normal”. Partial solar eclipses are not as dramatic, but still impressive to see. We encourage you to go the extra mile to view an eclipse if you get the opportunity. But you must take special precautions to view all solar eclipses. Since the Sun’s light is diminished, it causes the pupils in 2

our eyes to dilate and there is a greater risk of retinal damage. Hence it is very important NOT to look directly at the Sun as the Moon creeps in. Special filters can be used to view the Sun safely and they are now available cheaply at eclipse sites. Keep April 8 th 2024, on your calendar when a total solar eclipse will be visible from some parts of U.S.A, including Dallas! Check out the eclipse path in your textbook and make plans to go view it – safely! Total Solar Eclipse on Aug 21 st , 2017; pictures taken by Prof. Anahita Sidhwa Modern solar telescopes use the same principle of a total solar eclipse to study the corona. The front end of the telescope is fitted with a filter that effectively covers up the disk of the Sun, so you see it as a black disk surrounded by the corona or the solar atmosphere. Some of the SOHO images that show a black disk in the middle, are using this principle to study areas outside the photosphere. While the rotation period of the Earth’s equator and poles is the same (24 hours) the Sun’s equatorial region rotates faster taking less time than the poles. When astronomers first saw sunspots, they speculated whether the black dots were other planets casting a shadow on the Sun. But Galileo soon decided these dots were on the Sun’s surface because they appeared to “flatten out” and look oval shaped when seen closer to the edge of the Sun. It is like sticking a quarter to a balloon. If you see it head- on, the quarter looks like a circle, but if you rotate the balloon and keep the quarter near the edge, it will look like an oval. The gas and plasma making up the Sun is a soup of moving charged particles which generate a strong magnetic field. The magnetic field lines get twisted as the equatorial regions move faster and, at some point, they push out of the photosphere and re-enter it, creating a very strong local magnetic field, which appears as a sunspot. The sunspot is dark because it is cooler than the surrounding gas, its temperature is about 4000 K compared to 5800 K for the surrounding 3

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