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Objective 4 1 Objective 4: Describe techniques for gathering information about celestial bodies in the universe This objective is further broken down into 3 outcomes Outcome 4A: Explain the operation of optical telescopes Outcome 4B: Explain the role of spectrometers (spectroscopes) in determining characteristics of stars Outcome 4C: Explain the role of radio telescopes in determining characteristics of stars and star systems and describe space probes Outcome 4A: Explain the operation of optical telescopes Telescopes Look up at a clear, cloudless night sky and you can see a few thousand stars. With binoculars, you would see thousands more. Use a telescope and millions of stars will be revealed. Use one of the most powerful telescopes available and billions of stars come into view. Telescopes allow us to see fainter and more distant objects in detail that cannot be detected by the unaided eye. Two types of telescopes are described in this section. Both provide us with a variety of information about the objects that make up our universe. Optical telescopes Optical telescopes have been in use for the past 400 years. Think of optical telescopes as "light collectors." That is what their series of lenses and mirrors do: gather and focus the light from stars so that we can see it. The larger the area of the lenses or mirrors in a telescope, the greater the ability of the telescope to see the faint light of objects that are very distant. Optical telescopes CANNOT be used during the day, as the light in the atmosphere is brighter than the light from the stars. There are two types of optical telescopes: o Refracting telescopes: The first telescope ever designed was a simple refracting telescope. Refracting telescopes use two lenses to gather and focus starlight. The lens that light goes through first is called the primary (objective) lens. There is a limit to how large the lens in a refracting telescope can be. Any diameter over 1 m causes the glass in the lens to warp under its own weight. Trying to see through a lens when that happens would be like trying to make out details of the Moon by looking through the bottom of a pop bottle. Objective 4 2 o Reflecting telescopes: Reflecting telescopes use mirrors instead of lenses to gather and focus the light from stars. At one end of a reflecting telescope is a large concave mirror (called the primary, or objective mirror), which is made from glass-like material that is coated with a thin layer of metal. The metal, such as aluminum, is polished to a shiny finish so that it can reflect the faintest light it receives. Mirrors can be made much larger than lenses, which is why reflecting telescopes can be made to see farther into space than refracting telescopes. In addition, many mirrors can be put together to form one huge primary (objective) mirror. The Canada-France-Hawaii observatory has a huge 3.6 meter mirror as a primary mirror which is actually many smaller mirrors put together. The largest mirror used in a reflecting telescope is over 12 meters large. The Hubble space telescope Although remote mountains make excellent sites for building and operating telescopes away from light pollution and air pollution, astronomers are still at the mercy of the weather. Clouds, humidity (moisture in the air), and even high winds can interfere with star-gazing. The development of the Hubble Space Telescope offers a solution to these problems. Orbiting about 600 km above Earth, the Hubble Space Telescope (which is a reflecting telescope) uses a series of mirrors to focus light from extremely distant objects. Launched in 1990, the Hubble is cylinder-shaped, just over 13 m in length and 4.3 m in diameter at its widest point. Each orbit that the Hubble makes around Earth takes about 95 min. Even though the primary mirror of the Keck telescope in Hawaii is larger, Hubble can see farther and clearer than Keck or any other Earth based telescope because the atmosphere doesn’t disturb the light reaching Hubble in any way. Objective 4 1. The basic function of optical telescopes is to act as light - - collectors 2. Why can’t optical telescopes be used during the day? Light in atmosphere too bright 3. What happens as you increase the size of lenses and/or mirrors in optical telescopes? 3 6. Why can reflecting telescopes be built to see farther into space than refracting telescopes? Mirrors can be made much larger than lenses 7. Even a mirror has a limit to how large it can be. What can be done to make the objective mirror of a reflecting telescope larger than the maximum size limits of one single mirror? Put many mirrors together to form one huge mirror You can see further 4. Indicate what type of telescope is seen below and label the two parts indicated. 8. What are 5 things that can interfere with images viewed through an Earth based telescope? Air pollution, light pollution, clouds Humidity, wind Use the following information to answer the next question 5. Indicate what type of telescope is seen below and label the three parts that are pointed to. Then draw how light from the star would travel through the telescope 9. Which of the 4 telescopes above (A, B, C, or D) is mostly likely to take the clearest image? EXPLAIN WHY D-No atmosphere to distort images - 10. What type of telescope is the Hubble space telescope? Reflecting - Objective 4 4 Outcome 4B: Explain the role of spectrometers (spectroscopes) in determining characteristics of stars Determining star composition Now that astronomers could gaze deeper into the universe using simple telescopes, they faced a new challenge — the stars. Galileo had seen the stars through his telescope, but what were they made of? The spectroscope was one important technological advance that helped us learn more about the stars. Isaac Newton passed a beam of light through a prism to produce a spectrum of colors. If you pass the light through a narrow slit before sending it through a prism (which is found inside spectroscopes), the resulting spectrum will contain all the colors. The light from any light source can be split so the colors within that light source can be individually seen (see diagram above or diagram below on the left). Joseph von Fraunhofer used a spectroscope to observe the spectrum produced by the Sun, but he noticed dark lines in the spectrums of light throughout the solar system, called spectral lines. He didn’t know what they meant but the answer was discovered 50 years later when two chemists used a spectroscope to observe various chemicals when they were heated. The two scientists found that each particular element had its own unique spectral lines and would absorb certain parts of the color spectrum if light were to pass through them (see the diagram below on the right). Objective 4 5 What the above information lead to is the fact that the composition of stars millions of light years away could be determined (composition means what something is made of). The star emits light and the light passes through the star’s own atmosphere, which is made up of various gases. Certain parts of the light spectrum will be filtered out as the gases in that stars atmosphere filter out (absorb) those parts of the spectrum. Because we know which elements will filter out specific parts of the spectrum, we can determine stars’ compositions by analyzing the black-line fingerprints of the spectrum that reaches us here on Earth. We know that hydrogen is the main component of all stars with helium being the second main component, so the spectrum from all stars will have the blackline fingerprints of hydrogen and helium. Other elements can be found in some stars but not others, and their presence can be determined by the presence of an element’s unique blackline fingerprints. The diagram to the right shows how to determine a star’s composition based on the known black-line fingerprints of known elements. You just have to match up the black-line fingerprints of a star’s spectrum with the blackline fingerprints of known elements. Objective 4 6 Determining star motion Johann Doppler is famous for discovering what became known as the Doppler Effect. You hear it all the time when an ambulance with its siren going drives past. The diagram to the right shows it well. When a train blowing it’s whistle while it is motionless (diagram 1 to the right), a person behind it and a person in front of it will hear the same sound. But, if the train is moving forward (diagram 2 to the right) it compresses the sound waves it emits in front of it and stretches them out behind it. As a result the person in front hears a higher pitched noise than the person behind. Interestingly the same thing happens with light (which also travels in waves). You may remember from grade 8 that each color has a different wavelength, with the blue end having higher frequency waves, and the red end having lower frequency waves (see diagram A to the right). When a light emitting source, say a star, is moving away from us the light waves are slightly lengthened and as a result the light looks redder. This is called red shifting. When a star is moving toward Earth, the light waves are slightly shortened and as a result the light looks bluer. This is called blue shifting. Red shift and blue shift is measured by observing the spectral lines of the light from stars. In diagram “B”, star “x” is motionless when compared to Earth. Star “y” is moving away from Earth, as the spectral lines are shifted towards the red end. Star “z” is moving towards Earth, as the spectral lines are shifted towards the blue end (a trick to remember this that the Earth is blue, and stars moving towards Earth have spectral lines shifted towards the blue end). One last note: The greater shift you see of the spectral lines, the faster the star is moving either toward or away from Earth. Objective 4 11. What does a spectroscope do? Separates light into all it’s colors 12. When light from a glowing substance passes through a gas, what does that gas do to the light? Absorb certain parts of the spectrum 7 17. The dot below shows a police car moving. Draw a line in the direction the car is moving and draw a person where he/she would be hearing a lower pitch sound Explain why a lower pitch sound would be heard at this location Sound waves lengthened which we hear as a low pitch Use the following information to answer the next question 18. A shift towards the – RED - end of the spectrum 13. Think for yourselfWhat would cause the light in indicates a star or star system is moving away from spectrum B to have more lines than the light in Earth. A shift towards the – BLUE - end of the spectrum A? spectrum indicates a star or star system is moving towards Earth. The light from “B” passed through more types of gases Use the following information to answer the next question 14. Why are spectral lines present when we separate the incoming light from stars into a spectrum Gases present in the star’s atmosphere absorb (filter out) certain parts Use the following information to answer the next question 19. Is star C moving away or towards Earth? What about B? C: Toward B: Away Use the following information to answer the next question 15. What gases are present in each of the stars? Star 1 Star 2 Hydrogen, Helium, Calcium All of them 16. What two black-line fingerprints will show up in the spectrum of ALL stars. The ones of hydrogen and helium - 20. Above is the spectrum for the stars of Vega and Sarir. Are they motionless, moving away, or moving towards Earth? Which one is moving the fastest? -Toward -Sarir 21. By studying the spectrum of stars, scientists can determine a stars A. Mass and movement B. Mass and distance from Earth C. Composition and movement D. Composition and distance from Earth C - Objective 4 8 Outcome 4C: Explain the role of radio telescopes in determining characteristics of stars and star systems and describe space probes Radio telescopes What are radio telescopes and what are their advantages Light isn’t the only kind of radiation coming from the stars. In the late nineteenth century, scientists found out that light is just one form of electromagnetic radiation. Other forms include radio waves, infrared waves (heat), ultraviolet waves, X-ray waves, and gamma ray waves. The diagram to the right shows the entire spectrum of electromagnetic radiation. Notice that light waves (which can be seen with optical telescopes) occupy only a small portion of the spectrum. But celestial objects such as stars emit many other types of radiation, including radio waves which we will focus on in this outcome. Studying radio waves emitted by objects in space gives astronomers data that are not available from the visible spectrum. Radio waves are received from stars, galaxies, nebulae, black holes, and even some planets—both in our own solar system and in others. These signals are mapped through the use of sophisticated electronics and computers. With the development of radio telescopes, astronomers gained several advantages over optical telescopes. Radio waves are not affected by weather and can be detected during the day and at night. They are also not distorted by clouds, pollution, or the atmosphere as are light waves. Furthermore, by focusing their radio telescopes on certain areas of space that appear empty, astronomers have discovered additional information about the composition and distribution of matter in space—information that cannot be detected by optical equipment. For example, although hydrogen outside of stars emits no light, it does emit energy at a specific wavelength in the electromagnetic spectrum. Using radio telescopes, astronomers have been able to map the distribution of hydrogen in the Milky Way galaxy. This is how they learned that the shape of our galaxy is a spiral. Radio waves have wavelengths that are millions of times longer than light waves, meaning that these waves give less resolution, but can penetrate dust clouds in the galaxy, where light waves cannot. They can also go right through clouds not to mention materials like wood, brick and cement (this is why you can get radio reception almost anywhere). Radio waves can also be picked up during the day so scientists can work at any time (optical telescopes can only be used at night.) Having such large waves requires a large object to read these waves. To the right is a radio telescope found in Arecibo, Puerto Rico that has a diameter of more than 300 meters. Radio telescopes are typically made of metal mesh and resemble a satellite dish. What do radio telescopes detect? Radio telescopes cannot “see” radio waves or anything else. Radio waves are not in the visible light spectrum so there is nothing to see. In the early days of professional radio astronomy the movement of dials and needles monitored the incoming radio waves. The needle is similar to the kind you see in a voltmeter or even the speedometer of a car. The needles would jump around as strong radio waves were picked up. Astronomers then graphed the data. Today, computers can provide an artificial image which uses color codes for the strength of radio waves. The image to the right shows radio waves being picked up from a galaxy. Black means no radio waves are picked up, but as the shades/colors get lighter, this represents an increase of radio wave emission from objects within the galaxy. Objective 4 9 Space probes Telescopes, optical or radio, cannot provide answers to all the questions we have about our solar system. Often it is necessary to send the observation equipment right to the object so that tests not possible to conduct by telescope can be done. In the past several decades, astronomers have done just that, sending numerous space probes to explore distant areas of our planetary neighborhood. Space probes are unmanned devices which go to planets (other than Earth) or other celestial objects (comets, asteroids, ect…) to make observations of them. When a device takes observations of Earth we call the device a satellite (more specifically a remote sensing satellite), not a probe. When a device takes observations of other planets, asteroids or other celestial bodies we call the device a space probe. Some probes fly by celestial bodies and take pictures, some will be put in an orbit of celestial bodies and become a satellite for them, while others actually land on celestial bodies and make observations such as analyzing the soil. All probes are unmanned. A probe was sent to Mars in 2004 that sent back many images of the Mars landscape including pictures which show that water once flowed on Mars. 22. Why do you think that some scientists say that optical telescopes give them a very limited amount of information about space? Visible light is such a small part of the electromagnetic spectrum 26. Besides picking up radio waves and not being affected by atmospheric conditions, what is another advantage of using radio telescopes over optical telescopes? Can be used during the day 27. Why must radio telescopes be so much larger than 23. Circle the part of the electromagnetic spectrum that radio telescopes will be able to detect. Draw a box optical telescopes? Radio waves millions of times as large around the part that can be detected with optical telescopes (refracting or reflecting telescopes) as light waves 28. If radio waves can’t be seen, how do scientists know the strength of radio waves coming from various objects in space? 24. What kinds of objects emit radio waves? Stars, galaxies, nebulae, black holes Computers provide artificial image using color codes 29. Explain what a space probe is 25. Optical telescopes are built in specific areas on the Unmanned objects sent to celestial Earth. Good areas have lots of clear weather and low objects to make observations of them pollution. This is because clouds, rain, snow, pollution, 30. Which of the following do space probes NOT do? dust and various other things can easily block light. A. Fly by celestial bodies and take pictures Therefore, areas like Great Britain which get a lot of B. Send astronauts to celestial objects for rain is not an optimal place for optical telescopes. observation However, radio telescopes are found in many areas of C. Take pictures of Earth Earth including Great Britain. Why can radio D. Orbit celestial bodies such as planets or telescopes be put almost anywhere? asteroids. Radio waves not affected by E. Land on foreign celestial bodies F. There are 2 things above that space probes do atmospheric conditions like light waves not do are F Objective 4 - 10 Objective 4 11 Activity book created by Devon Rossington Vincent Massey School