Unit E Lesson 8: Tools used to Interpret Space
Completion requirements
Unit E Lesson 8: Tools used to Interpret Space
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Learning Targets |
Big Question: What tools are used to interpret space?
There are a variety of techniques, methods, and calculations that astronomers use to better understand the vastness of space.
There are a variety of techniques, methods, and calculations that astronomers use to better understand the vastness of space.
At the end of this inquiry, you should be able to answer the following questions:
- What are some of the early star instruments used for guiding man?
- When is an astronomical unit used?
- When is a light-year used?
- What is triangulation?
- When is parallax used?
- Why is Earth’s position every six months used as triangulation points in calculating a star’s distance?
- What is the use of a spectroscope?
- What is meant by the term red-shifted?
- What is meant by the term blue-shifted?
- How does the Doppler effect work?
- How is the Doppler effect used regarding space?
Pages 378 and 379, 402 and 403, and 446 to 453 in your textbook will help you answer these space tools questions.
Introduction
Using the Stars to Interpret Earth
For centuries, humans have used tools to observe and interpret the objects in the sky. Ancient Egyptians invented devices that would help them to create astronomical charts and predictions.
The merkhet (fig. 1) tracked the alignment of certain stars and a quadrant (fig. 2) measured the star’s height above the horizon.
For centuries, humans have used tools to observe and interpret the objects in the sky. Ancient Egyptians invented devices that would help them to create astronomical charts and predictions.
The merkhet (fig. 1) tracked the alignment of certain stars and a quadrant (fig. 2) measured the star’s height above the horizon.
Figure 1 – Merkhet
Figure 2 – Quadrant
Astrolabe
The astrolabe was invented in 150 BCE and was used by sailors, as well as astronomers, for navigation. The cross-staff or Jacob's staff aided in the measurement of distances and was used by sailors in the Middle Ages.
Using an Astrolabe
An astrolabe helped early astronomers to determine the altitude of objects in the night sky. If you'd like to try one yourself, you can use these online instructions to build one, or refer to pages 402 and 403 in the Science in Action textbook.
Figure 3 – An astrolabe (left) and a Jacob's staff (right).
Interpreting the Universe
Early technology helped astronomers and others to use the stars to understand Earth better. By calculating the movement of stars or the distances between stars, humans gained an understanding of the shape, movement, and place of Earth in the universe. Astronomers in ancient Greece, China, and Mexico used tools in combination with geometry to calculate the Earth's distance from the Sun. As technology and understanding of the Universe improved, researchers developed many instruments and strategies not only for capturing information about the Universe but also for interpreting and making sense of that information.
Early technology helped astronomers and others to use the stars to understand Earth better. By calculating the movement of stars or the distances between stars, humans gained an understanding of the shape, movement, and place of Earth in the universe. Astronomers in ancient Greece, China, and Mexico used tools in combination with geometry to calculate the Earth's distance from the Sun. As technology and understanding of the Universe improved, researchers developed many instruments and strategies not only for capturing information about the Universe but also for interpreting and making sense of that information.
Watch
Astronomical Distance
Watch the following video and read page 379 in Science in Action 9 to review the units used to measure distances in space. As you watch the video, consider the following questions. What is an Astronomical Unit? What is a light-year?
Watch the following video and read page 379 in Science in Action 9 to review the units used to measure distances in space. As you watch the video, consider the following questions. What is an Astronomical Unit? What is a light-year?
Triangulation and Parallax
Triangulation is a method of indirectly measuring distance by creating an imaginary triangle between an observer and an object. Pretend that we needed to know the width of a river without crossing the river.
Remembering that all angles in a triangle must equal 180º, we could calculate the distance using Euclidean Geometry and the law of sines.
However, because all angles in a triangle must equal 180º, we can calculate the distance without using geometry by recreating the triangle on paper.
Triangulation is a method of indirectly measuring distance by creating an imaginary triangle between an observer and an object. Pretend that we needed to know the width of a river without crossing the river.
- We can start by choosing a point on the riverbank exactly opposite an object such as a tree on the other side and creating an imaginary line.
- Then, we can use a protractor to measure a 90º angle.
- Using that angle, we measure a distance from our original viewpoint (A) to a new viewpoint (B).
- The distance between these two viewpoints is the baseline.
- At the second viewpoint (B), draw another imaginary line and calculate the angle created by the baseline and this line.
Remembering that all angles in a triangle must equal 180º, we could calculate the distance using Euclidean Geometry and the law of sines.
However, because all angles in a triangle must equal 180º, we can calculate the distance without using geometry by recreating the triangle on paper.
Try It!
Triangulation Example: How Far Away is that Tree?
Use graph paper and a protractor to complete the following example. You can use your own or print the PDF of graph paper and a protractor below.
Use graph paper and a protractor to complete the following example. You can use your own or print the PDF of graph paper and a protractor below.
In this example, we are trying to find out how far the tree is across the river from point A. Note the graph paper
scale used for this example: 4 cells = 100 metres. To do this, would walk to a point B on the riverbank and note the angle to the tree as measure from point A. Follow these steps:
That means the tree is 575 metres across the river from point A.
- The baseline produced on the riverbank is 450 metres, so we draw a triangle on the graph paper that has a baseline of 18 cells from point A to Point B.
- From point A, we draw a vertical line that is 90º from the baseline.
- We do not know how long to make this line yet, so extend it to the top of the page.
- Using a protractor, draw a line at the same angle as the one between the original baseline and the viewpoint B and the object. In this example, the angle was 52º. Draw a line until it meets the line extending from point A.
- You now have a scaled drawing of the triangle created on the riverbank.
- Measure the distance between point A and this new angle. In this example, it is 23 cells.
- Convert the measurement from cells to m. If 4 cells = 100 m, then 23 cells = 575 m.
That means the tree is 575 metres across the river from point A.
Parallax
Parallax is a very large triangulation measurement and can be used to estimate the distance between Earth and a distant star.
Have you ever looked over at the speedometer from the passenger's seat and wondered why the driver was driving slower than the speed limit? Maybe you have looked out the window of a moving car and watched as objects near the road sped by while larger objects in the distance seemed to move much slower?
You can experience parallax right now. Choose an object across the room from you. Close one eye and put your arm out in front, with your thumb up, covering the object. Keep your arm steady and wink with the other eye. You will notice that the object is no longer behind your thumb, but over to one side. Astronomers use parallax to determine the angles they should use when triangulating a star's distance from Earth.
Because the angles of a wide triangle are easier to measure than a narrow triangle, it is important to use a long baseline. In the example to the right (Figure 4), two observers on opposite sides of the Earth along the equator create a baseline the length of the diameter of the Earth.
If the observers at Point A and Point B take a picture of the appropriate region of the sky, the 'Object in space' will appear slightly shifted in the two images, but the objects in the background will appear not to have moved.
By using this shift to determine the angles between Point A, Point B, and the 'Object in space', astronomers can calculate the distant to the other objects in the distance.
Read pages 446 to 451 in your textbook Science in Action 9 to learn more about triangulation and parallax.
Parallax is a very large triangulation measurement and can be used to estimate the distance between Earth and a distant star.
Have you ever looked over at the speedometer from the passenger's seat and wondered why the driver was driving slower than the speed limit? Maybe you have looked out the window of a moving car and watched as objects near the road sped by while larger objects in the distance seemed to move much slower?
You can experience parallax right now. Choose an object across the room from you. Close one eye and put your arm out in front, with your thumb up, covering the object. Keep your arm steady and wink with the other eye. You will notice that the object is no longer behind your thumb, but over to one side. Astronomers use parallax to determine the angles they should use when triangulating a star's distance from Earth.
Because the angles of a wide triangle are easier to measure than a narrow triangle, it is important to use a long baseline. In the example to the right (Figure 4), two observers on opposite sides of the Earth along the equator create a baseline the length of the diameter of the Earth.
If the observers at Point A and Point B take a picture of the appropriate region of the sky, the 'Object in space' will appear slightly shifted in the two images, but the objects in the background will appear not to have moved.
By using this shift to determine the angles between Point A, Point B, and the 'Object in space', astronomers can calculate the distant to the other objects in the distance.
Read pages 446 to 451 in your textbook Science in Action 9 to learn more about triangulation and parallax.
Figure 4 – Two observers at points A and B on Earth have slightly different views of an object in space.
Watch
Another Triangulation Example
Watch the following video to understand triangulation and parallax better. As you watch, answer the following questions. How long will it take if you use the orbit of the Earth around the Sun as a baseline for triangulation? Objects that are closer to the observer appear to move more rapidly than objects that are further away – why does this occur?
Watch the following video to understand triangulation and parallax better. As you watch, answer the following questions. How long will it take if you use the orbit of the Earth around the Sun as a baseline for triangulation? Objects that are closer to the observer appear to move more rapidly than objects that are further away – why does this occur?
Spectroscope
Have you ever used a prism to create a rainbow on the wall? A spectroscope is like a prism for the light from a star. How does the spectroscope help scientists to identify the star’s composition?
A spectroscope separates the white light from a star in a very wide spectrum of colours. When the spectroscope separates the light, wide black lines appear in the spectrum. Scientists were puzzled at first by these black lines, but eventually they realized that particular elements in a star produced particular patterns of lines.
Now, scientists can use the spectroscope to discover which elements are present in a star.
Read pages 452 and 453 in your Science in Action 9 textbook to learn more about analyzing the components of a star using a spectroscope.
Have you ever used a prism to create a rainbow on the wall? A spectroscope is like a prism for the light from a star. How does the spectroscope help scientists to identify the star’s composition?
A spectroscope separates the white light from a star in a very wide spectrum of colours. When the spectroscope separates the light, wide black lines appear in the spectrum. Scientists were puzzled at first by these black lines, but eventually they realized that particular elements in a star produced particular patterns of lines.
Now, scientists can use the spectroscope to discover which elements are present in a star.
Read pages 452 and 453 in your Science in Action 9 textbook to learn more about analyzing the components of a star using a spectroscope.
Figure 5 – Using a spectroscope.
Watch
The Doppler Effect
Sound is not a form of electromagnetic energy. However, like electromagnetic energy, sound travels in waves. The waves of sounds can be stretched or compressed, and this has interesting effects on how we hear that sound. Watch the following video of a car speeding by blowing its horn. What do you notice about the sound?
Sound is not a form of electromagnetic energy. However, like electromagnetic energy, sound travels in waves. The waves of sounds can be stretched or compressed, and this has interesting effects on how we hear that sound. Watch the following video of a car speeding by blowing its horn. What do you notice about the sound?
In the video, the sound changes as it approaches the microphone and then as it moves away. This change is called
the Doppler Effect. As the car approaches you, the sound wave lengths are being compressed, which causes the pitch to increase. As the car moves away from you, the sound wave lengths begin to stretch out so the pitch begins to drop. If
you were inside the car, the car horn would sound the same the entire time.
The Doppler Effect and the Universe
Everything in the universe is in constant motion, but it can be very difficult to tell by looking through a telescope whether something is moving toward you, or away from you. Now sound cannot travel in space, so the Doppler effect as it applies to sound is of no use to astronomers. But the Doppler effect applies to light and other electromagnetic radiation as well. The change in frequency of light and other electromagnetic waves is very useful to astronomers, as they can use this effect to calculate how celestial objects are moving in relation to Earth.
To do this, astronomers record the light spectra of stars and galaxies. These light spectra can be either "stretched" or "squeezed" depending on whether or note the objects producing the light are moving away from or toward Earth.
Stars that are moving towards Earth have the dark lines of their light spectrum shifted more towards the blue end of the spectrum, and stars moving away from Earth will have a light spectrum that has shifted towards the red end of the spectrum. Stars that show no shift are moving in the same direction as Earth.
Everything in the universe is in constant motion, but it can be very difficult to tell by looking through a telescope whether something is moving toward you, or away from you. Now sound cannot travel in space, so the Doppler effect as it applies to sound is of no use to astronomers. But the Doppler effect applies to light and other electromagnetic radiation as well. The change in frequency of light and other electromagnetic waves is very useful to astronomers, as they can use this effect to calculate how celestial objects are moving in relation to Earth.
To do this, astronomers record the light spectra of stars and galaxies. These light spectra can be either "stretched" or "squeezed" depending on whether or note the objects producing the light are moving away from or toward Earth.
Stars that are moving towards Earth have the dark lines of their light spectrum shifted more towards the blue end of the spectrum, and stars moving away from Earth will have a light spectrum that has shifted towards the red end of the spectrum. Stars that show no shift are moving in the same direction as Earth.
Figure 6 – This diagram of the Doppler effect shows how waves are compressed in front of a moving object, and stretched behind it.
Watch
Red Shift – Blue Shift
Watch the following video to better understand how blue shift and red shift are used to determine how celestial objects are moving in relation to Earth.
Watch the following video to better understand how blue shift and red shift are used to determine how celestial objects are moving in relation to Earth.