Week Four
Research in Space
Date: 1992
Grade(s): 4, 5, 6
Subject(s):
Research in Space:
During the first week, you made your own telescope. You can use it for your own personal exploration of space. Gallileo had only a simple telescope much like yours but he was able to make many discoveries. Astronomers today have much more complex and larger telescopes to explore space. Some have computers and cameras attached to aid in this study.
In addition to optical telescopes, radio telescopes are also used. These telescopes collect radio waves from objects in space. Visible light can not be used to study the center of our galaxy since dense gases block out the light. Radio waves aren't blocked by the dust so radio telescopes are used in this exploration.
A group of radio telescopes in New Mexico called the Very Large Array has been used. With this they have found that the center of our galaxy, the Milky Way, is a strong source of radio waves. This energy source is so strong and small that some astronomers think it might be a black hole. A black hole is a region in space in which such a large amount of mass is concentrated that no energy or light can escape. Astronomers believe that black holes may form after a large star collapses. The pull of the gravity would be so great that nothing could escape it.
The earth's atmosphere blocks other shorter waves which are given off from objects in space. Since these waves don't reach the earth they have to be studied from space. Today we have many orbiting satellites collecting data. In addition, the Hubble Space Telescope with a 2.4 meter mirror is in orbit. Even though you may have heard of several problems with this telescope much data has been collected. Keep in touch with the Skywatch Forum for some of these discoveries.
You can sometimes see a satellite in space. Look at the sky on a clear evening during twilight, a couple hours after sunset. Satellites look like a star moving slowly across the sky. Sometimes a satellite may move awhile and then disappear. You can see these satellites because the sun reflects off their metal surfaces. If you think you've seen a satellite, you might want to mention it in the Skywatcher's Forum.
Student Activity
(Adapted from Scott Foresman, Discover Science 5. 1991)
Computers on satellites in space send pictures to computers on Earth. This activity will help you explore the idea of making models by computer. The computer breaks down the pictures taken in space into a grid with tiny squares, each of which has a number. The computer transmits the list of all the numbers to another computer on Earth, which reconstructs the picture.
Materials:
Procedure:
Select a grid of squares on your paper with ten squares across and ten squares down. Think of a simple picture or design that could be drawn by lightly coloring squares in your grid. Each box should be either colored or left blank. A number or letter is easiest to make. Draw in your picture.
Write a 1 on all of the white boxes. Write a 0 on all of the colored squares. Now you can make a code for your picture in much the same way a computer makes one. On another sheet of paper, list the 1's and 0's. Start with the top row, left side and list all the numbers in that row. Then list along side the previous row's numbers all the numbers for each of the other rows in the same way.
Ask a friend to try drawing your picture from just the code you developed for it.
Question:
Besides giving us information about space and the universe in which we live, research in space has also had many practical uses for our lives. Satellites in space carry telephone and television signals around the world. The "satellite dish" you have seen in some peoples' yards serves as an antenna to pick up television signals directly from satellites in space. Satellite pictures from space are used to study resources such as plant life, mineral deposits, or weather patterns.
New technologies also result from the space program. For example, electronic devices need to be small and light weight to go into space. The silicon chip was developed for this reason, but it is now used in computers, calculators, and other everyday tools. Fabrics developed for the space program are now used in blankets, gloves, sports equipment, and insulation.
Distances are so large in space that traveling millions of miles is nothing. Distance is measured in light years. One light year is the distance light travels in one year. Light travels fast enough that it reaches the earth from the sun in about eight minutes. The light from Alpha Centauri, the next nearest star to the earth, takes about four years to reach the earth. This means that it is about four light years away.
To get an idea of distances just within our solar system imagine taking a Concorde jet to the sun. A Concorde flies about 1,000 miles per hour. The distance to the sun is 93,000,000 miles. How long would it take to reach the sun? Can you figure it out? Now just think how much longer it would take to get to Alpha Centauri or another star beyond the solar system.
Since scientists have not yet been able to travel to all these places and only a few unmanned space probes have ventured into outer space, ways of measuring distances need to be figured out from Earth. One way is the parallax method. Parallax is the difference in the direction of an object you see from two different points. For example, hold a finger up in the air in front of you. Close one eye and notice where you see your finger is in relation to the wall. Now close the other eye and notice the part of the wall that the same finger is now covering. Your eyes are in two different places on your head so each sees things from a slightly different angle. This is known as parallax.
Astronomers use this idea to measure distances to the stars. To find the distance a photograph is taken of the star's position in the sky. A few months later, when the earth is in a different position another photo is taken. These two views are used to figure out the distance to the star. Better means will need to be found for the very distant stars as the parallax is too small to measure.
Class Activity: (Adapted from Scott Foresman, Earth Science. 1990.)
You will need to work in groups of two or more. The purpose of this activity is to make a physical model of a system for determining how parallax can be used to determine distances in space. This activity uses the metric system since science uses that system of measurement .
Materials:
Procedure:
Place two cups on the table about 30 cm apart. Make six marks on the chalkboard or paper about 50 cm apart. Number these marks 1 through 6. This paper or board should be on the wall near the table.
One group member should position himself or herself behind the table with his or her eyes level to the cups across from the chalkboard or paper. If you have enough room move back from the table about 1 meter.
Draw a picture of the cups as they appear. Also include the positions and numbers of the chalk marks in relationship to those cup positions. Now move 1 m to the left. Another team group member could move to this position if he or she is able to keep his or her eyes at the same height as her or his partner's. Draw the paper cups and marks as they appear now. Keep your eyes at the same level as you move. Now move 1 m to the right of your original spot and draw your observations again. Move to another spot of your choosing and again draw your observations.
Questions:
(Note to teachers: The stars are so far from earth that the two pictures from different spots on earth would show no change in their apparent position.)
Optional Activity: Making a Model of Star Distances (Adapted from Scott Foresman, Discover Science 5.1990)
Teacher's Note: This is an optional activity that may be used in addition to or in place of the class activity on parallax. To involve the whole class you may want to have several groups working at once. At least four students are needed in each group.
Materials:
Procedure:
Use the top of the jar as a pattern to trace three circles on each of the three colored sheets of paper. Cut these out and tape to the ends of the three meter sticks. Place these circles so the end just touches the 1 cm line.
Three students should hold the sticks in a straight line. The student with the yellow circle should be all the way across the room from you. The person with the red circle should be halfway across and the person with the blue circle should be about a meter away from the viewer.
The viewer should sit down and close his or her right eye, moving his or her face until the blue circle appears to cover the red and yellow circles. The viewer should hold the centimeter ruler in their right hand with the "1" just appearing to touch the right side of the blue circle.
The student viewing should then open their right eye and close their left. Record the number of centimeters between the circles. This should be tried with several viewers.
Questions:
Stars
Another area of research for astronomers is the star's brightness or magnitude. The star's magnitude depends on the star's distance from earth, its size, and the amount of light it gives. To visualize how distance affects magnitude, imagine being outside on a very dark night. Several blocks away is a headlight from a motorcycle. Close to you is a flashlight. If all you could see was the light, you wouldn't know that the light in the distance was actually as bright as it is. It wouldn't be until that light started to move toward you that you would see that it was much brighter than the flashlight.
If you think of it the other way, the flashlight would become very dim in comparison to the motorcycle headlight blocks away, if the person holding it started to back away from you. In the same way a star's distance from Earth affects how bright it appears.
A star's temperature also affects how much light it gives and the color it appears. The burners on a stove are black at first but as the heat is turned higher they turn red. If it could be turned high enough they would change to yellow and then blue-white. If something is white hot it is hotter than something red hot.
Size is also a consideration in the brightness. The larger of two stars of the same color will be brighter than the smaller one. Astronomers give number values to the magnitude to help them compare the magnitude of different stars. The brightest star is given a -1.4 value and the faintest object that can be seen with only large telescopes a +24.5 value. A photometer is used to measure the brightness of stars by attaching it to a telescope. Light enters and produces an electric current. The strength of the current is used to determine the brightness.
Enrichment
Another way astronomers try to determine distances in space is by using cepheid variables. These are stars whose brightness vary on a regular basis. One such star is the North Star or Polaris. It brightens and dims every four days.
During the early part of the Twentieth Century, it was discovered that the timing of the cepheids' variations were related to their brightness. Since the stars examined were all in the same nearby galaxy and at roughly the same distances the timing of their variations could be related to their brightness. This means that astronomers could determine the distances of Cepheids by timing their variations and comparing the actual brightness of the stars with the their brightness seen from Earth.
One problem is that dust in our galaxy and other galaxies absorbs blue light which makes the Cepheids appear fainter and farther away than other Cepheids of the same distance not seen through the dust. Today this problem is being solved by examining the Cepheids with detectors sensitive to red and infrared light. Both of these kinds of light aren't hindered by dust so estimates of distance have gotten much more accurate.
By finding Cepheid variables in other galaxies we can begin to figure out the distances of these galaxies. Photographs are taken and studied for changes in brightness. The process often takes longer than desired because the observations and photos can only be taken on clear nights.
Student Activity ( For the distance experts.)
Materials:
Procedure:
Suppose you had discovered a new Cepheid that brightened and dimmed every 10 days (period) and its magnitude was on the average 16.5. Using math and tables astronomers have prepared, you can find the distance. Look at the tables in diagram 23 of the teacher's packet. The table on the top shows the period and magnitude. Use this to find the absolute or actual magnitude for a star. (The absolute magnitude is the brightness a star would have compared to other stars if they were the same distance from the earth.) By subtracting the average magnitude we see, with the absolute magnitude, we have of way of comparing the two. This is called the distance modulus.
Average magnitude - Absolute magnitude = Distance modulus.
Use this number in the second table to find the distance.
Now try some problems for yourself. You and a partner may want to try finding the distances for stars of different magnitude. Make up some problems to see if you have figured out how the tables work.
Assignment:
Add the words, radio telescope, black hole, Milky Way Galaxy, light year, parallax, magnitude, cepheid variables, and North Star to your Student Astronomy Workbook.