Students will:Learn about two major types of orbits for satellites.
Learn that Landsat-7 is a polar-orbiting satellite.
Use math skills to figure out how far Landsat-7 is from the Earth.
Materials:
Globe (the type that spins on a stand works best)
Flashlight
Landsat-7 poster (see Tips for Teachers)
Landsat orbit picture
Engagement
Hold a globe for the students to see. Ask them "How do you think Landsat-7 takes pictures of the Earth?" (You might want to remind them that Landsat-7 takes images of the entire Earth and show them a poster of Landsat-7.)
Exploration
Shine a flashlight on the globe and pretend it is Landsat-7. Ask a couple of students to show the class how they think Landsat-7 travels by moving the flashlight and/or by moving the globe (you might want to darken the classroom.)
Explanation
After the students have a chance to show the movement of Landsat-7, write down geo-stationary satellites and polar- orbiting satellites on the board. Explain each orbit to the students by demonstrating it with a globe and a flashlight (see Tips for Teachers). Explain to the students that Landsat-7 is a near polar-orbiting, sun-synchronous satellite at an altitude of 705 km above the Earth. Its orbital path is within 8 degrees of the North and South Poles. (Sun-synchronous is when a satellite takes picture of the same latitude at the same local time. The images have to be taken at the same time because scientists need to compare image data with constant lighting conditions for its specific sensors). Spin the globe and move the flashlight from pole to pole and tell the students the satellite will return to take the same images at the same time every 16 days.
Extension
Landsat-7 travels from the North Pole to the South Pole and back in 103 minutes (that is about 500 miles per hour - traveling from Washington, DC to Atlanta, GA without stopping!) Have the students calculate the circumference of the path that Landsat-7 travels and have them figure out how many Washington Monuments it takes to reach Landsat-7's orbit (see "Tips for Teachers") .
Evaluation
Ask the students why Landsat-7 is a near-polar sun-synchronous satellite rather than a geo-stationary satellite.
Answer: Landsat-7 is a near polar, sun-synchronous satellite because the satellite can travel from pole to pole to take images of the entire Earth. Also, consistency in data is very important. Landsat-7 takes images of the same location at the same local time. This allows scientists to compare data with constant lighting conditions. Polar-orbiting satellites also allows the satellite to take images of the Earth with better spatial resolution than a geo-stationary satellite, since the Landsat-7 satellite is closer to the earth (about 470 miles) than typical geosynchronous satellites (about 35,000 miles).
Tips for Teachers
Geo-stationary Satellite. A satellite that appears to be stationary with the Earth because it orbits around the Earth, in the same speed and in the same direction. At the high altitude (about 38,500 km), the satellite appears to be stationary or "parked" over a fixed point on the equator. (Shine the flashlight to a certain area and keep shining the same area as you spin the globe slowly.) A geo-stationary satellite takes pictures of one area of the Earth (normally about 1/4 of the Earth's surface area, and continuously throughout the day.
Polar-orbiting satellite. A satellite that orbits from the North Pole to the South Pole. (Start moving the flashlight from the North Pole to the South Pole and back up to the North Pole. Spin the globe very slowly and move the flashlight around the globe until the flashlight shines every spot of the globe from North to South.) Polar-orbiting satellites are generally lower in altitude (400 to 900 km, about 28,000 km lower than geo-stationary satellite) and can achieve better spatial resolution.
Calculating the circumference of the Landsat-7 orbit. Provide the following information and ask the students to calculate the circumference of the Landsat-7 orbit.
The distance between Landsat-7 and the surface of the Earth = 705 km
The radius of the earth (the earth's surface to the center of the earth) = 6371 km
Conversion factors: 1 mile = 5280 ft; 1 mile = 1.6 km
Circumference formula is: 2 (pi) (r) = 2 (3.14) (r)
Answer:
The circumference of Landsat-7's orbit is: 2 (pi) (r) = (2) (3.14) (705 + 6371 km)= 44,460 km
You can have the students convert km to miles after they solve for the circumference of Landsat-7.
Pose another question about the Landsat-7 orbit. How many Washington monuments would it take to reach Landsat-7 from the surface of the earth? Or use any other object that students can relate to.
Height of the Washington Monument = 555 ft
The distance between Landsat-7 and the surface of the Earth = 705 km (438 mi)
Answer:
1. Number of feet in 438 miles. (438 miles) (5,280 ft) = 2,312,640 ft
2. Number of Washington Monuments in 2,312,640 ft. (2,312,640 ft / 555 ft) = 4,167 Washington Monuments!
The educational standards met in this lesson can be found in the Standards section.
Pertinent Internet Sites:
NASA's site on learning about space: http://octopus.gma.org/surfing/satellites/inorbit.html
This web site is a great place to learn about how satellites work:
Satellite orbits
This site is useful to learn about satellite orbits, aimed for middle school students.
Books of interest:
A book introducing remote sensing and its applications for middle school students: Seeing Earth From Space by Patricia Lauber, Orchard Books, 1990.
An easy-to-read text with colorful pictures about satellites for upper elementary school students: Satellites by David Jefferis, Franklin Watts Ltd., 1987.A lithograph that describes various satellites that were launched in the 1990s; available from NASA GSFC Education Resource Centers: Goddard Space Flight Center Missions of the 1990s and Beyond NASA Lithograph HQL-347.
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