EARTH-MOON DISTANCE - IMAGE & REALITY

Image Processing Activity

In this activity you will measure the distance between Earth and Moon in an image; model the scale distance between Earth and Moon using a globe or other sphere. (Confronting misconceptions; a common misconception; converting image file formats.)


Look at the image below and the apparent distance between Earth and Moon. How does this fit with your previous ideas?

Use the diameter of Earth as 1 unit. How many Earth diameters are between Earth and Moon in the image?

The image you see below is linked to a larger image that you will use for the image processing assignment. Click on the image to go to the larger image, which you will need to download.

 

Image Source: http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA00559

Image credit: NASA/Jet Propulsion Laboratory/Arizona State University

Original Caption Released with Image:

2001 Mars Odyssey's Thermal Emission Imaging System (THEMIS) took this portrait of the Earth and its companion Moon, using the infrared camera, one of two cameras in the instrument. It was taken at a distance of 3,563,735 kilometer s (more than 2 million miles) on April 19, 2001 as the 2001 Mars Odyssey spacecraft left the Earth. From this distance and perspective the camera was able to acquire an image that directly shows the true distance from the Earth to the Moon. The Earth's diameter is about 12,750 km, and the distance from the Earth to the Moon is about 385,000 km, corresponding to 30 Earth diameters. The dark region seen on Earth in the infrared temperature image is the cold south pole, with a temperature of minus 50 degrees Celsius (minus 58 degrees Fahrenheit). The small bright region above it is warm Australia. This image was acquired using the 9.1 µm infrared filter, one of nine filters that the instrument will use to map the mineral composition and temperature of the martian surface. From this great distance, each picture element (pixel) in the image corresponds to a region 900 by 900 kilometers or greater in size or about size of the state of Texas. Once Odyssey reaches Mars orbit each infrared pixel will cover a region only 100 by 100 meters on the surface, about the size of a major league baseball field.

Part 1: Creating a Scale Model

 

Before beginning the technical aspect of this project, you will need to do a hands-on demonstration. During Module 2 you found circumference of the Earth at the Equator is just over 40,000 km. The average Earth-Moon distance is about 385,000 km, which is about 9.5 times the circumference. To make a quick scale model of this system, you will need a globe and a ball about a quarter of it's diameter to represent the Moon. Then,

You've just constructed a rough model of the Earth-Moon system with scaled size and distance.

Note: The actual Earth-Moon distance ranges from about 360,000 to 405, 000 kilometers, depending on the position in the Moon's orbit.

Part 2: Image Processing - Downloading & Converting Images

To complete this activity you will need to download the Earth-Moon Distance image. The above image is linked to a larger one, so take the link to the larger image, then download. You will notice that this image is in JPG format. Your image processing software requires all images to be in TIFF format. While some sites will let you download images as a TIFF, many of the images you will be downloading from the Internet will come in JPG or GIF format. You will need to convert these images from their original to a TIFF format. You can do this using image editing shareware. A good source of shareware for all computers is the Tucows site. Links to image editing software are:

TuCows Image Editors for Mac - Several options are available; I've had a great deal of success with Graphic Converter

TuCows Image Editors for PC - Several options are available; I've used Graphic Workshop successfully in the past

Shareware is software that allows you to use it free for a trial period. After the end of the trial period you are asked to pay a small shareware fee if you intend to keep the software.

Regardless of which software you choose, you will need to open up the Earth-Moon JPG image and convert it to a TIFF format. Because knowing how to convert images is an important tool in using image process, we ask that you learn how to do this step. Help each other out, but please do not convert the image for someone else. Knowing how to convert images will allow you to use this software for multiple purposes in your classrooms. Once you have downloaded and converted your image, following the instructions for the software you choose, you are ready to use the image processing software to make measurements.

Part 3: Image Processing - Making Measurements

When measuring, you may use either the upper or lower part of the image, it won't make a difference which one you choose. To complete this activity complete the following steps:


Submit to the Module 3 Homework Conference:


This activity written by Elizabeth Roettger & Donna Governor for "Comparative Planetology," Spring 2002

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