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A Comet or a Star? |
Welcome to http://www.handsonuniverse.org/activities/Explorations/Comets/comet_or_star.html
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A Comet or a Star? |
A comet is different from a star..... Comets are like dirty snowballs and are part of our Solar System.
Comets belong to our Solar System. Orbiting the Sun are the planets and their moons, asteroids and comets. The orbits of comets are very elliptical. The Sun is at one focus of the ellipse. When the comet swings around near the Sun, the energy and charged particles from the Sun transform the comet. The dirty snowball comet becomes surrounded by a glowing coma of vaporized ices which become ionized gases and released particles. The solar wind pushes these gases and dust particles into tails which point away from the Sun.
Comets do not make their own light. (Although the energy of the Sun causes some of their gases to fluoresce.) We see comets because they reflect the Sun's light. The moon, asteroids, planets, even clouds in our sky are visible to us because they are reflecting sunlight.
Stars are very hot and they make their own light. Stars other than the Sun are very, very far away. Though stars are huge, they look like bright points of light because of their great distance from Earth.
Use the slice tool and Options for Axes Setup to display the light profile of a star as compared to a comet.
Compare Comet Hale-Bopp to a Star!
What do you notice about the symmetry of each slice?
Open Hands-On Universe Image Processing. Use Hands-On Universe image processing tools to compare a star to Comet Hale-Bopp. Open halebopp_apr97.fts; this image of Comet Hale-Bopp was taken at Yerkes by astronomer, Dave Rapchun. Open halebopp_sep96.fts; this image was taken by Dave Lane of the Burke-Gaffney Observatory. Look for a bright star in each image. Compare the star to the comet.
Slice across a star. Slice across the comet!
- Go to DATA TOOLS, select Slice.
- Click on the image with the mouse. Drag the mouse across a star. Click again to end your slice.
- Now slice across the comet. Try to get the coma of the comet and the tail in your slice.
- Slice windows appear that graph your slices. The X axis is the length of your slice in pixels. The Y axis is the brightness counts for each pixel along your slice.
- Use Options, Axes Setup to create graphs which have the same axes values. (For example, make the x axes to be a max of 1100 with tick marks at intervals of 200; make the y axes have a max value of 200 with tick marks at intervals of 50.)
Sketch a slice of a star. Sketch a slice of the comet. How are they different. How would you explain the differences?
What did you find out? How do the slices across the comet compare to slices across a star? Write down three of your observations.
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Do you think that these observations will always be true?
If not, what might be different and why?___________________________________________________
Download images: halebopp_apr97.fts and halebopp_sep96.fts.
