7/14/10: Course Project - Work in Progress

COURSE PROJECT - Work in Progress...thanks for your patience...

(Last updated/revised/ on July 27, 2010)



(Thanks to Rita S. S. for this very informative professional development course on using social media to enhance our classroom teaching and our own learning. We are benefiting from the countless hours you have dedicated in developing your course's excellent Wiki. Also, thanks to my classmates... all of you helped make this summer course an enjoyable learning experience!)



Introduction: For my project, I wanted to develop a blog with which I could make use of several of the tools and apps introduced via our class's Wiki (combined with the use of ordinary text entries) to discuss, explain, and illustrate a selected topic in introductory astronomy. I can then use the blog to easily save and share with students images and videos on topics related to our class discussions. As a new user of these tools and apps, I won't be surprised if you find the lesson developed below somewhat basic in its use of these technologies...


Topic of Proposed Astronomy Lesson: Short overview of the nature of meteoroids, meteors, and meteorites - In the sky, especially at night, what exactly are those sudden, brilliant multi-colored flashes of light we call "shooting stars"?

Since the time the first early-human looked up at the sky in wonder, our species has pondered the true nature of these suddenly appearing, short-lived bright flashes of light in the sky. Today, these are more familiar to us as falling stars or shooting stars. In astronomy, we refer to these bluish-green colored flashes of light as meteors. To understand the nature of these elusive objects, let's begin with...from NasaImages...

Next, some terminology we need to understand...

Asteroids:

"Potato-like" shaped planetisimal matter left over from the formation of the solar syatem that was not acrreted to a planet or moon, for example. These objects are found in orbits between the planets Mars and Jupiter. They range in size from the largest (Ceres at ~600 miles across) to the smallest (about the size of a compact car or desk). Perhaps about 150 asteroids of the 100,000 that are large enough to be photogarphed are 60 to 180 miles across. S-type asteroids are bright red, metallic nickel-iron that easily reflect radar waves, while the bright non-red asteroids are the pure nickel-iron M-type . The darkest (least reflective) asteroids are labeled C-type or carbonaceous and consist of a metal content similar to that found in the Sun. When asteroids collide, the impact debris can be scattered widely, some of which can eventually reach the Earth's orbit area.


Meteoroids:

A piece of interplanetary debris smaller than an asteroid. Typically, fall in the diameter size range between that of a dime and that of a quarter.


Meteorites:

Types and physical make-up: 1) Iron meteorites (or irons) - 80 to 90% iron with, traces of nickel, 2) Stony meteorites (or stones) - rocky (contain silicates), but can contain flakes of iron and/or nickel, and 3) Stony irons - about 50% iron and 50% rock.

Meteors:

About 25 million meteors a day are bright enough to be seen by the eye without using a telescope - perhaps many billions would be visible using a telescope. An estimated 1000 tons a day of them strike the Earth.

For illustration purposes...


A) From GoogleSquared: What typical meteorites look like... (Please note: I was unable to imbed this item, which would have shown a variety of meteorites)


http://www.google.com/squared/search?q=meteorite+types#table/agGxUSi_9y8ShDdvDqphCTdg


B) From YouTube: Sample videos of meteors and fireballs (very bright meteors)...

Chances of "impacts" - the risks are generally low, but meteorite impacts, large or small, are a reality in our solar system. The U.S. government does have a program to monitor the about 500 near-Earth orbiting Apollo asteroids - only 70 of these pose a risk to earth, because they are 1 km or larger and their eccentric orbits can bring them within about 0.05 A.U. of the Earth, where 1 A.U. is 93 million miles. In 1996, an asteroid passed the Earth harmlessly at about the distance from us to the Moon, which is only about 250,000 miles!


==> 120 large meteorite craters known on Earth so far...many of these are weathered (or on the seafloor) and are less impressive visually than Meteor Crater in Arizona;

==> Meteor Crater in Arizona: About 45 meters in size and 300, 000, 000 kg

==> Estimated: An impacting meteorite larger than 1 km across should statistically strike the Earth about once every 3 to 4 million years - large impactors of the K-T variety that drove the dinosaurs into extinction, say 10 km in size, might strike the Earth every 10 million years

==> Estimated: A 1 km sized meteorite would produce a crater 10 km wide due to the release of impact energy equivalent to about a 5,000-megaton atomic bomb, where 1-megaton is about 40X the size of the Hiroshima bomb of 1945. Energy released to form Meteor Crater was about that of a 25-megaton atomic bomb.


From NasaImages...the Chicxulub impact zone (K-T event) found in the Yucatan peninsula of Mexico west of Cancun near Merida...the impact occurred about 65 mya...