| Who_is_Who_in_Atomic_and_Plasma_Physics_(WWAPP) Database from Plasma Laboratory at Weizmann Institute of Science, Israel. |
| AP_Statistics_at_the_College_Board The College Board's official AP Statistics page. Course description, sample exam questions, teacher resources and contact information. |
| Business_Statistics Covers averages, normal distribution, best curve fit and skewness. Includes resource links. |
| Center_for_Statistics_Education The American Statistical Association sponsors educational resources for K-12 and above. ASA's LearnStat program provides continuing education for professional statisticians and educators. |
| Computer-Assisted_Statistics_Teaching_(CAST) A complete web-based course in introductory statistics. Registration required. |
| Curve_Fit Beginner's guide to nonlinear regression. Emphasizes how to interpret results. |
| The_Data_and_Story_Library Online library of datafiles and stories that illustrate the use of basic statistics methods. The goal is to provide data from a wide variety of topics so that statistics teachers can find interesting, |
| DISCUS Discovering Important Statistical Concepts Using Spreadsheets. Uses Excel spreadsheets to investigate statistical concepts. |
| Intro_Stat__EPR_Approach This site contains information about the Entity-Property-Relationship (EPR) approach to the introductory statistics course by Donald Macnaughton. |
| Introduction_to_Mathematical_Statistics Lecture notes from a year-long course in mathematical statistics. |
| Introductory_Statistics___Concepts,_Models,_and_Applications_by_David_Stockburger An online, searchable introductory statistics text. By David Stockburger of Southwest Missouri State University. |
| Intuitive_Biostatistics Harvey Motulsky, OUP (1995). Site for the book, with online extracts (PDF). |
| K-12_Statistics_Education Resources in statistics including lessons and useful data sets. |
| Number_Watch Monitors the media in search of misleading numbers in news, politics and science. |
| Numeracy_in_the_News Features sections on data collection and sampling, creating graphs, probability and inference. Also, includes special topic articles and teacher spreadsheet programs. |
| Primer_in_Statistics Covers mean, mode, median, standard deviation, area approximation, charts and testing for normality. |
| Resources_in_Statistics,_Quantitative_Methods_and_Experimental_Design Statistics-related exercises and humour, for courses from high school to graduate level. |
| Rice_Virtual_Lab_in_Statistics This resource for teaching statistics includes java simulations, case studies, an online text, and an analysis lab. |
| SAS_JMP Tutorials for SAS's JMP Statistical Analysis Software. |
| Seeing_Statistics Tutorial using graphs to illustrate concepts. Includes glossary of terms. Online purchase. |
| StatiBot An on-line expert system for finding statistical tests appropriate to a dataset. |
| Statistica Book, with worked examples and courses are specially designed for the non-mathematicians. Includes excerpts and ordering information. |
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| Statistical_Home_Page_(David_Howell) This site contains a variety of pages related to the teaching of parametric and nonparametric statistics. It includes examples, content, lecture notes, and ideas on teaching. |
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| Statistics_Education Links related to statistics education: online teaching material, courses , handouts, exercises, articles, datasets, and other useful links. Collected by Juha Puranen from the Department of Statistics |
| Statistics_In_A_Day A short course in data analysis. A 70 page book designed for a one-day workshop/course in data analysis. A number of versions are available, suitable for different groups of people. Ideas explained i |
| StatNotes__Online_Textbook_in_Statistics Graduate-level text by David Garson of North Carolina State University. Especially well suited for social sciences. |
| STEPS__STatisical_Education_through_Problem_Solving A program for teaching statistics through problem so students will recognize its applications. Free CBL software with modules in pyschology, biology, geography and business. Glossary of statistical te |
| SurfStat_australia Online, introductory statistics course notes. Includes an extensive glossary, interactive exercises, javascript probability tables and some java applet animations. |
| Teach/Me_-_Data_Analysis HTML-based textbook with integrated statistical package and embedded interactive examples allowing the user to experiment with various models and methods. On-line purchase. |
| NYTimes_com_-_The_Odds_of_That Long article discussing examples of happenings which appear at first glance to be related, but are not. [Requires free nytimes.com registration to view.] (August 11, 2002) |
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Space
Science News home
Sept. 7, 1999: As photographed
from space, the Earth looks like it is floating in a black void.
But, unseen by our eyes and most cameras, the Earth is actually
surrounded by a complex system of interacting electric and magnetic
fields, electric currents and charged particles called the magnetosphere.
Right: If a camera didn't compensate for the bright
sunlight in space, stars would be seen in the background and
the Earth would appear as a bright white orb. Because distant
stars aren't as bright as the Earth, a low photo exposure results
in a black background.
The magnetosphere provides a barrier between our planet and particles
continually given off by the Sun's corona called the "solar
wind." These particles constitute a plasma - a mixture of
electrons (negatively charged) and ions (atoms that have lost
electrons, resulting in a positive electric charge).
Recent Headlines
December 3: Mars Polar Lander nears touchdown
December 2: What next, Leonids?
The
plasma of the magnetosphere has many different levels of temperature
and concentration. The coldest magnetospheric plasma is most
often found in the plasmasphere, a donut-shaped region surrounding
the Earth's middle. But plasma from the plasmasphere can be detected
throughout the magnetosphere because it gets blown around by
electric and magnetic forces.
Left: Artist's concept of the magnetosphere. The rounded,
bullet-like shape represents the bow shock as the magnetosphere
confronts solar winds. The area represented in gray, between
the magnetosphere and the bow shock, is called the magnetopause.
The Earth's magnetosphere extends about 10 Earth radii toward
the Sun and perhaps similar distances outward on the flanks The
magnetotail is thought to extend as far as 1,000 Earth radii
away from the Sun.
Gallagher has developed a general model to describe the density
of the plasma surrounding the Earth. His paper, "Global
Core Plasma Model," will be published in the Journal
of Geophysical Research. "Core plasma" refers to
the low-energy plasma (zero to 100 electron volts) that makes
up the plasmasphere.
The plasmasphere extends out to as little as 2 to 3 Earth radii
and, under quiet conditions on the 
evening
side, perhaps more than 6 Earth radii. (Because conditions in
space constantly vary and regions never have exact boundaries,
plasma physicists measure the plasmasphere relative to the size
of Earth: 4,000 miles [6,400 km] is about one Earth radius.)
The extent of the plasmasphere depends on space weather activity.
High levels of activity erode the plasmasphere; long periods
of quiet allow the plasmasphere to expand.
Right: Click
the image for a 3D simulation of the magnetosphere's shape.
The Sun is off screen to the left. The animation begins showing
the Earth, which recedes as the shape and size of the magnetosphere
comes into view. The solar wind deforms the magnetosphere into
its characteristic shape. Where the magnetosphere and the solar
wind meet is the "bow shock," represented in the animation
by a faint, translucent bullet shape. Credit: Digital
Radiance
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Rockets, satellites and the space shuttle have flown
in parts of the core plasma neighborhood. By taking various measurements
of this region, scientists have gradually come to understand
the basic nature of the entire plasmasphere.
"We've been flying in plasma for over 40 years and have
slowly gained a statistical picture of what things are like,
such as the density and proportion of oxygen, hydrogen, and helium,"
says Gallagher.
But our understanding of the plasmasphere
is not complete. For one thing, all the various measurements
have resulted in many independent models of specific plasma regions.
By combining previous work, Gallagher's model attempts to describe,
mathematically, a general, complete image of the plasmasphere.
Left: Animation of the Earth's plasmasphere as it would
appear in extreme ultraviolet light (30.4 nm wavelength). This
simulates the view from the IMAGE satellite due to launch in
February 2000. To watch a QuickTime movie of this animation,
click here (6.5MB file).
"This model begins to paint a picture, but it's something
of a Frankenstein's monster," says Gallagher, referring
to how his model is pieced together from several different, dissimilar
models. "A significant issue is how you smooth the stitches."
Gallagher's model combines the International Reference Ionosphere
(IRI) model for low altitudes with higher altitude models. The
part of our atmosphere that contains plasma - the ionosphere
- is generally 90 to 1,000 km (54-620 mi.) above the ground.
Web Links
Space
Plasma Physics - research on plasma at NASA's Marshall Space
Flight Center.
Earth's
Solar Environment - International Space Physics Educational
Consortium.
Exploration
of the Earth's Magnetosphere - overview of NASA research
on the Earth's environment in space.
The shorter wavelengths of sunlight, ranging from the
ultraviolet to X-rays, ionize the Earth's upper atmosphere by
tearing electrons off atoms. The ions and electrons do not readily
recombine in the ionosphere because particle collisions are infrequent
in the rarified atmosphere. Ionospheric densities range from
a peak of about 1 million particles/cm3 down to
many thousands of particles/cm3. The densities
continue to fall as you move to higher altitudes.
From the equator to the middle latitudes of Earth, the ionosphere
joins smoothly with the plasmasphere. Beyond the outer boundary
of the plasmasphere, the densities of plasma in the magnetosphere
can fall as low as 0.01 particles/cm3.
"The plasma environment around the Earth is a natural
extension of Earth's atmosphere, ionized by the Sun," says
Gallagher. "Any planet that has an atmosphere is going to
have energy from the Sun imparted to the atoms. The consequences
are that lighter elements escape. But Earth's magnetic field
traps much of this escaping gas. A planet like Mars that has,
at best, a weak magnetic field, also has a very thin atmosphere.
Some researchers have speculated that the Earth's magnetic field
may pla
y a role in slowing the loss of our atmosphere into
space."
Right: Artist's concept of the interaction between the
magnetosphere and the Sun. The Earth's magnetic field provides
a barrier to the solar wind.
Our atmosphere provides
pressure, proper temperature, and oxygen - fundamental requirements
for life on Earth. Without the atmosphere, one side of our planet
would freeze while the other would broil under intense solar
radiation.
Gallagher's model may contribute to our understanding of how
the Earth's plasma affects our quality of life. Radio waves and
power lines are affected by the presence of plasma, as are satellites
and the Space Shuttle. Plasma can cause an electric charge to
accumulate on one part of a spacecraft but not another, sometimes
resulting in an electric arc, or discharge. These electric arcs
can disrupt or destroy sensitive electronic components.
Gallagher will be able to refine his model with data from
the IMAGE satellite, due to launch in February 2000. IMAGE will
give us a better picture of the Earth's magnetosphere, and because
plasma is bound to magnetic fields, IMAGE should also improve
our understanding of how the plasmasphere and the magnetosphere
interact.
More
web links
Space
Weather Camera Set for Launch in 2000 - Feb. 16, 1999
Imager for Magnetopause-to-Auroral
Global Exploration (IMAGE) - satellite facts and objectives.
Space Physics Textbook
- University of Oulu Space Research Group.
More Space Science Headlines
- NASA research on the web
NASA's Office of Space Science press releases and other news related to NASA and
astrophysics
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For more information, please contact:
Dr. John M. Horack
, Director of Science Communications
Author: Leslie
Mullen
Curator: Linda Porter
NASA Official: M.
Frank Rose
