Tutorial for "Orion Nebula" Interactive

The Orion Nebula is one of the nearest locations in our
galaxy where stars are being formed now.  You can see it with
your own eyes: a faint, fuzzy patch of light just below
the belt in the constellation of Orion.  The visible portion
is just a tiny portion of the entire Orion Molecular Cloud 
complex, most of which is hidden from our view by thick 
layers of dust and gas.  You have seen several illustrations
of the Orion Nebula in this section, but it may help for you
to take a tour through a three-dimensional model of the visible
section of the Nebula.  This lab gives you several different
ways to investigate the region.

When you start the lab, you will see a picture frame with controls on 
the right.  At the bottom right is a toggle switch, which starts
in the "Explorer" position.  In this mode, you may look at a
portion of the Nebula from different points of view.  Begin with
the "Full View," which shows most of the visible portions of
the cloud.  Move the cursor into the picture, so that the cursor
turns into a small hand.  Then click and hold the left mouse button
while dragging the mouse.  The view will rotate, as if you were
flying around the cloud.  As you move, look carefully at the stars
scattered around you.  Do you see any which look fuzzy, or dirty?
What are they?

Clicking on the "Trapezium" button will give you a close-up look at
the four bright stars near the center of the Nebula (as shown by 
the red box in the thumbnail picture at upper right in the frame).  
Like all stars in the Nebula, these are very young, no more than a few million
years old.  All four members of the Trapezium are more massive than
our Sun.  The brightest of the four, called "theta Orionis C",
is the hottest, largest, and brightest of all.  It provides most of
the ultraviolet light which excites the gas in the Nebula, causing
it to glow.  The greenish color is produced by atoms of oxygen which
have had two of their eight electrons knocked away by ultraviolet
photons.

Clicking on the "Proplyd" button will show you a close-up view
of one the many proplyds (protoplanetary disks) in the Orion 
Nebula.  The location of this particular proplyd is shown
by the red box in the thumbnail picture at upper right in the frame.
Each proplyd contains a very young star, surrounded by
a disk of gas.  The star and disk together are surrounded by
a dense shell of material, a remnant of the cloud which collapsed
to form the star.  Notice how dense and dusty the disk is -- 
it blocks much of the light which passes freely through the 
cloud around it.  This proplyd is shaped like a teardrop, as 
are a number of others in the Nebula.  Something appears to be
pushing the gas on one side.  Can you figure out the source of
this "wind" in space?
 
If you move the toggle switch at lower right to "Guided Tour", 
you will see a movie showing the view as a spaceship flies through
the Orion Nebula.