H-R Diagram (279.0K)
Manipulate the properties of a star (luminosity and temperature) and see how the star evolves along its evolutionary path at a rate determined by its nuclear burning timescale. As the star evolves, its color and size will change.

1		Sun's MS lifetime, according to your exercise with the time and mass sliders, is about: Need a Hint?
			A)	Ten million years.
			B)	One hundred million years.
			C)	Ten billion years.
			D)	One hundred billion years.

As the masses of stars were derived from studies of binary systems, it was soon found that mass played the most important role in predicting where the young star would begin its main sequence life.

2		As you used various masses with the sliders, what did you notice about the ZAMS (zero age main sequence) postion of the very young stars? Need a Hint?
			A)	The most massive ones are red giants, and the least massive ones are white dwarfs.
			B)	The red stars are the heaviest, and the blue ones the lightest.
			C)	The more massive the star, the longer it stays on the main sequence, since its fuel supply determines its longevity.
			D)	The more massive the star, the hotter and more luminous its ZAMS to the top left.

Stars exist over a fairly limited range of masses; if too massive, their great energy tears them apart into a cluster rather than a single body, and if too small, their gravity is not enough to ignite fusion, and they form brown dwarfs and not main sequence stars.

3		How does the one solar mass of our Sun compare to the range of main seqeunce masses? Need a Hint?
			A)	The Sun is more massive and luminous than almost all stars visible with the naked eye.
			B)	The Sun is about as low a mass as a star can be and still be a star.
			C)	The Sun lies almost in the middle of the known mass range, and thus about the middle of the main sequecne.
			D)	The Sun is not a main seqeunce blue star at all, but already a yellow giant.

Why is the main sequence main? There must be some common property that links the diversity of stars we find along the main sequence together into this continuum.

4		What do all main sequence stars have in common that explains the continuity of the main sequence from top left to lower right on the H-R diagram? Need a Hint?
			A)	They are all made of exactly the same elements.
			B)	The are all the same mass.
			C)	They are all single stars.
			D)	They are all still fusing hydrogen into helium for their energy.

We can use our examination of the H-R diagram to go beyond the simple main sequence hydrogen to helium stage, to more complex evolution into the giant phase when many different fusion reactions occuring all at once can cause the star to expand, pulsate, and even blow itself apart.

5		Based on this interactive, which of these best describes the future fate of our star? Need a Hint?
			A)	Will leave the main sequence soon, swell into a blue giant, then go supernova.
			B)	Should remain stable on the main squence for another five billion years, then evolve into a giant, shed its outer layers as a planetary nebula, and end up at bottom left as a white dwarf.
			C)	Will run out of hydrogen in about ten billion years, then collapse down to a brown dwarf.
			D)	The Sun will remain a g type main sequence star forever.