Star Properties studied so far…• Period• Mass• Eccentricity• Red shift• Velocity• Temperature (Wiens Law)• Composition

– which elements and how much of each• Color• Age

A star with a continuous spectrum shines through a cool interstellar cloud composed primarily of hydrogen. The cloud is falling inward toward the star (and away from Earth). Which best describes the spectrum seen by an Earthbound observer?1) blue-shifted hydrogen emission lines

2) a red-shifted hydrogen continuum3) red-shifted hydrogen emission lines4) red-shifted hydrogen absorption lines

Velocity = distance / time

How do we measure the velocity of a star?

z = red shift =

How do we measure the velocity of a star?

l0

l

z = or

Velocity = c × z

How do we measure the velocity of a star?

What do you get if your l0 Ca line at 393.3 nm in the lab appears at 401.8 nm in the sky?

red shift = = 0.0216Velocity = cz

and the speed of light is 3 x 105 km/s So the star is receding at a speed of

V = (3 x 105 km/s) x 0.0216 = 6,480 km/s!

How do we measure the velocity of a star?

What do you get if your l0 Ca line in the lab at 393.3 nm appears at 786.6 nm in the sky?

red shift = ____Velocity = c x z,

and the speed of light is 3 x 105 km/s So the star is receding at a speed of:

V = (3 x 105 km/s) x __ = ______ km/s

How do we measure the velocity of a star?

What do you get if your l0 Ca line at 393.3 nm in the lab appears at 786.6 nm in the sky?

red shift = = 1Velocity = cz

and the speed of light is 3 x 105 km/s So the star is receding at a speed of

V = (3 x 105 km/s) x 1 = 300,000 km/s

How do we measure the velocity of a star?

We can measure velocityWe can measure distance

red shift = = 1Velocity = cz

and the speed of light is 3 x 105 km/s So the star is receding at a speed of

V = (3 x 105 km/s) x 1 = 300,000 km/s

How do we measure the age of the universe?

Star Properties studied so far…

• Period• Mass• Eccentricity• Red shift• Velocity• Distance• Temperature (Wiens Law)• Composition

– which elements and how much of each• Color

How do you measure the distance to a star?

Use 2 measurements of a star’s exact position in the sky, taken exactly 6 months apart.

Hubble found the relationship between a galaxy's velocity (the radial component, in a straight line) away from us (v) and its distance from us (d) approaches a fairly linear one, which is known as Hubble's Law:

v = H0 x dSo H0 is the slope of that line, which he found to be 73.3 km/s/Mpc

Or about 3.26 million light years

velocitycedis

timetan

yearsbillionyears

Mpckm

syear

kmsMpc

T

4.131034.1

11009.3

10156.31

731

10

19

70

So time = 1/H. Use this graph to tell us the age of the universe? Because we know that the slope of the line in the plot is 73 km/s/Mpc, we can simply write:

Life Cyclye of a Star

http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html

We can detect the velocity of a star through the Doppler effect by 1) measuring the shift in distance of the star. 2) taking photographs six months apart. 3) applying the inverse square law of brightness. 4) measuring the shift in wavelength of a spectral line.

The light from the east limb (edge) of the Sun is blue-shifted and the light from the west limb is red-shifted. This is because 1) different kinds of atoms emit light at the opposite edges. 2) the Sun is rotating. 3) the distance from the Sun to the Earth changes. 4) the two sides of the Sun are at different temperatures.

Most of the brightest stars in the sky are 1) relatively hot main-sequence stars that are relatively close to the Sun.

2) relatively cool main-sequence stars that are relatively far from the Sun. 3) relatively cool main-sequence stars that are relatively close to the Sun. 4) giant stars and relatively hot main sequence stars.