Lecture 8

Question 1

what is the laser guide star used for?

Answer 1

by telescopes, to determine effect of atmospheric turbulence

it corrects stellar images

Question 2

what is VLA an example of?

Answer 2

using interferometry of using multiple smaller individual telescopes to achieve higher angular resolution

Question 3

what is adaptive optics?

Answer 3

helps to overcome atmospheric distortions

done by calculating the distortion caused by the atmosphere

Question 4

the sun and stars produce light via ______

Answer 4

nuclear rxns by nucelar fusion

Question 5

where do nuclear rxns occur in the sun?

Answer 5

the solar core

Question 6

how does the E from the solar core leave?

Answer 6

it is sent out via convection

Question 7

what are 3 types of nuclear rxns?

what is the main law behind these?

Answer 7

1) fission
2) fusion
3) decay

based on the fact that mass is always conserved

Question 8

describe fission.

what is the net reaction?

Answer 8

?an unstable parent nucleus (M) becomes two stable daughter nuclei (m,m)

energy is released

M = m+m+E

Question 9

which is more efficient for producing?

nuclear or chemical rxns?

what’s the problem with this?

Answer 9

nuclear

however, fission leaves unstable radioactive nuclei

Question 10

how does the sun produce energy?

Answer 10

nuclear fusion

Question 11

describe nuclear fusion

what are pros and cons?

Answer 11

m + m = M + E

E is released

pros

• efficient and clean way to produce E
• no radiactive byproducts

cons: hard to get fusion started

Question 12

____ nuclei prefer to be fused

____ nuclei prefer to be separated

Answer 12

light

heavy

Question 13

what is the only truly stable nucleus?

why?

Answer 13

iron

b/c it has the lowest binding energy

thus, heavier and lighter nuclei are less bound

Question 14

why is it hard for fusion to start?

how does the sun overcome this?

Answer 14

like charges repel

nuclei need to be pushed together before they fuse (needs lots of E)

the sun has very high pressure and density at the core, which allows fusion to happen easily

Question 15

____ is fused to ____ in the sun

Answer 15

H to He

Question 16

what is the pp chain?

Answer 16

the sun’s set of nuclear reactions

starts w/ two unbound H nuclei (p+p)

1) fuse to produce deuterium –> bound p+n –> produces neutrino and positron
2) deuterium hits a proton –> forms He 3 (p+p+n)
3) two He 3 collide –> forms He 4 (p+p+n+n+ and 2 protons

Question 17

name the zones of the sun from outward to inward

Answer 17

photosphere
convection zone
radiative zone
core