Astrophysics

Question 1

What is Kepler’s First Law?

Answer 1

Planets orbit the Sun in ellipses with the Sun at one focus.

Question 2

What is Kepler’s second law?

Answer 2

A line connecting a planet and the sun sweeps out equal areas in equal times.

Question 3

What is Kepler’s third law?

Answer 3

The square of the period is proportional to the cube of the radius.

Question 4

Explain Kepler’s second law.

Answer 4

K2 is conservation of angular momentum so as the radius increases the velocity must decrease to maintain a constant angular momentum.

Question 5

What is the virial theorem?

Answer 5

2KE + PE =0

Question 6

How is the virial theorem shown?

Answer 6

Equate the graviational and centripetal forces and simplify.

Question 7

How is the distance to a star measured using parallax?

Answer 7

Question 8

What is the apparent magnitude of a star?

Answer 8

The brightness a star appears from Earth.

Question 9

What is the absolute magnitude of a star?

Answer 9

The brightness a star appears from a distance of 10pc

Question 10

How do you calculate the apparent magnitude?

Answer 10

m=const-2.5logF

Question 11

How do you calculate the absolute magnitude of a star?

Answer 11

Question 12

What is the ideal gas law?

Answer 12

Question 13

How does radiation carry energy?

Answer 13

Photons carry energy between collisions with matter

Question 14

How does convection carry energy towards the surface of a star?

Answer 14

The bulk of gas causes currents

Question 15

How is the Virial Theorem applied to a star?

Answer 15

The kinetic energy is replaced with the interanl thermal energy U.

2U+PE = 0

Therefore the total energy

E=U+PE=U-2U = -U < 0

Therefore the star is gravitationally bound

Question 16

How is nuclear fissions triggered?

Answer 16

Typical decay mode for some nuclei triggered by absorption of a neutron.

Question 17

How are Newton’s and Kepler’s laws combined to get the Universal Theory of Gravitation?

Answer 17

Question 18

What formula relates absolute magnitude, apparent magnitude and dist

Question 19

What is Wien’s Law?

Answer 19

Question 20

What is the overall equation for nuclear fusion?

Answer 20

4 ¹H ►⁴He + energy

Question 21

Why does nuclear fusion release energy?

Answer 21

Helium is more tightly bound than hydrogen so the reaction yields energy.

Question 22

How it the relative strength of the fundamental force measured?

Answer 22

Its is the ratio between the potential energy and the rest mass energy

Question 23

What is the gravitaional coupling constant?

Answer 23

A dimensionless constant characterising the gravitational attraction between two elementary particles having non-zero mass.

Question 24

What is the fine structure constant?

Answer 24

A dimensionless constant characterising the strength of the EM interaction between elementary charged particles.

Question 25

What does the Grand Unification theory say?

Answer 25

The coupling strengths of the strong, electromagnetic, and weak force vary with energy (temperature) like this:

Question 26

What is the potential energy of an object at a large distance (assume infinite) from the Earth?

Answer 26

Assuming the distance is infinite the potential energy would be zero so as it move towards the Earth it gains kinetic energy and loses potential energy.

Question 27

What would the kinetic energy of an asteroid colliding with the earth be?

Answer 27

Equal to the change in gravitational potential energy from inifinity to the Earth's surface.

Question 28

What is evidence for a mass extinction caused by an asteroid

Answer 28

Enhanced iridium content of the soil layer indicating the end of the dinosaur period.

Question 29

How could a magnetic field reversal be a catastrophe?

Answer 29

The weaker field during reversal could cause more UV radiation to be incident with the Earth's surface. The ozone layer could also be depleted by cosmic rays that aren't blocked by the Earth's magnetic field

Question 30

What is the Solar constant?

Answer 30

The energy received from the sun per unit area per unit time at the distance of the Earth. S=1367W/m2

Question 31

What is the albedo of an object?

Answer 31

The albedo of an object is the fraction of incoming radiation that is reflected. e.g. White = 1 Black = 0

Question 32

What is the Stefan - Boltzman law

Answer 32

Question 33

How can the solar constant be derived from the Stefan - Boltzman law?

Answer 33

Question 34

Why is the sky blue?

Answer 34

The sky is blue due to Raleigh scattering of sunlight. This scattering is inversely proportional to the fourth power of the wavelength so because blue light has a lower wavelength than red light it is scattered much more so the sky appears blue.