Midterm 1

Question 1

Eratosthenes and the size of the earth

Answer 1

Parallel rays from the sun hit a stick at alexandria, go directly into well at Syene. Measure angle of shadow from stick, then you know the angular difference between the stick and well. Measure the distance. Earth is 360 degrees. Solve for circumference.

Question 2

Precession of Earth’s axis

Answer 2

Rotation around the axis of rotation like a gyroscope

Question 3

Parallax

Answer 3

the distance dependent angular change in position from two different observation points.

Question 4

Retrograde Motion

Answer 4

When one planet over takes another causing the path of the planet to appear to go in reverse for a short period

Question 5

Keplers 1st Law

Answer 5

Sun at one focus of elipse

Question 6

Keplers 2nd law

Answer 6

Equal sweeps of area in equal time - when closer yo move faster. Farther you move slower

Question 7

Keplers 3rd law

Answer 7

Relative speeds from Radii

Question 8

aberration

Answer 8

Like the affect of rain - stellar position is offset in the direction of earth’s motion, independent of star’s distance.

Question 9

aberration vs parallax

Answer 9

Different direction and size. Aberration opposite earths motion, parallax opposite earth’s position.

Question 10

ecliptic

Answer 10

plane of earths orbit, titlted 23 degrees to celestial equator (seasons)

Question 11

Twinkling of stars

Answer 11

air bends star - varies with time causing twinkling due to wigling of single ray of light.

Question 12

why does the sun look yellow

Answer 12

it emits more yellow then b/r light

Question 13

continuous spectrum

Answer 13

continuous color spectrum, no black lines or breaks

Question 14

black body radiation

Answer 14

temperature decides spectrum, not shape or composition.

Question 15

reflected vs emitted light

Answer 15

reflected is visible light that we see based on what color light is absorbed and reflected from sun. Emitted light is energy released in form of light from temperature/heat. It is infared

Question 16

What can we estimate by looking at stars alone

Answer 16

brightness, surface temperature

Question 17

stars closer than us with the same apparent brightness - the closer one will…

Answer 17

have a lower luminosity

Question 18

what does a green line mean on a spectrum

Answer 18

it means green photons were absorbed

Question 19

What element can be ionized the most times

Answer 19

Fe

Question 20

Lots of H plus warm star

Answer 20

creates the strongest because excited to n=2 already. Hot stars weaker because its partially ionized. The more H the stronger the line.

Question 21

Why less Hydrogen in O-star

Answer 21

O star is too hot for neutral hydrogen

Question 22

heisenberg uncertainty

Answer 22

cant determine location and speed at same time

Question 23

supernova

Answer 23

star runs out of fuel left with inert iron core, which collapses with such force it explodes

Question 24

Chandrasekhar Limit

Answer 24

Some stars die gracefully due to degeneracy pressure, leave corpse. Otherwise supernova.

Question 25

Hans Bethe Fusion: Proton-Proton Chain

Answer 25

1. two protons fuse to form a deuterium (approx 10^9 years) and release a positron and a neutrino
2. single proton fuses with a deuterium resulting in ^3He (approx 1 second)
3. two ^3He fuse forming ^4He and two protons (approx 10^6 years)

Question 26

Degeneracy Pressure

Answer 26

Cannot compress electrons together extensively. Like jelly beans in a jar.