Astronomy - PHYS1470

What are Kepler's three laws of planetary motion in order?

1. Planets move in elliptical orbits with the Sun as a focus

2. a planet covers the same area of space in the same amount of time no matter where it is in orbit, planet moves faster near Sun and slower further away, sweeping out equal areas in equal time

3. a planet's orbital period is proportional to the size of it's orbit

What is retrograde planetary motion?

Planets appear to move backwards, but this is not actually the case. Just occurs when a faster planet passes a slower moving one.

What are the heliocentric and geocentric models of the universe?

H: sun as the center G: earth as center, circles on circles on circles

As the Earth orbits the Sun, by how much does the closest star (Proxima Centauri - 2.6 x 10^5 AU from Sun) wobble in the sky?

diagram is the orbit of Earth around the Sun then a line from the Sun to the star, cross-section lines from opposite ends of Earth's orbit creating right angle triangle, use sohcahtoa (tan inverse) to find the angle in arcseconds

What is perihelion?

the point in the orbit of a planet, asteroid, or comet at which it is closest to the sun.

What is aphelion?

the point in the orbit of a planet, asteroid, or comet at which it is furthest from the sun.

What is eccentricity and its formula?

how much an ellipse deviates from a perfect circle, more squished is greater eccentricity, e = c/a where c is the distance from the center to focus and a is the semimajor axis

What is the formula derived from Kepler's third law?

P^2 = a^3 (P is period in years, a is semimajor axis in AU)

What is the equation for aphelion distance?

a(1+e) where a is semimajor axis and e is eccentricity

What is the equation for perihelion distance?

a(1-e) where a is semimajor axis and e is eccentricity

What is the conversion factor for degrees to arcseconds?

1* = 3600"

Draw a diagram of an elliptical orbit with a focus, a center, semimajor axis, etc.

*see image

Does this planet obey Kepler’s second law? If you were watching this planet during the entire orbit, would the speed be increasing, decreasing, or staying the same, how do you know?

It does obey 2nd law because it’s equal times equal areas. Speed would stay the same because it’s perfectly circular and doesn’t get closer to the center object.

What are Newton’s 3 laws?

1. An object moves at a constant velocity unless acted upon by a (net force), objects in motion stay in motion, objects at rest stay at rest

2. F=ma

3. For any force there is always an equal and opposite reaction force.

What is the Law of Conservation of Angular Momentum?

when objects interact, the amount of momentum gained by an object must equal the amount lost by the other object

What is Newton’s law of gravity?

F=GMM/r²

What are tides caused by?

change of gravitational force over distance

What are spring tides?

extra strong tides as a result of the Moon, Sun, and Earth in alignment, always happen when moon is full

What are neap tides?

extra low tide, moon’s orbit brings it perpendicular to the Sun, 1st and last quarter phases

What is tidal locking?

the moon spins once per month and also orbits Earth once per month, keeps the same face towards Earth at all times

What is tidal heating?

Earth’s rotation rate slowing down as tidal forces transfer rotational energy into heat

When does tidal destruction of stars happen?

tidal forces exceed the cohesive self-gravitational forces that hold the stars together

What is the formula to measure weight, or how much force on Earth?

F(g)=mg

What is the conversion factor for AU to meters?

1 AU = 1.496×10^11m

How do you convert degrees to radians?

1* = pi/180*

What is the relationship between Newtons and kilograms?

1N = 1kg m/s²

What is the formula for gravitational acceleration?

g = GM/r²

What is the gravitational constant?

6.67×10^-11 N m²kg^-2

What are simple definitions of mass and density?

mass is how much stuff makes up an object, density is how much mass is inside a given volume

Are photons affected by gravity?

despite having no mass, yes they are, the bend their direction of flight as they pass a massive object

What is flying?

flying is just falling and missing the ground (orbits and freefall explained)

What is the center of mass of an object?

the average position in an object of all its mass

What does tidal force depend on?

how strong gravity is from the 1st object, how wide the affected object is, how far the affected object is from the 1st object

What is the overall effect of tidal forces?

it stretches an object, for example the Earth is slightly football shaped as a result, water bulges up where the tidal force is strongest

Draw a diagram of tidal forces, showing high and low tide.

*see notes

How often do we have high and low tide?

each happens twice a day, high tide then low tide six hours later then high tide six hours later…

What is the Law of Conservation of Energy?

KE(1) + PE(1) = KE(2) + PE(2), the total energy of an isolated system is constant

A star is 250 million light years away. It appears to be 30 million years old when you look at it and it only lives for 120 million years before exploding. How long ago did the star explode?

160 million years ago

How many stars in the Milky Way?

100 billion (100000 million)

How big is the Milky Way?

100,000 light years across

What is the average distance between the Sun and the Earth?

1 AU, 8.3 light-minutes

What is the closest star to our solar system and how far away is it?

Proxima Centauri, 4.2 light years from Earth

Draw a diagram of the moon phases.

*see image

What is the formula relating distance, time, and velocity?

d=vt

What is the formula for area of a circle?

(pi)r²

What is the formula for the area of a sphere?

4(pi)r²

What is the formula for the volume of a sphere?

4/3(pi)r³

What is the formula for the circumference of a circle?

2(pi)r

What is the mathematical definition of acceleration?

change in velocity / change in time

What is the mathematical definition of velocity?

change in distance / change in time

Explain how a scale model works.

all sizes and distances are scaled down (multiplied) by the same factor

What is the scale factor of the solar system if the Sun is represented by a nerf ball (5.2cm)?

5.2/real diameter of Sun = 7.48×10^-11

Draw a diagram of the Earth’s orbit in relation to seasons.

*see image

When does summer happen?

when your hemisphere is most directly illuminated

Why do we have seasons?

1. More direct illumination delivers more heat to surface when tilted towards the Sun

2. Sun has a longer path to travel across sky in summer do more hours of daylight means more heating up

What is the difference between a solar day and a sidereal day?

sidereal day is the time it takes for stars to return to roughly the same place in the sky (23H56m), solar day is time for Sun to return to roughly the same place (24H)

Where on Earth is the Sun at Zenith at noon on June 21?

just at the 23.5* latitude (tropic of cancer)

What is the difference between a solar and a lunar eclipse?

solar is when moon’s shadow falls on Earth and the Sun is blocked, lunar is when Earth’s shadow falls on the moon

How big is the solar system?

0.00125 light years across

If the moon is in waning phases, how much of the total surface is illuminated?

exactly half

How old is the universe?

13.8 billion years old

Over what percentage of history of the universe did non-avian dinosaurs exist (240-66 myr)? figure it out mathematically

1.3%

How does light radiate?

in straight lines (but can bend around objects)

What is the equation for flux?

flux = power (lumosity) / area, F=L/A

What are wavelengths and frequency?

wavelengths are the distance between adjacent peaks, frequency is how often the peaks pass a given point in space

What is the equation for speed of light (c)?

c = (wavelength)(frequency)

What is the equation for the energy of a photon?

E = hf, h is constant 6.63×10^-24 kg m²/s

What is the speed of light?

300,000 km/s

What is an object’s spectrum?

quantifies how much light it emits at different wavelengths

What type of spectrum is produced when the light is emitted directly from a hot, dense object passes through a prism?

Continuous spectrum

What type of spectrum is produced when the light emitted directly from a hot, low density cloud of gas passes through a prism?

Emission spectrum

Describe in detail the source of light and the path the light must take to produce an absorption spectrum?

hot, dense energy source with a cool, low-density cloud between it and the prism

What happened to the light that is missing in the absorption line spectrum (represented by dark lines)?

absorbed by cloud

Which of these two absorption spectra was obtained from above Earth’s atmosphere and which was from the surface of the Earth (looking out)?

top one is from above Earth’s atmosphere, bottom one is from Earth’s surface (it includes the Sun’s lines and Earth’s atmosphere lines)

What is photon energy equal to?

the energy needed for electrons to jump from ground state, if it’s not equal it will pass through

What do the lines on absorption gradients relate to?

the lines on the Bohr model

What happens if an electron jumps down an orbital?

it loses energy that is carried out by photons

Explain the Doppler Shift.

change in wavelength of light as the source moves closer to observer or further away

What can the Doppler Shift be used to figure out?

how fast something is moving towards us

What is the difference between blue-shift and red-shift?

b: shorter wavelengths, moving towards subject, r: longer wavelengths, moving away from subject

Does blue-shifted light travel faster than red-shifted light?

no, all light moves at the same speed

Between gamma rays and radio waves, which is higher energy and which has shorter wavelengths?

gamma: short, high

radio: long, low

What is the tilt of the Earth?

23.5*

What is the difference between the equinox and the solstice?

equinox: sun is at celestial equator

solstice: sun is as far north (summer) or south (winter) as possible

Where on Earth receives 0h sunlight on December 21?

the north pole

Draw a diagram of the Sun’s place in the sky around the Earth, include solstices and equinoxes.

*see notebook

How do you find the position of the sun in the sky on summer and winter solstice?

summer: take the latitude of your location and subtract 23.5*, the result will be higher in the sky thus a smaller angle

winter: latitude + 23.5, lower in sky

What is lunar libration?

cumulative effects introduced by elliptical nature of moon’s orbit and it’s tilt relative to the orbit of the earth

Draw a diagram of the halo, bulge, and disk.

Sirius, the brightest star in the sky, is 9 light years distant. If you look at Sirius tonight, at what age will you be seeing it?

as it was 9 years ago

How many events listed in the table occurred by 75%?

3

What is the shape of Earth’s orbit around the sun?

very slight ellipse, almost perfect circle

Draw a diagram of the moon phases as seen from the northern hemisphere.

What does c refer to in Kepler’s first law?

the distance from the center to the focus

Draw a few diagrams to show different eccentric elliptical orbits.

The dwarf planet 2008 ST291 has a semimajor axis a=100 AU and eccentricity of e=0.57. What’s the farthest it gets from the Sun?

157 AU

Imagine you discover a new planet whose orbit around the Sun has a semi-major axis of 0.5 AU. What is it’s orbital period?

0.35

Define velocity.

the speed of an object AND its direction

Define acceleration.

a change in velocity through speed, direction, or both

How fast must WALL-E be moving to travel 100m in 5s?

20 m/s