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Astronomy > Lectures 1-6 > Flashcards

Lectures 1-6 Flashcards

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1
Q

How many planets are there?

A

8

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2
Q

How many moons are there?

A

172 (disocvering one a year approx.)

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3
Q

Describe the Milky way. Type of galaxy no of stars etc.

A

-spiral galaxy, 100 billion stars orbitting a supermassive black hole, we are at the outer edge

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4
Q

What is a local group of galaxies?

A

-around 50 galaxies, held together by gravity, in ours= only 3 that are big -Milky Way
- Andromeda (M31)
-M32
most of the galaxies= dwarf- satellites of bigger galaxies

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5
Q

What is a supercluster?

A

Huge number of local groups then clusters held together by dark matter.

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6
Q

Which cluster do we belong to?

A

Virgo

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7
Q

1AU=

A

average distance from the Earth to the Sun
= 150 million km (150 000 000 km)
=1.5x10 to the eighth km

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8
Q

light year=

A

distance traveled by light in an Earth year.

9.46x 10 to the twelve km

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9
Q

light speed=

A

3 x 10 to the 8 m/sec

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10
Q

age of universe

A

13.7 billion years

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11
Q

When look at star 12 billion light years away how old is it?

A

Then the universe was only around 2 billion years old.

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12
Q

How can you weight the Sun?

A

By measuring the velocity of an object orbitting around it and the distance.

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13
Q

What’s the shortest time we consider and why?

A

10 to -43 seconds. Beacause that’s when physics began to work as it does today.

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14
Q

When did the Planck era take place and what happened?

A

before 10 to -43 sec.

Don’t have a theory to explain this period.

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15
Q

When did GUT era occur and what happened?

+temp

A

10 to -43 sec
temp 10 to 32 K
-Two forces operating, the GUT force and gravity (became separate from the rest here)

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16
Q

When did Electroweak era occur and what happened?

+ temp

A

10 to -38
10 to 29 K
Elementary particles appear spontaneously from energy and back. GUT force splits into electroweak and strong forces.
Huge expansion of the universe= inflation

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17
Q

When did Particle era happen and what occured?

+ temp

A

10 to -10
10 to 15 K - then the electroweak force splits into magnetic and the weak force= first time ever all four forces!
-elementary particles filling universe, then quarks combined to make protons and antiprotons.

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18
Q

When did Era of Nucleosynthesis happen and what took place?

+temp

A

0.001 s
10 to 12 K
-Fusion produces helium from protons (H nuclei)

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19
Q

When were nuclei formed?

+ temp

A

5 mins
10 to 9 K
fusion ceased, leaving normal matter 75% hydrogen 25% helium

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20
Q

When did atoms form?

+temp

A

380 000 years
3000K
Neutral atoms formed allowing photons to travel freely through space. Can’t see further than that.

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21
Q

What is normal matter also called?

A

Baryonic matter

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22
Q

What does WMAP do?

A

Measures the temperature and density of the early universe. -density of matter= where hot spots= where lot of dark matter is

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23
Q

Why is the universe expanding?

A

Because of dark energy.

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24
Q

Where do stars form?

A

In the densest regions of matter in clouds of gas and dust.

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25
How many motions does a person standing on the Earth experience?
6 - rotation of the Earth (1000km/h) - orbiting the Sun (100 000 km/h) - Sun moves with respect to the local stars (70 000 km/h) - The milky way moving towards Andromeda (800 000 km/h) etc. ..
26
What was the earliest recorded supernova?
RCW86 recorded in the Booh of Han in 185AD
27
When was Stonehenge built and possible purpose?
8000BC astronomical
28
What is the Antikythera Mechanism?
First analog computer capable of calculating moon phases, eclipses. Dated 100BC.
29
How did Eratosthenes measure the Earth?
knew from the angle difference Syene to ALexandria of the shadow at noon= 7. 7/360= distance to Syene=5000 5000x360 circumference of the Earth= 42 000 km modern value 40 100km.
30
Describe the Ptolemaic model of the Solar Sytem.
- geocentric, circular orbits - used for 1500 yrs - Arabic translation = Almagest(the greatest compilation)
31
Say something about Islamic astronomy.
- flourished 1025-1450 AD (until the fall of Constantinopole) - kept Greek astronomy alive - Developed doubts about geocentric view
32
What did Copernicus do?
Propose a Sun centered model not very accurate, still kept circular orbits.
33
What did Tycho do?
the observer, thought Earth the center but other planets go around the Sun
34
What did Kepler do?
-Sun centered system with elliptical orbits
35
What did Galileo do?
Scientific method,improved telescopes. | phases of venus-evidence for heliocentric model
36
Semimajor axis?
the horizontal one
37
semiminor axis?
vertical
38
Kepler's first law?
The orbit of each planet around the Sun is an ellipse with the Sun at one focus.
39
focus of an ellipse?
point from which we can draw sort of
40
Kepler's second law?
As a planet moves around its orbit, it sweeps out equal areas in equal times.= means that a planet travels slower when further from the Sun and faster when closer to the Sun.
41
Kepler's third law?
p2=a3 p-orbital period in years a-the semi-major axis of the orbit in AU
42
Describe Galileo's theory of relativity.
- free motion is constant in speed and direction - a freely falling body is constantly accelerating - a body sliding without friction down an inclined plane experiences constant acceleration - it is not possible to tell if vehicle is in constant motion
43
g=
9.8 m/sec2 so speed of a falling object increases 10 músec2 every 10 meters it falls (if no friction)
44
momentum=
mass x velocity - force changes momentum - spinning body= angular momentum
45
velocity
speed in a particular direction
46
speed
rate at which an object moves
47
acceleration
any change in velocity
48
mass
the amount of stuff
49
weight
the net force acting on a body (usually gravity)
50
Newton's first law of motion
An object moves at constant velocity unless a net force acts to change its speed or direction.
51
Newton's second law of motion
``` force= mass x acceleration or force= rate of change in momentum ```
52
Newton's third law of motion
For every force, there is always an equal and opposite reaction force.
53
Conservation of momentum
- total momentum of interacting objects cannot change unless an external force is acting on them - Interacting objects exchange momentum through equal and opposite forces
54
Conservation of angular momentum
= mass x velocity x radius - can't change unless external twisting force acting upon it - what keep planets orbiting the Sun - also when radius shrinks= faster rotation
55
temperature?
average kinetic energy of particles in a substance
56
thermal energy
collective kinetic energy of many particles | -depends on temperature and density (higher density= hoooot)
57
gravitational potential energy
on Earth depends on mass and gravity- distance an object could potentially fall -in space= object has more of this energy when spread out than when it contracts- if it contracts= converted to thermal energy
58
conservation of mass energy
E= mc2 - when Sun shines loses mass - concentrated energy can spontaneously turn into particles - mass and energy are the same thing
59
conservation of energy
- energy can neither be created nor destroyed - it can change forms or be exchanged between objects - the total energy was determined at Big Bang
60
Newton's Universal law of Gravitation
-every mass attracts every other mass Fg= Gx M1M2/d2 G-constant d=distance m=mass
61
bound orbit shape?
ellipse
62
unbound orbit shape
parabola or hyperbola
63
centre of mass
as momentum is conserved, orbiting objects orbit around their centre of mass
64
How can we weigh distant objects?
Kepler III, measure the mass by observing the period and measuring the separation of the two objetcts
65
what can change an object's orbit?
- friction or atmospheric drag | - gravitational encounter
66
what is escape velocity?
the energy needed to escape the gravitational pull of an object- changes orbit from bound to unbound Earth escape velocity -11km/s = 40 000km/h doesn't depend on the mass of an object
67
how does gravity cause tides?
-moon's gravity pulls harder on near side of Earth than on the far side -difference in Moon's gravitational pull stretches Earth -size of tide depends on the phase of the Moon (solar tidal force is 46% of the lunar one)
68
What is tidal friction and what does it cause?
As the Earth rotates and the moon around it= friction so it slows the Earth's rotation slowly -moon was out of sync in distant past now tidal friction keeps it almost constant
69
How much do tides vary?
Meditteranean 2-3cm, Bay of Fundy Nova Scotia= 15 m.
70
Why do all objects fall at the same rate?
Mass of object in Newton's second law exactly cancels mass in the law of gravitation.

Astronomy (6 decks)

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