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Astronomy > Lectures 1-6 > Flashcards

Lectures 1-6 Flashcards

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
Q

How many motions does a person standing on the Earth experience?

A

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. ..
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26
Q

What was the earliest recorded supernova?

A

RCW86 recorded in the Booh of Han in 185AD

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27
Q

When was Stonehenge built and possible purpose?

A

8000BC astronomical

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28
Q

What is the Antikythera Mechanism?

A

First analog computer capable of calculating moon phases, eclipses. Dated 100BC.

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29
Q

How did Eratosthenes measure the Earth?

A

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
Q

Describe the Ptolemaic model of the Solar Sytem.

A
  • geocentric, circular orbits
  • used for 1500 yrs
  • Arabic translation = Almagest(the greatest compilation)
31
Q

Say something about Islamic astronomy.

A
  • flourished 1025-1450 AD (until the fall of Constantinopole)
  • kept Greek astronomy alive
  • Developed doubts about geocentric view
32
Q

What did Copernicus do?

A

Propose a Sun centered model not very accurate, still kept circular orbits.

33
Q

What did Tycho do?

A

the observer, thought Earth the center but other planets go around the Sun

34
Q

What did Kepler do?

A

-Sun centered system with elliptical orbits

35
Q

What did Galileo do?

A

Scientific method,improved telescopes.

phases of venus-evidence for heliocentric model

36
Q

Semimajor axis?

A

the horizontal one

37
Q

semiminor axis?

A

vertical

38
Q

Kepler’s first law?

A

The orbit of each planet around the Sun is an ellipse with the Sun at one focus.

39
Q

focus of an ellipse?

A

point from which we can draw sort of

40
Q

Kepler’s second law?

A

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
Q

Kepler’s third law?

A

p2=a3
p-orbital period in years
a-the semi-major axis of the orbit in AU

42
Q

Describe Galileo’s theory of relativity.

A
  • 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
Q

g=

A

9.8 m/sec2
so speed of a falling object increases 10 músec2 every 10 meters it falls
(if no friction)

44
Q

momentum=

A

mass x velocity

  • force changes momentum
  • spinning body= angular momentum
45
Q

velocity

A

speed in a particular direction

46
Q

speed

A

rate at which an object moves

47
Q

acceleration

A

any change in velocity

48
Q

mass

A

the amount of stuff

49
Q

weight

A

the net force acting on a body (usually gravity)

50
Q

Newton’s first law of motion

A

An object moves at constant velocity unless a net force acts to change its speed or direction.

51
Q

Newton’s second law of motion

A 
force= mass x acceleration or
force= rate of change in momentum
52
Q

Newton’s third law of motion

A

For every force, there is always an equal and opposite reaction force.

53
Q

Conservation of momentum

A
  • 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
Q

Conservation of angular momentum

A

= 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
Q

temperature?

A

average kinetic energy of particles in a substance

56
Q

thermal energy

A

collective kinetic energy of many particles

-depends on temperature and density (higher density= hoooot)

57
Q

gravitational potential energy

A

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
Q

conservation of mass energy

A

E= mc2

  • when Sun shines loses mass
  • concentrated energy can spontaneously turn into particles
  • mass and energy are the same thing
59
Q

conservation of energy

A
  • 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
Q

Newton’s Universal law of Gravitation

A

-every mass attracts every other mass
Fg= Gx M1M2/d2
G-constant d=distance m=mass

61
Q

bound orbit shape?

A

ellipse

62
Q

unbound orbit shape

A

parabola or hyperbola

63
Q

centre of mass

A

as momentum is conserved, orbiting objects orbit around their centre of mass

64
Q

How can we weigh distant objects?

A

Kepler III, measure the mass by observing the period and measuring the separation of the two objetcts

65
Q

what can change an object’s orbit?

A
  • friction or atmospheric drag

- gravitational encounter

66
Q

what is escape velocity?

A

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
Q

how does gravity cause tides?

A

-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
Q

What is tidal friction and what does it cause?

A

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
Q

How much do tides vary?

A

Meditteranean 2-3cm, Bay of Fundy Nova Scotia= 15 m.

70
Q

Why do all objects fall at the same rate?

A

Mass of object in Newton’s second law exactly cancels mass in the law of gravitation.

Astronomy (6 decks)

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