# Episode 4: A Sky Full of Ghosts Flashcards

1
Q

Explain how the night sky is full of ghosts?

A

Every star is as big and bright as our own star, the sun. Light travels fast but not infinitely fast. It takes time for the light from the stars to reach us. For the nearest stars ones it takes eons to reach earth. By the time the light reaches earth some stars are already dead

2
Q

Who was the first person to understand that a telescope is a time machine?

A

William Hershel was the first person to understand that a telescope is a time machine. We cannot look into space without seeing back in time

3
Q

How far does light travel in 1 second?

A

In 1 second light travels 300,000kms

4
Q

How far away is the moon from the earth?

A

The moon is just over 300,000kms from earth so it is 1 light second from earth. Whenever we look at the moon we are seeing it one second in the past

5
Q

Why is the sunrise an illusion?

A

The earths atmosphere bends the suns light like a lens or a glass of water. We see the image of the sun projected on the horizon before the sun is actually there

6
Q

How long does light take to get from the sun to earth?

A

Sunlight takes about 8 minutes to reach earth so the sun is 8 light minutes from earth. From earth we can only see the sun as it was 8 minutes ago

7
Q

How far away is neptune from earth?

A

Neptune is 4 light hours away from earth. We can only view neptune as it was 4 hours ago

8
Q

How far is a single lightyear in kilometres?

A

A single lightyear is nearly 10 trillion kms

9
Q

What is the nearest star to the sun and how far away is it?

A

The nearest star to our sun is Proximus Centuri and it is a little more than 4 lightyears away

10
Q

How fast does voyager travel?

A

Voyager travels at more than 56,000kms per hour. It will take voyager 80,000 years to reach the nearest star

11
Q

How far away is the Pleiades Cluster?

A

The Pleiades Cluster is approximately 400 lightyears away

12
Q

What is the Crab Nebula?

A

The Crab Nebula was once a giant star 10 times the mass of the sun. It exploded as a supanova and now at its heart is pulsar, a collapsed star the size of a city spinning 30 times a second. It’s magnetic field excites electrons around it accelerating them to almost the speed of light which makes them shine with a blue glow. The Crab Nebula is 6500 lightyears away from earth

13
Q

How far away is the earth from the centre of the galaxy?

A

The centre of the galaxy is 30,000 light years from earth

14
Q

How old is the light we can see from the Sombrero galaxy?

A

The light we can see from the Sombrero galaxy is 30 million years old

15
Q

How far away from earth is the Coma Cluster?

A

The Coma Cluster is 320 light years away

16
Q

What is the oldest light we have ever detected in our universe?

A

The oldest light we have ever detected is 13.4 billion years old detected by the Hubble telescope

17
Q

Where are we in the universe?

A

No matter which galaxy you view from you will find yourself at the very centre of the cosmic horizon. But this is just an illusion.It’s what you get when you have a finite speed of light in a universe that had a beginning in time.

18
Q

What made possible the formation of the planets and ultimately life?

A

As the first generation of stars died they seeded the universe with heavier elements making possible the formation of planets and ultimately life?

19
Q

What was created in the big bang?

A

Matter and energy were created in the big bang as was space and time and all forces that bind it together

20
Q

Who discovered that Newton’s formulas of gravity also rule the distant stars?

A

100 years after Newton published his formulas of gravity William Hershel discovered that it also rules the distant stars. Gravity’s empire governs all the heavens

21
Q

What was Michael Faraday’s discovery that related to gravity?

A

Michael Faraday discovered in the 19th century that we are surrounded by invisible fields of force that explained how gravity works. The apple and the earth don’t touch each other but the fields between them do. He imagined those lines of gravitational force radiating out into space from every massive body

22
Q

In 1865 what did James Clarke Maxwell do?

A

In 1865 James Clarke Maxwell translated Faraday’s ideas about fields of electricity and magnetism into mathematical laws. He discovered that these fields move through space in waves. When he calculated how fast these waves move it turned out to be the speed of light

23
Q

Who did Einstein keep portraits of on his walls in his lab?

A

Einstein kept portraits of Michael Faraday and James Clarke Maxwell on the wall of his laboratory as he knew he was standing on their shoulders

24
Q

What is wrong with the way we calculate speed?

A

We have always calculated speed in relation to something that isn’t moving. The problem with this is finding something in the cosmos that isn’t in motion

25
Q

How fast are you moving when cruising on a bicycle?

A

If your moving at 10km/h in relation to the ground, the ground is moving at 1600km/h as the earth is spinning. Also the earth is orbiting the sun at 108,000km/h and the sun is traveling through the galaxy at more than 700,000km/h. On top of this the milky way is moving through the universe at nearly 2.5million km/h!

26
Q

Where is there a fixed place in the universe?

A

There is no fixed place in the cosmos, all of nature is in motion

27
Q

What can you change by giving a child a book?

A

Give a child a book and you change the world, maybe even the universe. Einstein was given a book as a small boy describing the astonishing speeds at which electricity travels through wires and light through space. This triggered his curiosity about the universe and how you would perceive the universe if traveling at the speed of light

28
Q

What are the rules that must be obeyed when travelling from high speeds?

A

The principles of relativity

29
Q

Why is the speed of light any more a barrier than the speed of sound?

A

The answer is not just that light travels about a million times faster than the speed of sound and not merely just an engineering problem. The light barrier is a fundamental law of nature

30
Q

How fast does light travel in relation to its source?

A

Light travels just as fast no matter how fast or slow its source is moving. The speed of light is constant. Thou shalt not add my speed to the speed of light

31
Q

What material objects can travel at the speed of light?

A

No material object can travel at or faster than the speed of light. There is nothing in physics that prevents you from traveling as close to the speed of light as you like. For reality to be logically consistent there must be a cosmic speed limit. Thou shalt not move faster than the speed of light

32
Q

Who was John Mitchell?

A

John Mitchell lived in England in 18th century. Mitchell imagined a star so big with gravitational force so strong nothing, not even light, can escape its grasp. He predicted we may be able to detect dark stars by their gravitational footprints. Today we call these Black Holes

33
Q

What bows to gravity at millions of Gs of force?

A

At millions of Gs everything, even light, bows to gravity

34
Q

How many stars have the potential to become a black hole?

A

1 in every 1000 stars is massive enough to become a black hole

35
Q

How do black holes form?

A

When giant stars exhaust their nuclear fuel they can no longer stay hot enough to fend off the inward pull of their own gravity. The most massive stars collapse into darkness only leaving behind the force of their gravity

36
Q

What do we call the boundaries that separate black holes from the rest of the universe?

A

The boundary that separates a black hole from the rest of the universe is called an event horizon. From our point of view objects approaching the event horizon slow down never quite reaching it

37
Q

What was the first black hole ever discovered called?

A

The first black hole ever discovered was named Cygnus X1. It is 64km across and was found using x-ray sensitive telescopes that could see the discs of gas that circle the black hole that heat to over 100 million degrees

38
Q

What is theorised to be at the centre of our galaxy?

A

A Super Massive Black hole. The stars nearest our galaxy whip around at nearly 40 million km/h. What could make them move so fast? Something with a mass of 4 million suns. But where is the blazing light of 4 million suns? Since we cant see it it must be imprisoned inside a super massive black hole

39
Q

What has been detected in every galaxy?

A

A super massive black hole

40
Q

Who built on William Hershel’s deep space observations?

A

John Hershel built on his father’s observations and they became the basis for the standard catalogue of galaxies that we use today

41
Q

What did John Hershel seek?

A

John Hershel sought a way to preserve the past and to capture light and memories. During this pursuit he succeeded and discovered a new form of time travel…photography