Physics - space

Question 1

What is in our solar system?

Answer 1

Our solar system contains:
● The Sun (a star)
● Eight planets (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune)
● Dwarf planets (Pluto, Ceres and Eris are some examples)
● Natural Satellites (Moons)
● The asteroid belt (this exists between Mars and Jupiter)
● Comets are frozen rocks that move around the Sun in often very elliptical orbits

Question 2

Where is our solar system?

Answer 2

Our solar system is in the Milky Way galaxy, a collection of around 100 billion stars.

Question 3

How was our Sun formed?

Answer 3

The Sun formed about 4.5 billion years ago when a cloud of gas and dust (a nebula) was pulled together by gravitational attraction. The particles in the cloud got faster and collided more. The gas warmed up and eventually became hot enough to glow. This was a protostar. As the protostar gets more dense, more collisions take place and it gets hotter. Eventually the cloud gets hot enough for hydrogen atoms to fuse, forming helium. We call a star in this state a main sequence star.

Question 4

Why does the Sun remain in the main sequence stage?

Answer 4

In the main sequence stage, the gravitational attraction still pulling on the gas (actually a plasma) is balanced by the outward force of the radiation from the nuclear fusion in the core. We say the forces are
in equilibrium.

Question 5

Why do we have uranium?

Answer 5

Uranium and other such heavy elements naturally present on Earth can only be formed in a supernova explosion so the Sun must have formed from the remnants of a supernova.

Question 6

What is going to happen to our Sun eventually?

Answer 6

When a star starts to run out of hydrogen to fuse, its core collapses and the outer layers swell, cool down and the star will become a red giant. Here, helium and other light elements in the core fuse to form heavier elements. When there are no more light elements in the core, fusion stops and no more radiation is released. The star collapses, and as it does it turns from red to yellow to white becoming a white dwarf (much smaller than it was before). Such stars eventually fade out becoming black dwarfs.

Question 7

What would happen eventually if our Sun was much bigger?

Answer 7

Stars much bigger than ours become red supergiants then they collapse. Because there is more mass the collapse is more violent and a supernova explosion occurs. This is where elements heavier than iron can
form from fusion. The explosion compresses the core into a neutron star, an extremely dense object made only of neutrons. If the original star was massive enough, it becomes a black hole instead of a neutron star. The gravitational field of a black hole is so strong nothing can escape from it, not even light.

Question 8

Life cycle of a small star?

Answer 8

Nebula -> Protostar -> Main Sequence -> Red Giant -> White Dwarf -> Black Dwarf

Question 9

Life cycle of a larger star?

Answer 9

Nebula -> Protostar -> Main Sequence -> Super Red Giant -> Supernova -> Neutron Star OR Black Hole

Question 10

How do we decide if something is a planet, moon or satellite?

Answer 10

A planet orbits a star, enough gravity to make it spherical and sweeps out its own orbital path of other smaller objects.
A moon orbits a planet.
A satellite is something that orbits something else. The Moon is a natural satellite. There are many artificial (man-made) satellites.

Question 11

What provides the force that allows planets and satellites (natural and artificial) to maintain their circular orbit?

Answer 11

Gravity. It is an example of a centripetal force because it is acting towards the centre of a circle.

Question 12

Describe a circular orbit.

Answer 12

An object orbits another at a constant speed. Its direction is constantly changing so its velocity is changing (speed in a given direction). Therefore we say the object is accelerating towards the centre of the circle. The acceleration is a change of velocity per second.

Question 13

What happens to the orbit of an object if its speed changes?

Answer 13

If an object in orbit slows down, it will fall into a lower orbit (closer to the Earth). If it gets too slow, it will crash to the surface.
If an object in orbit speeds up, it will move to a higher orbit (further from the Earth). If it gets sufficiently fast it will escape the gravitational pull of the object it is orbiting and fly off into space.
At the correct speed an object will orbit at a constant height and speed.

Question 14

What is red-shift?

Answer 14

Light waves are stretched out if a star or galaxy is moving away from an observer. The wavelength of the light increases.This is called red-shift because the light is shifted towards the longer wavelength red end of the visible spectrum.
If a star or galaxy was moving towards the observer, the light waves would be compressed making the wavelength shorter and we would say the light has been blue-shifted.

Question 15

What is red-shift evidence for?

Answer 15

The faster a star or galaxy is moving away from an observer, the greater the effect of red-shift. Red-shift is observed in the large majority of galaxies so they are moving away from us and the more distant ones are moving away faster (speed of recession).
Edwin Hubble suggested that this meant that the universe is expanding because everything is moving away from everything else.

Question 16

What does the Big Bang theory suggest?

Answer 16

The universe is expanding and originated as a very small and extremely hot and dense region.
Red-shift provides evidence for this theory because at some point earlier in time the light must have been extremely short wavelength (high energy) and everything moving apart suggests everything came from
one centralised region.

Question 17

What other evidence is there for the Big Bang theory?

Answer 17

In 1965 scientists discovered microwaves coming from every direction in space. This microwave radiation
had been red-shifted suggesting that 13.5 (ish) billion years ago there must have been a massively energetic event in one place to still have evidence of it today. This radiation was called the Cosmic Microwave Background Radiation (CMBR).

Question 18

Were there any other theories for the origin of the universe?

Answer 18

The Steady State theory suggested that the universe was expanding, but it had always been there and matter was created into the spaces that the universe expanded into. More evidence was present for the Big Bang theory so that is why it is widely accepted today as being
the most probable origin story for the universe.

Question 19

What will happen to our universe?

Answer 19

Depending on the total mass of matter in the universe (unknown because we still have not observed dark matter, a strange substance that is needed for galaxies to maintain their shape) the universe could:
1. [If the universe is less dense than a certain amount] Expand forever, the stars will gradually die out and the universe will cool (Big Yawn)
2. [If the universe is more dense than a certain amount] Stop expanding and collapse (Big Crunch) - Some scientists currently think the universe has gone through cycles of this.