AST MT1 - Tides and The Sun

Lesson 7 and 8

What is the relationship between the Earth and Moon in relation to gravity?

• Gravitational attraction between the Earth and Moon applies a force on different parts of the Earth

• Side closest to Moon = strong attraction

• Side opposite of Moon = weakest attraction

What affect does differential forces have on the shape of the Earth and Moon?

It causes them to stretch into an oblate spheroid, similar to a football.

• However, since the Earth rotates too quickly, the rock and mantle don’t have enough time to respond and reshape

How does differential force cause tides?

• The waters in the ocean experience small horizontal tugs

• These tide-raising forces produce motions of the water that result in tidal bulges

• Water on the side facing and opposite of the Moon flows towards it

How many tides do we experience per day?

Two high tides and two low tides.

What are spring tides?

When the Sun and Moon are aligned and their tides reinforce each other, causing the tides to be greater than usual.

What are neap tides?

When the Moon is at its first or last quarter and the Sun’s tides partially cancel the Moon’s, making them smaller.

What is tidal locking?

When the rotation of a celestial body becomes synchronized with its orbital period around a larger body, causing the same face to always be presented to the larger.

How is the Moon tidal locked?

Tidal force on the Moon by Earth is much larger than the tidal force on Earth by the Moon, since the Moon has already stopped relative to Earth, it’s tidal locked.

Why is the sunset red and the sky blue?

• White light (all colours) is emitted from the Sun

• The atmosphere scatters blue light around, causing a person to see a blue sky and white Sun

• Red light makes it through the atmosphere unscattered, so a person sees a red Sun

What does a helium atom consist of?

• Two protons

• Two neutrons

• Two electrons

What does a hydrogen atom consist of?

• One proton

• Zero neutrons

• One electron

If you were to fuse protons (super hard), what would be the result?

• Two positrons

• Two neutrinos

• Two gamma-rays

• One helium-3 nucleus

• These all have lower mass than which was started with 

Where did the remaining mass in the fusion go?

It became energy according to Einstein’s equation, E = mc².

How can you get protons to fuse together?

Temperature and density need to be high in order for the protons to stick and fuse together.

• The Sun’s core is millions of degrees and 160x denser than water

How can you achieve higher pressure?

• Higher temp = moving faster

• Higher density = more particles

What is the equilibrium in terms of the Sun?

All forces within it are balanced so that the temperature, pressure, density, etc. are maintained at constant values.

How can the equilibrium be restored if the density is above equilibrium?

Density above equilibrium > rate of fusion increases > temp increases > pressure increases > core expands > density drops > equilibrium restored

Define “nuclear fusion”

When light atomic nuclei come together to form a heavier one.

Define “nuclear fission”

When heavy atomic nuclei break up into lighter ones.

Provide an example of nuclear fission

²³⁵U has 92 protons and 143 neutrons > neutron hits it > becomes ²³⁶U, which is unstable > strong force can’t hold it together > breaks up into smaller pieces > some mass converted into energy

Describe the core of the Sun

• 10 million degrees C

• Where fusion takes place

• 100x the density of water

Describe the radiative zone of the Sun

• Few million degrees C

• Similar density to water

Describe the convection zone of the Sun

• Hundreds of thousands of degrees C

• Contains hot plasma

• Density of styrofoam

What is plasma?

The result of electrons being stripped away from the nucleus of a helium atom at high temperatures.

What are sunspots?

Cooler (4000 C) spots on the surface of the Sun.