-`AU` = Astronmical Unit, which is the distance between the sun and the Earth = $`1.5 times 10^8`$
-`1 Light year` = $`9.46 \times 10^{12}`$
- Our milky way is a spiral yeet (forgot full lesson, think this is all you need).
## Layers of the Sun
|Layer|Temperature|Description|
|:----|:----------|:----------|
|Corona|5800<sup>o</sup>C|- Gleaming white, halo-like - extends millions of km into space|
|Chromosphere|65 500<sup>o</sup>C||
|Photosphere|5 500<sup>o</sup>C|- The layer just below the Chromosphere where the light we see originates|
## Inside Of The Sun
|Zone|Descrption|
|:---|:---------|
|Convection Zone|- The `outermost` ring of the sun, comprosing of the `30` percent of its radius|
|Radiative Zone| - The section immediately `surrounding` the core, comprising `45` percent of its radius|
### Core
-`Hottest` part of the sun, reaching $`15,000,000^o`$C
- Energy released by **nuclear fusion** continues to move outward until it reaches the photosphere
- #### Compostion
- **75%** `hydrogen`
- **25%** `helium` (with small amounts of other gases)
### Nuclear Fusion
- The sun is made out of **hydrogen** atoms.
- The Sun’s energy comes from the **nuclear fusion** reactions that occur in the **core** of the Sun.
- **High temperatures** and **pressure** cause particles to collide at extremely high speeds. The **hydrogen** atoms of the sun fuse together forming **helium** atoms.
- The `Northern Lights` are the result of collisions between gaseous particles in the Earth's atmosphere with charged particles released from the sun's atmosphere.
-`Solar winds` travelling toward Earth follow the lines of `magnetic force` created by Earth’s magnetic field (which is strongest near the **NORTH** and **SOUTH**`poles`).
- Near the poles, they come in contact with particles in Earth’s atmosphere, producing a display of `light` in the night sky.
|Mercury|88 days|59 days|None|180 to 400<sup>o</sup>C|0|No|- No atmosphere to trap heat<br>- Contains craters<br>- Rarely visible in our night sky because its is so close to the sun|
|Venus|224.7 days|243 days, `(Opposite rotation)`|Carbon dioxide, nitrogen|462<sup>o</sup>C|0|No|- Brightest object in the sky after the Sun & Moon|
|Earth|365.26 days|24 hours|Nitrogen, Oxygen|-88 to 58<sup>o</sup>C|1|No|- Ozone filters some of the damaging radiation from the Sun<br>- Temperatures are constant<br>- 70% of planet's surface is water|
|Mars|687 days|24.65 hours|Carbon dioxide, Nitrogen|-90 to -5<sup>o</sup>C|2|No|- Called the `red planet` due to its rusty soil<br>- Very dry<br>- Once had volcanoes, glaciers, & water|
### The Outer Planets
- Jupiter, Saturn, Uranus, Neptune
-`Large`, composed of `gas`.
- Atopsheres consist mainlyof the gases `hydrogen` and `helium`.
|Planet|Orbital Period|Rotation|Atmosphere|Temperature|Number of Moons|Rings?|Unique Characteristics|
|Jupiter|11.9 years|9.85 hours|Hydrogen, Helium, methane|-148<sup>o</sup>C|63|Yes|- Largest planet (11x the diameter of the Earth)<br>- Features are its coloured bands, the Great Red Spot & hurricanes<br>- Orbiting rings of rocks|
|Saturn|29.5 years|10.65 hours|Hydrogen, Helium, Methane|-178<sup>o</sup>C|60|Yes|- Second largest, no solid core<br>- Cloudy & windy, over 1000 separate rings|
|Uranus|84.1 years|17.3 hours `(on its side)`|Hydrogen, Helium, Methane|-216<sup>o</sup>C|27|Yes|- Winds blow up to 500km/h|
|Neptune|164.8 years|15.7 hours|Hydrogen, Helium, Methane|-214<sup>o</sup>C|13|Yes|- Uneven orbit, Bright blue & white clouds<br>- Has a dark region called the Great Dark Spot, which appears to be the center of a storm|
### Asteroids
- They are composed of rock & metal.
- Although they orbit the Sun, they are too small to be considered planets.
- Most asteroids lie in the asteroid belt, located between Mars & Jupiter.
- A **`meteroid`** is a piece of metal or rock that is `smaller` than an asteroid.
- Sometimes a meteroid get pulled in by `Earth's gravity`. They `burn` up in the Earth's `atmosphere`, creating a bright streak of `light` across the sky, know as **`meteor`** (shooting star).
- Larger meteors do not burn up completely in the atmosphere and their `remains`, which we call **`meteorites`**, crash to the ground.
- It happened around 13.7 billion years ago when the Universe was a infintely dense point.
- Formed from an extremely dense singularity (centre of a black hole)
- Prior to that there was nothing
### Evidence to support theory
- #### Redshift and Hubble’s Law
- Hubble observed the line spectra from many different galaxies in sky, and most of spectra for galaxies were shifted towards the red end of the spectrum, a red shift
- Hubble concluded that if most of galaxies were redshifted, they must be moving in all directions and the Universe is expanding from a single point
- Space between galaxies expand, not the galaxies themselves
- **Dark Matter:** the rest of the Universe appears to be made of a mysterious, invisible substance called dark matter (25%) and a force that repels gravity known as dark energy (70%)
- 90% of matter in and between galaxies is of an unknown form that does not emit or absorb light
- Can be detected through its gravity by the way it affects objects we can see
- Without dark matter, normal matter would have been unable to clump and form stars and galaxies
## Apparent and Absolute Magnitude
-`Luminosity`: Total amount of energy produced by a star per second
-`Apparent Magnitude`
- Brightness of a star in the night sky as they appear on Earth
- The lower the number, the brighter the star is
-`Absolute Magnitude`
- Brightness of a star as if they were located 33 ly from Earth
- The lower the number, the brighter the star is
## Size of stars changes their lifestyle
### Hertzsprung Russel Diagram
- The Hertzsprung-Russell Diagram is a graphical tool that astronomers use to classify stars according to their luminosity, spectral type, color, temperature and evolutionary stage.
- Basically plotting the class of the stars based on their lumionsity (how bright they are) and their temperature (how hot they are).
- With less gravity, burns hydrogen fuel slowly and lasts for 100 billion years, matures into red dwarf, and when fuel for nuclear fusion runs out, becomes a white dwarf
### Medium Mass Stars
- Lasts for 10 billion years
- When a medium mass star runs out of fuel, it collapses under its own gravity, collapse heating up and pressure increases causing nuclear fusion of helium
- Star expands and becomes a red giant, eventually burning out to form a white dwarf
- When white dwarfs become cool enough to no longer emit heat or light, they become black dwarfs, however since the time required for a white dwarf to reach this state is older than the Universe, no black dwarfs currently exist
### High Mass Stars
- Lasts up to 7 billion years, 10 times size of our Sun
- When high mass star runs out of fuel it collapses and expands to form a supergiant
- Supergiants end in a violent massive explosion called a supernova
- End results - Cosmic debris (nebula), a neutron star (or pulsar) or a black hole
### Supernova
- Supergiants that run out of fuel end in a massive explosion
- Nuclear fusion reactions occur and new elements form and explode into space
- Debris from explosion is source for a new nebula, and what happens to the stars remaining core depends on original size of the star
### Neutron Stars
- Remaining core of a supergiant that is less than 40 times the size of our Sun
- Also called a pulsar, very dense matter made of neutrons
## Black Holes
- Remaining core of a supergiant that needs to be more than 40 times the size of our Sun
- Core of the supergiant after a supernova is so dense that its gravitational pull sucks in space, time, light, and matter
- Thought to be at the centre of all galaxies
## Formation of Stars
|Stage|Description|Picture|
|:----|:----------|:------|
|1. Birth and Early Life|- Life for a star begins in a **nebula**, which are HUGE, unevenly distributed clouds of dust and gases (**mainly H** &**He**).<br>- Denser areas gather surrounding material due to greated **gravitational pull**<br>- As material is added, gravity increases , drawing in even more material… then density and pressure increase as well.<br>- This core and surrounding material start spinning more as they continue to condense. (like a figure skater)<br>- Any surrounding dust and gases that aren’t drawn into the core will **flatten out** to look like a disc around the core. (the natural tendency for all spinning objects)<br>- **Temperature begins to rise** due to atomic collisions and start emitting **low level energies like microwave & infrared**.<br>- This is now called a protostar.|<imgsrc="https://www.myastroshop.com.au/guides/vc200l/helix-judge-s.jpg"width="500">|
|2. Main sequence phase (adult star)|- As core temperature reaches a critical point (15 million °C), **NUCLEAR FUSION begins** and it becomes a *star**. <br>- H atoms join to form He atoms, releasing enormous amounts of **high energy radiation**, which also **emits light energy.**|<imgsrc="https://lifecycleofstarsscience.weebly.com/uploads/1/8/8/2/18823332/2663663_orig.jpg?363"width="500">|
|3. Old Age|- Once a star’s core has **used up its H**, it fuses **He**, which **releases even more energy**. <br>- This causes the star to swell into a **red giant** or **red supergiant** depending on their original mass.|<imgsrc="https://images.newscientist.com/wp-content/uploads/2018/01/18185636/gettyimages-648917144-800x533.jpg"width="500">|
|4. Death|- An average star “dies” when it doesn’t have enough energy to continue **nuclear fusion** (usually once it forms **carbon**). <br>- For a star like our sun, the core shrinks/collapses, releasing the outer layers of gases. <br>- The `small, hot, and dense core` becomes a **white dwarf**, while the outer gases form a new **nebula** around it. This combo is called a **planetary nebula**. <br>- A more massive star will do fusion up until **iron** then collapse, but the outer layers will explode off this iron core to form a **supernova**.|<imgsrc="https://i.ytimg.com/vi/aysiMbgml5g/maxresdefault.jpg"width="500">|
|5. Remains|- **Small red giants** collapse & shrink into a **white dwarf**, which will slowly cool down and eventually **fade out** (no energy emitted) to be a **black dwarf**.<br>- **Large red giants** explode as a **supernova**, & will form either a **neutron star** or even a **black hole** if the core has enough mass.|<imgsrc="https://fortunedotcom.files.wordpress.com/2019/04/first-image-of-black-hole-national-science-foundation.jpg"width="500">
- The rest of the universe appears to be made of a mysterious, invisible substance called dark matter (25 percent) and a force that repels gravity known as `dark energy` (70 percent). Scientists have not yet observed `dark matter` directly.
-`90%` of matter in and `between` galaxies is of an `unknown` form that `does not emit or absorb light (so we can’t see it)`.
- It can be detected through its `gravity` by the way it `affects` objects we can see.
- Without dark matter, `normal matter` would have been unable to `clump` and `form` stars and `galaxies` - and US!
