# Unit 5: Astronomy ## Terms - `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^oC|- Gleaming white, halo-like - extends millions of km into space| |Chromosphere|65 500^oC|| |Photosphere|5 500^oC|- 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. - Gives off **enormous amounts of energy**. ## Suns Affect on Earth ### The Aurora Borealis (Northern Lights) - 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. - `Northern Lights` = `Aurora Borealis`. - `Southern Lights` = `Aurora Australis`. ## The Solar System

### Planets 1. A planet must orbit a star 2. A planet must be big enough for its gravity to pull into a round shape 3. It must be big enough to clear most asteroids out of its path for its orbit. - If they can't do these things, it's not a planet, it's a dwarf planet. ### Drawf Planets - A celestial object that orbits the Sun and has a spherical shape but **does not** dominate its orbit. - Ceres, Pluto, Haumea, Makemake, and Eris - `Pluto’s` tilted orbit crosses Neptune’s orbit -

### The Inner Planets - Mercury, Venus, Earth & Mars. - Small rocky planets. - Located between the `Sun` and `Asteroid Belt`. |Planet|Orbital Period|Rotation|Atmosphere|Temperature|Number of Moons|Rings?|Unique Characteristics| |:-----|:-------------|:-------|:---------|:----------|:---------|:----|:---------------------| |Mercury|88 days|59 days|None|180 to 400^oC|0|No|- No atmosphere to trap heat
- Contains craters
- 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^oC|0|No|- Brightest object in the sky after the Sun & Moon| |Earth|365.26 days|24 hours|Nitrogen, Oxygen|-88 to 58^oC|1|No|- Ozone filters some of the damaging radiation from the Sun
- Temperatures are constant
- 70% of planet's surface is water| |Mars|687 days|24.65 hours|Carbon dioxide, Nitrogen|-90 to -5^oC|2|No|- Called the `red planet` due to its rusty soil
- Very dry
- 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^oC|63|Yes|- Largest planet (11x the diameter of the Earth)
- Features are its coloured bands, the Great Red Spot & hurricanes
- Orbiting rings of rocks| |Saturn|29.5 years|10.65 hours|Hydrogen, Helium, Methane|-178^oC|60|Yes|- Second largest, no solid core
- Cloudy & windy, over 1000 separate rings| |Uranus|84.1 years|17.3 hours `(on its side)`|Hydrogen, Helium, Methane|-216^oC|27|Yes|- Winds blow up to 500km/h| |Neptune|164.8 years|15.7 hours|Hydrogen, Helium, Methane|-214^oC|13|Yes|- Uneven orbit, Bright blue & white clouds
- 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. -

### Asteroid Belt - 700,000 to 1.7 million asteroids with a diameter of 1 km or more. - Over 200 asteroids are known to be larger than 100 km. -

### Comets - **`Comets`** are large chunks of `ice, dust`, and `rock` that orbit the Sun. - As a comet approaches the Sun, radiation and solar wind from the Sun, causes a `gaseous tail` to form, `pointing` directly `away` from the Sun. - A `dust` tail forms in the direction from which the comet originated. - Most comets have 2 tails; - `gaseous tail` - `dust tail` -

## Big Bang Theory - 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). -

### Low Mass Stars - 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**).
- Denser areas gather surrounding material due to greated **gravitational pull**
- As material is added, gravity increases , drawing in even more material… then density and pressure increase as well.
- This core and surrounding material start spinning more as they continue to condense. (like a figure skater)
- 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)
- **Temperature begins to rise** due to atomic collisions and start emitting **low level energies like microwave & infrared**.
- This is now called a protostar.|

| |2. Main sequence phase (adult star)|- As core temperature reaches a critical point (15 million °C), **NUCLEAR FUSION begins** and it becomes a *star**.
- H atoms join to form He atoms, releasing enormous amounts of **high energy radiation**, which also **emits light energy.**|

| |3. Old Age|- Once a star’s core has **used up its H**, it fuses **He**, which **releases even more energy**.
- This causes the star to swell into a **red giant** or **red supergiant** depending on their original mass.|

| |4. Death|- An average star “dies” when it doesn’t have enough energy to continue **nuclear fusion** (usually once it forms **carbon**).
- For a star like our sun, the core shrinks/collapses, releasing the outer layers of gases.
- 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**.
- 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**.|

| |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**.
- **Large red giants** explode as a **supernova**, & will form either a **neutron star** or even a **black hole** if the core has enough mass.|

## Space Composition -

### Dark Matter - 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!