space unit grade 9
Our Sun
Sun is a star described as a dwarf star, meaning it's pretty small
The star in our solar system is the Sun
It is a G-type star
110 Earths could fit across the suns diameter
1.3 million Earths could fit inside the sun
An object at the Sun's surface would weigh 28 times as much as it does on the Earth's surface
The surface of the sun is 5500 °K or 5315 °C
The suns core temperature is 15 million °K
This is hot enough to achieve nuclear fusion for hydrogen
The sun’s energy comes from
Nuclear fusion is the fusing of atomic nuclei to form larger nuclei
This reaction can release incredible amounts of Energy in to from of light, heat, and other forms of emergy
The sun converts about 400 million tonnes of hydrogen into helium per second
Just 1 tonne would create enough energy for 700,000 Americans to live for 1 year
It is believed that the sun is 5 billion years old and will burn for another 5 billion years
Core is 15 million °C, and nuclear fusion occurs here
The radiative zone extends ¾ of the way up to the surface of the sun. Light takes 100000 years to pass up and through it
The convective zone is where plasma moves up and down in a convection motion
The photosphere is the boundary between the inside and the outside of the sun. It is the coolest layer at 5500 °C
The chromosphere is the layer that looks red, but because of the bright photo sphere can only be seen during a solar eclipse
The corona is the outermost layer of the sun
Sunspots are regions that can be cooler because convection is slowed down by magnetic forces
Prominences are large, often curved streams of particles from the phototsphere it is shaped by the magnetic field
Solar flares are massive explosions from the surface, seen as lon bright filament caused by the magnetic field of the sun breaking through the surface
A coronal mass ejection is a huge solar flare. The plasma can reach the earth but we are protected by our magnetic field. It can damage satellites and electrical transmission lines
How does the sun affect Earth
The sun provides energy for all living organisms
Solar flares cause auroras at the poles
When solar flares occur, energy from the sun energizes the atoms in the atmosphere of the earth which give off visible light
It occurs at the poles because of the interference of the Earth's magnetic field there
Objects within the Solar System
The primary regions of the solar system are
The inner solar system
The 4 planets in the inner solar system are Mercury, Venus, Earth and Mars
The asteroid belt
A region of space between the orbits of Mars and Jupiter
Contains the dwarf planet Ceres, plus as many as tens of thousands or perhaps even millions of objects of 1km
Despite this, it is unlikely tbe total mass of the entire asteroid belt exceeds one thousandth of the mass of Earth
The outer solar system
The 4 planets in the outer solar system are Jupiter, Saturn, Uranus and Neptune
The Kuiper belt
A region of space that is outside the orbit of Neptune it is between 30AU and 50AU
1AU is the average orbital distance between the Earth and the sun
Contains dwarf planets Pluto, Haumea and Makemake
The overall mass og the Kuper belt likely still doesn't exceed 1/10 that of the earth
While manmy Kupier belf objects are rocky like the asteroid belt objects, most of them are actually composed of frozen volatiles like methane, ammonia and water
Some often confuse the Kuiper belt with the origin of comets
The Oort cloud is a theorized region of space at about 1 to 1.8 light-years
It is believed to surround the sun in a spherical formation and is believed to contain trillions of small, slowly moving comets
Planets
A planet is defined as an object
It is massive enough to be rounded by its own gravity
Not massive enough to support the thermonuclear fusion
Th have established itself such that it has swept its orbit clear of smaller bodies
Terrestrial planets are fundamentally similar to earth meaning they are mostly composed of rock (Mercury, Venus, Earth and Mars)
Gas Giants are plants primarily composed of hydrogen and helium (Jupiter and Saturn)
Ice giants are planets mostly composed of water, methane and ammonia (Uranus and Neptune)
Pluto qualifies as a planet according to the first 2 crieterias, but the orbit has not been swept clear of debris, so now it is considered a dwarf planet
A dwarf planet is an object which orbits the sun directly but hasn't swept clear of debris (Eris, Pluto, Haumea, Makemake, Ceres)
Moons
Many planets have natural satellites called moons
A moon is a body that does not orbit the sun directly but orbits a planet
Only 2 planets, Mercury and Venus, have no natural satellites
Earth's satellite is called Luna
Comets
Comets are small icy solar system objects
They often have eccentric orbits passing near the sun and far away
There are many comets, typically about 1 is visible a year
As comets closely approach the sun, some of the ice is transformed into gases, which leave a very visible tail which sweeps away from the body of the comet
Distances in Space
Kilometers
Things are so far apart in space that kilometres become unwieldy and hard to visualize
The distance from the sun to Earth is 149600000
Astronomical Unit
Astronomical Units can be used to measure distances in our solar system
AU is the average distance between the Earth and the Sun
Light Years
Light-years are a more common unit used in astronomy
The speed of light is 299,792 km per second
A light-second is 299,792 km
It ishow far light can travel in 1 second
Light can travel around the Earth 7.5 times in 1 second
One light-minute is 17,987,520 km
One light-minute is how far light travels in one minute
The sun is 8 light minutes away
One light-hour is 107,900,000 km
One light-hour is how far light travels in one hour
Pluto is 4-7 light hours away
The nearest star is Proxima Centauri at 4.2 light-years
It would take the space probe Voyager, travelling at 38,000 mp/h 76,000 years to get there
Betelgeuse is 1400 light-years away
Our galaxy, the Milky Way, is 94,600,000,000,000 km
Our neighbouring galaxy andromeda is estimated at 2,400,000 light-years away
Life Cycle of Stars
Birth of a star:
Stars are born in nebulae, which are clouds of gas and dust
Gravity in the nebula pulls together the gas and dust
A protostar is formed
Once the protostar’s temperature rises high enough to undergo thermonuclear fusion, a star is born
HR Diagram
The x-axis is the surface temperature in K
The y-axis is luminosity compared to the sun
Spectral Classification of Stars:
Spectral Classification | Apparent Colour | Surface Temperature | Mass | % of all stars | Lifespan |
O | Blue | >30,000 | >16 | ~0.00003% | 2-8 million |
B | Blue-White | 10,000-30,000 | 2.1-16 | 0.13% | ~10-100 million |
A | White | 7,500-10,000 | 1.40-2.1 | 0.6% | 400 million |
F | Yellow-White | 6,000-7,500 | 10.4-1.4 | 3% | ~5 billion |
G | Yellow | 5,200-6,000 | 0.80-1.04 | 7.5% | ~10 billion |
K | Orange | 3,700-5,200 | 0.45-0.80 | 12.1% | ~15 billion |
M | Red | 2,400-3,700 | 0.08-0.45 | 76.45% | Possibly as much as 12 trillion |
Along the diagonal from the top left to the bottom right runs the main sequence
All stars spend the main part of their normal life in the main sequence
Stars located on the main sequence are called dwarf stars
The sun is a G-type star
The top right side of the main sequence has various sub-giant, gian and super-giant stars and hypergiant stars
These stars are in their old age
The bottom to the left of the main sequence has the white dwarf stars
These stars have died, but still have some heat in them, so they still glow.
Things to Note
Generally, the larger the star is:
The hotter it is
The brighter it is
The shorter its lifespan
If a star has a lot of mass, then this compresses the core of the star, increasing the pressure inside and therefore pushing the hydrogen atoms closer together
This increases the rate at which fusion occurs
Why Does a Star Die?
As a star lives its life, it fuses hydrogen atoms together to make helium atoms
This generates the energy that fuels the star
As hydregen fuses, the amount of fuel available reduces over time
Eventually, the star runs out of hydrogen fuel
When a star runs out of fuel, what happens depends on the mass of the star
Low Mass Stars (<0.5 Msun)
These stars burn hydrogen until the majority of the star is helium
At this point, the star begins to collapse because there is no outward pressure provided by the energy being produced by fusion
The star shrinks until the atoms of the star are pressed very tightly together
At this point, if the star were to compress more, it would force 2 electrons to occupy the same location in the Bohr-Rutherford diagram
This produces an outward pressure called electron degeneracy pressure, which halts the collapse of a star
The result is a white dwarf.
This white dwarf is still quite hot because of the residual heat from the star's early life, but it cools down over time
Mid-Mass Stars (0.5 Msun to 10 Msun)
When these stars run out of hydrogen fuel, they instead go through a phase where they begin to fuse helium into larger elements
This causes the star to expand into a red giant
When the sun finally runs out of helium fuel (in a relatively short amount of time), the star will then have a core of carbon, which begins to cool and collapse into a white dwarf
High-Mass Stars (>10 Msun)
When these stars run out of hydrogen fuel, they begin to fuse helium and then move on to fusing heavier and heavier elements, producing carbon, oxygen, silicon, iron and the other elements lighter than iron in lesser quantities
When the core is iron, the shell will begin to fall inwards, then it rebounds off the star's core, causing a huge explosion called a supernova
Supernova
During the explosion of a supernova, massive forces are at work. The excess of energy makes it possible for iron to fuse into heavier elements despite the fact that energy is lost in the process
All the elements on the periodic table we studied in chemistry are made during the brief process of a supernova
The fact that there are heavier elements here on Earth is evidence that our star is a second-generation (or later generation) star called a population 1 star
The stuff that makes up our solar system is the debris of a supernova
Stellar Remnants
After a supernova blows away most of a star’s mass, there is always something left
What is left then evolves in 3 possible ways:
If the stellar remnant has a mass of 1.4 times the mass of Sol or less, it will evolve into a white dwarf.
The original star would have a mass of less than 10 times the mass of Sol
If the stellar remnant has a mass between 1.4 and 2,5 times the mass of the Sun, it will evolve into a neutron star.
The original star would generally be between 10 and 29 times the mass of Sol
If the stellar remnant has a mass greater than 2.5 times the mass of Sol, it may evolve into a black hole
The original star would have a mass of more than 29 times the mass of Sol.
This is highly simplified; the composition of the star, the presence of binary partners or the rotation rate of the star might affect this, resulting in a neutron star instead of a black hole
Neutron Stars
In a neutron star, the mass of the star compresses the core so much that even the electron degeneracy can't support the huge gravitational compression
When this happens, the electrons are forced to combine with the protons in the nulceus
The result is a star made only of neutrons that has the same density as the nucleus of an atom
The density would be as high as 6x10¹⁷ kg/m³
This would mean that one teaspoon would have a mass of 6 billion tonnes
Black Holes
A black hole is so massive that even the neutrons are compressed together, such that there is no force which can support the star against gravity
The star collapses until it has no size. The matter collapses into a point called a singularity
Surrounding this point is something called the event horizon.
At the event horizon or inside, even light cannot escape the gravity og the black hole
Math of the Expanding Universe
Light coming from distant galaxies is the visible lightwaves you would be able to see with your eyes, which gets stretched into longer wavelengths and shifts from visible light to infrared light.
Scientists call this redshift, and the farther away the object, the more redshift it undergoes
Calculating Redshift
z = redshift
z = (wavelength₀ - wavelengthᵣ)wavelengthᵣ
Wavelength₀ = the observed wavelength of that spectral element
Wavelengthᵣ = The known wavelength of an element at rest
10Å = 1nm
Calculating Velocity
(wavelength₀ - wavelengthᵣ)wavelengthᵣ = vc
c = the speed of light in a vacuum
The speed of light in a vacuum is 3 x 10⁸ m/sec
v = velocity
Calculating Distance
v = H₀ x d
H₀ = the Hubble constant
The Hubble constant is approximately 20/km/sec/mps
mps is megaparsecs
A parsec is a unit of distance equal to approximately 3.26 light-years, and a megaparsec is equal to one million parsecs
d = distance from Earth