Astronomy Notes
Astronomy notes#
These are combined notes from the previous astronomy articles.
Big Bang#
Before 1929, many believed the universe was static and eternal. In 1929, Edwin Hubble discovered that galaxies are not static but are moving away from Earth at incredible speeds. This was the first evidence of the Big Bang.
Hubble’s law is the observation that galaxies are moving away from Earth at speeds proportional to their distance. The idea is that everything started from a single point.
13.7 billion years is one estimate for the age of the universe.
Gravity was defined at the moment of the Big Bang. With too little gravity there would be no collisions and no galaxies. With too much gravity everything would collapse into black holes.
The universe was created from nothing, or empty space, expanding faster than the speed of light. Empty space itself can expand faster than the speed of light.
The universe is cooling.
Energy converted into matter: E = mc^2.
A nuclear explosion converts a small amount of matter into a huge amount of energy.
When the universe was created, the opposite happened.
About 380,000 years after the Big Bang the universe started to become transparent. Before that it was opaque. Atoms gained their electrons.
Galaxies#
A light year is the distance light travels in a year, about 9.5 trillion kilometres.
Earth is about 25,000 light years away from the centre of the galaxy. The Milky Way is about 100,000 light years across. Andromeda, our closest large galactic neighbour, is about 200,000 light years across.
Gravity makes stars. The first stars formed about 200 million years after the Big Bang. Then gravity pulled them together, forming galaxies.
The Hubble Space Telescope can see early galaxies formed roughly 1 billion years after the formation of the universe.
Supermassive black holes are at the centre of many galaxies. A quasar forms when a black hole consumes matter quickly and discharges energy back into space.
In astronomy, an aeon is defined as a billion years.
In Buddhism, an aeon or mahakalpa is often said to be 1,334,240,000 years, the life cycle of the world.
Dark matter is thought to help hold galaxies together. In computer simulations, visible matter alone did not create enough gravity to keep a galaxy together. Adding virtual dark matter helped the galaxy hold together.
Stars#
Stars form from nebulas, which are nurseries of dust and gas. They form with hydrogen, gravity and time. Gravity compresses material until there is enough heat for nuclear fusion.
Gravity compresses the outer layers of the star while fusion pushes outward. It is like a controlled explosion.
Light travels at 1080 million kilometres an hour. A beam of light could go around the Earth 7 times in 1 second.
Most stars are so far away that their light can take years to reach us.
When fusion weakens, gravity closes in and the star expands into a red giant. The hydrogen burns up and the star starts using helium, which fuses into carbon. The star disintegrates, leaving a core called a white dwarf. The fusion process has stopped.
With larger stars, the iron core can blow up as a supernova. The iron on Earth may be from a dead star.
Material from deep inside a star’s core forms heavier elements such as gold, silver and platinum. There is little time for those elements to form, which is why they are rare.
The Sun#
The sun is about 148,800,000 kilometres away. It is about 1 million times bigger than Earth by volume and about 1 million kilometres in diameter. It is about 5 billion years old.
Light from the sun takes about 8 minutes to reach Earth. Photons can take thousands of years to get from the core of the sun to the surface due to collisions.
Solar storms can damage Earth infrastructure and communication satellites. Solar magnetic fields can die out as solar flares, or erupt and send radiation that can reach us in minutes.
The sun’s magnetic field is pulled by the solar wind, creating a heliosphere that shields us from harmful galactic cosmic rays.
Most solar systems have 2 stars. We are lucky to have a single sun. The sun is a relatively small star.
The sun has about 5 billion more years of stable life.
Other stars#
- Bellatrix: about 250 light years away, 6 times bigger than the sun and 4000 times brighter, but it will die young
- EV Lacertae: about 16 light years away, smaller than the sun, spins faster and has a much stronger magnetic field
- Eta Carinae: 5 million times larger than the sun
- Betelgeuse: much larger than Eta Carinae
- VY Canis Majoris: around 1 billion times bigger than the sun
Black holes#
Light cannot be emitted from a black hole. Matter falls into an infinitely deep hole.
As you pass into the black hole you reach the speed of light. After that we do not know.
Black holes were once theoretical, a prediction from Einstein’s work.
Sagittarius A* is the closest known supermassive black hole, about 4 million times more massive than the sun and about 26,000 light years from Earth.
Black holes are formed by the death of a massive star. Very large stars collapse and the core keeps collapsing into a very small space. A black hole is born.
Supermassive black holes gather more and more matter. Friction builds up and the disc starts to glow. The brighter the disc, the bigger the black hole.
Quasars are intense light and energy, outshining entire galaxies. When too much matter collides violently, huge amounts of energy create some of the brightest light in the universe.
Our galaxy is the Milky Way. In about 4 billion years it will merge with the Andromeda galaxy.
Einstein theorised that near a black hole, time would slow down due to relativity. People going through an event horizon would not notice time being stretched.
Asteroids#
The Chicxulub crater is linked to the extinction event that killed the dinosaurs and many other species on Earth. It is proposed to have come from a low angle, sending superheated dust and rock into the atmosphere and blocking out the sun for a year.
There are roughly 500,000 asteroids in the main asteroid belt.
The dust cloud that formed the sun also caused many collisions. Material stuck together and formed the solar system.
Jupiter’s mass creates a large gravitational force that pulls on many objects, including asteroids. It limited the formation of other planets and influenced where the asteroid belt formed.
Cosmos notes#
Cosmos is the Greek word for the order of the universe, the opposite of chaos.
Orion Nebula#
- 1500 light years from Earth
- Orion’s Belt
- The middle star in Orion’s sword is a stellar nursery, a place where stars are born
Our solar neighbourhood#
- Neptune and Triton are about 4 light hours from Earth
- Mars has Olympus Mons, the largest volcano on Mars, about 22 kilometres high
- There are around 100 billion galaxies
Earth and Eratosthenes#
The size of Earth was discovered by Eratosthenes.
In Alexandria, precisely at noon, the sun shone directly down into a well. Eratosthenes experimented to see if, 800 kilometres away in Syene, a stick cast a shadow when there was no shadow in Alexandria.
The only answer was that Earth is curved. The sun is so far away that its rays are effectively parallel.
He worked out the angle from the difference in shadow. 7 degrees is about 1/51.42 of 360 degrees. He hired a man to pace out the distance from Alexandria to Syene, about 800 kilometres.
51.42 * 800 = 41,142 km, which was his estimate for the circumference of Earth.
Library of Alexandria#
The Library of Alexandria had around 1 million scrolls at its peak.
Important figures connected to the tradition around Alexandria:
- Eratosthenes
- Hipparchus: mapped constellations and established brightness of stars
- Euclid: systematised geometry
- Dionysius Thrax: defined the parts of speech
- Herophilos: physiologist who argued for the brain instead of the heart
- Archimedes: great mechanical genius
- Ptolemy: compiled the Earth-centred model that held sway for 1500 years
- Hypatia: mathematician and philosopher
- Aristarchus: heliocentric view of the sun as the centre
Plato and the Pythagoreans suppressed Ionian thinking. They pushed their own agenda because they were comfortable in a slave economy.
The total number of stars in the cosmos is larger than all the grains of sand on all the beaches in the world.
You cannot look at light from space without travelling back in time.
From Earth to the centre of the Milky Way galaxy is about 30,000 light years. The next spiral galaxy away from ours is about 2 million light years away.
Relativity#
Special theory of relativity rules:
- Light travels at the same speed whether the observer is moving or stationary
- Nothing can travel faster than the speed of light
- The speed of light is constant, about 300,000 kilometres a second
The human brain#
- The right hemisphere: pattern recognition, creative insight and sensitivity
- The left hemisphere: rational, analytic and critical thinking
The right generates ideas, the left tests their validity.
Do not trust, verify.
Aggression, child rearing, sex and willingness to follow leaders blindly are associated with lower parts of the brain. Reading, speaking and writing are associated with the cerebral cortex.
We have to figure out much more than the genes know. The brain changes quickly through learning. We are not trapped in behavioural patterns from genes.
We are responsible for what is put into our brains. We are not at the mercy of the reptile brain. We can change ourselves.
Then we needed more than our brains. We stored more inside libraries and, later, the internet.
There are many books we can read, but there are millions of options.
The trick is to know which books to read.
The printing press appeared in China in the 12th century. Printing books in Europe took longer.