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10 Dec 2025
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Comprehensive Physics Notes for Nat5 Cosmology Unit
Sophieeee ๐๐๐๐บ๐
@sophiesnotes
1 / 5
Cosmic Definitions
Ever wondered what makes our cosmic neighbourhood tick? Let's break down the key players in space, from the smallest moons to the entire universe itself.
A star is essentially a massive hot ball undergoing nuclear fusion - like our Sun, which powers our entire solar system. Planets are spherical bodies made of rock or gas that orbit these stars, whilst moons are smaller chunks of matter that orbit planets instead.
Our solar system includes the Sun plus everything orbiting it - the eight planets, their moons, and loads of other space debris. Scale this up massively, and you get a galaxy - a huge cluster of stars, many with their own planetary systems. The universe contains countless galaxies separated by mostly empty space.
Exoplanets are planets outside our solar system, and scientists are constantly hunting for ones that might support human life. They need similar atmospheres to Earth, plus the potential for shelter, sustainable food sources, and liquid water.
Key insight: Each cosmic structure builds up to the next - moons orbit planets, planets orbit stars, stars cluster in galaxies, and galaxies make up the universe.
Light Years
Here's something that trips up loads of students: a light year measures distance, not time! It's simply how far light travels in one whole year.
Since light zips along at 3 ร 10โธ m/s, we can calculate this distance using d = vt. One year equals 31,536,000 seconds (365 ร 24 ร 60 ร 60), so light travels 9.46 ร 10ยนโต metres in a year.
Why does this matter? Space distances are absolutely massive - saying the Crab Nebula is 6,500 light years away is much easier than writing out 6.15 ร 10ยนโน metres! When astronomers measure these cosmic distances, they're essentially looking back in time, since the light has taken years to reach us.
Quick tip: Always convert years to seconds first (multiply by 365 ร 24 ร 60 ร 60), then use d = vt with light speed.
The Big Bang Theory
Imagine the entire universe squeezed into something thousands of times smaller than a pinhead - that's how astronomers believe everything started 14 billion years ago in the Big Bang.
This wasn't an explosion but rather rapid expansion of space itself. Within seconds, the universe grew from smaller than an atom to bigger than a galaxy! Protons and neutrons formed after just one second, whilst hydrogen and helium nuclei appeared after three minutes when temperatures dropped below 1 billionยฐC.
After 300,000 years, things cooled enough (around 3,000ยฐC) for atoms to form properly. The universe filled with hydrogen and helium gas clouds, which eventually became the galaxies and solar systems we see today.
Scientists back this theory with solid evidence: galaxies moving away from us, cosmic microwave background radiation (leftover heat from the Big Bang), and the abundance of light elements like hydrogen and helium throughout space.
Remember: The Big Bang wasn't an explosion in space - it was space itself expanding rapidly from an incredibly dense point.
The Electromagnetic Spectrum
Astronomers don't just use visible light to study space - they've got an entire toolkit of electromagnetic radiation that all travels at light speed .
The electromagnetic spectrum includes seven types of radiation, from radio waves (longest wavelength, lowest frequency) through to gamma rays (shortest wavelength, highest frequency). Each type needs different detectors and reveals different cosmic secrets.
Radio waves use aerials to study planetary distances, whilst microwaves detected through diode probes revealed cosmic background radiation from the Big Bang. Infrared radiation shows up on blackened thermometers and spots objects just outside visible light, perfect for studying cooler cosmic bodies.
Visible light still uses photographic film and tells us about star temperatures and sizes. Ultraviolet radiation, detected with fluorescent paint, helps study young star formation. X-rays and gamma rays both use photographic film and Geiger counters respectively to detect extreme cosmic events like black holes and supernovae.
Key fact: Different wavelengths reveal different cosmic phenomena - longer waves for cooler objects, shorter waves for the most energetic events.
Spectroscopy - Continuous and Line Spectra
Want to know what distant stars are made of? Spectroscopy is your answer - it's like cosmic fingerprinting that reveals the chemical composition of stars billions of miles away.
A spectroscope splits starlight into either continuous or line spectra. Continuous spectra come from solids, liquids, and high-pressure gases at high temperatures - they show all colours blending smoothly together, each with different frequencies and wavelengths.
Line spectra are far more exciting for astronomers. They're produced by hot gases at low pressure or gases with electric currents passing through them. Instead of continuous colour, you get distinct lines at specific frequencies and wavelengths.
Here's the brilliant bit: every chemical element has its own unique line spectrum pattern. This means astronomers can identify exactly which elements are present in distant stars just by analysing the light they emit - it's like having a cosmic chemistry lab!
Amazing fact: We can determine what distant stars are made of more accurately than we can analyse some materials here on Earth, all thanks to spectroscopy.
We thought youโd never ask...
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Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
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This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
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The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
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In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
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very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
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I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
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THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because itโs too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
Comprehensive Physics Notes for Nat5 Cosmology Unit
Sophieeee ๐๐๐๐บ๐
@sophiesnotes
The universe is massive, ancient, and full of incredible structures - from tiny planets to enormous galaxies spanning billions of light years. Understanding cosmology helps us grasp our place in this vast cosmic neighbourhood and how everything from stars to... Show more
Cosmic Definitions
Ever wondered what makes our cosmic neighbourhood tick? Let's break down the key players in space, from the smallest moons to the entire universe itself.
A star is essentially a massive hot ball undergoing nuclear fusion - like our Sun, which powers our entire solar system. Planets are spherical bodies made of rock or gas that orbit these stars, whilst moons are smaller chunks of matter that orbit planets instead.
Our solar system includes the Sun plus everything orbiting it - the eight planets, their moons, and loads of other space debris. Scale this up massively, and you get a galaxy - a huge cluster of stars, many with their own planetary systems. The universe contains countless galaxies separated by mostly empty space.
Exoplanets are planets outside our solar system, and scientists are constantly hunting for ones that might support human life. They need similar atmospheres to Earth, plus the potential for shelter, sustainable food sources, and liquid water.
Key insight: Each cosmic structure builds up to the next - moons orbit planets, planets orbit stars, stars cluster in galaxies, and galaxies make up the universe.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
Light Years
Here's something that trips up loads of students: a light year measures distance, not time! It's simply how far light travels in one whole year.
Since light zips along at 3 ร 10โธ m/s, we can calculate this distance using d = vt. One year equals 31,536,000 seconds (365 ร 24 ร 60 ร 60), so light travels 9.46 ร 10ยนโต metres in a year.
Why does this matter? Space distances are absolutely massive - saying the Crab Nebula is 6,500 light years away is much easier than writing out 6.15 ร 10ยนโน metres! When astronomers measure these cosmic distances, they're essentially looking back in time, since the light has taken years to reach us.
Quick tip: Always convert years to seconds first (multiply by 365 ร 24 ร 60 ร 60), then use d = vt with light speed.
Sign up to see the contentIt's free!
Access to all documents
Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The Big Bang Theory
Imagine the entire universe squeezed into something thousands of times smaller than a pinhead - that's how astronomers believe everything started 14 billion years ago in the Big Bang.
This wasn't an explosion but rather rapid expansion of space itself. Within seconds, the universe grew from smaller than an atom to bigger than a galaxy! Protons and neutrons formed after just one second, whilst hydrogen and helium nuclei appeared after three minutes when temperatures dropped below 1 billionยฐC.
After 300,000 years, things cooled enough (around 3,000ยฐC) for atoms to form properly. The universe filled with hydrogen and helium gas clouds, which eventually became the galaxies and solar systems we see today.
Scientists back this theory with solid evidence: galaxies moving away from us, cosmic microwave background radiation (leftover heat from the Big Bang), and the abundance of light elements like hydrogen and helium throughout space.
Remember: The Big Bang wasn't an explosion in space - it was space itself expanding rapidly from an incredibly dense point.
Sign up to see the contentIt's free!
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Improve your grades
Join milions of students
By signing up you accept Terms of Service and Privacy Policy
The Electromagnetic Spectrum
Astronomers don't just use visible light to study space - they've got an entire toolkit of electromagnetic radiation that all travels at light speed .
The electromagnetic spectrum includes seven types of radiation, from radio waves (longest wavelength, lowest frequency) through to gamma rays (shortest wavelength, highest frequency). Each type needs different detectors and reveals different cosmic secrets.
Radio waves use aerials to study planetary distances, whilst microwaves detected through diode probes revealed cosmic background radiation from the Big Bang. Infrared radiation shows up on blackened thermometers and spots objects just outside visible light, perfect for studying cooler cosmic bodies.
Visible light still uses photographic film and tells us about star temperatures and sizes. Ultraviolet radiation, detected with fluorescent paint, helps study young star formation. X-rays and gamma rays both use photographic film and Geiger counters respectively to detect extreme cosmic events like black holes and supernovae.
Key fact: Different wavelengths reveal different cosmic phenomena - longer waves for cooler objects, shorter waves for the most energetic events.
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Improve your grades
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By signing up you accept Terms of Service and Privacy Policy
Spectroscopy - Continuous and Line Spectra
Want to know what distant stars are made of? Spectroscopy is your answer - it's like cosmic fingerprinting that reveals the chemical composition of stars billions of miles away.
A spectroscope splits starlight into either continuous or line spectra. Continuous spectra come from solids, liquids, and high-pressure gases at high temperatures - they show all colours blending smoothly together, each with different frequencies and wavelengths.
Line spectra are far more exciting for astronomers. They're produced by hot gases at low pressure or gases with electric currents passing through them. Instead of continuous colour, you get distinct lines at specific frequencies and wavelengths.
Here's the brilliant bit: every chemical element has its own unique line spectrum pattern. This means astronomers can identify exactly which elements are present in distant stars just by analysing the light they emit - it's like having a cosmic chemistry lab!
Amazing fact: We can determine what distant stars are made of more accurately than we can analyse some materials here on Earth, all thanks to spectroscopy.
We thought youโd never ask...
What is the Knowunity AI companion?
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
Where can I download the Knowunity app?
You can download the app from Google Play Store and Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help โ all at your fingertips.
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Most popular content in Physics
Most popular content
English - inspector calls quotes and analysis
Quotes from every main character
English Literature10
Can't find what you're looking for? Explore other subjects.
Students love us โ and so will you.
4.9/5
App Store
4.8/5
Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because itโs too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan S
iOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha Klich
Android user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
Anna
iOS user
Best app on earth! no words because itโs too good
Thomas R
iOS user
Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.
Basil
Android user
This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.
David K
iOS user
The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!
Sudenaz Ocak
Android user
In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.
Greenlight Bonnie
Android user
very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.
Rohan U
Android user
I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didnโt even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as Iโm sure you too will see developments.
Xander S
iOS user
THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH ๐๐๐ฒ๐ค๐โจ๐๐ฎ
Elisha
iOS user
This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now
Paul T
iOS user