My dad, who is nearly 81 years old, is really into spacestuff. He loves to think about space, but many of the concepts and science are beyond his grasp. So after talking to him on the phone for an hour about these things, as we sometimes do, I thought it would be fun to write a basic introduction to the cosmos for him.
I’ve stolen images from all over the internet and I apologize for not having any attribution, I only later thought of publishing this post. If any copyright owners take issue with me using these images, please contact me and I’ll remove them.
Introduction
Let me take you on a journey through our cosmic neighborhood. We’ll start close to home, then explore the stars nearby, before zooming out to see our galaxy, clusters of galaxies, and beyond. Each step will take us further out, showing us more of the universe.
I’ve kept the explanations simple and included images to help you better understand.
I hope you enjoy reading this, and if you have any questions, feel free to ask.
Into the Cosmos!
In Our Backyard
The Sun is 151.5 million kilometers away from us. That’s really far, even though it’s just in our “backyard” in cosmic terms.
Light travels super fast—at almost 300,000 kilometers per second, which is about 1 billion kilometers per hour. That’s incredibly fast, faster than even the fastest German car!
In space, distances are so huge that we measure them using the speed of light. We use something called a “light-year,” which is the distance light can travel in one year—about 9.5 trillion kilometers (that’s 12 zeros!).
Sunlight takes about 8 minutes and 20 seconds to reach Earth, which is a little more than 8 light minutes.
Here’s an image showing the Sun and Earth to scale. The Earth is that tiny dot in the middle, and our Moon is a speck to the right.
The size of the Earth and Moon compared to the sun
A Side Note – The Sun’s End
The Sun gets its energy from burning hydrogen, but this fuel won’t last forever. When it runs out, the Sun will start to die. But don’t worry—this won’t happen for another 5 billion years!
When the Sun’s hydrogen is used up, it will start to grow bigger. It will become so large that it will swallow the closest planets, including Mercury, Venus, and even Earth.
As the Sun grows, it will turn into a “red giant.” After that, it will lose much of its outer layers and shrink down into a “white dwarf.” White dwarfs are still hot, but not as hot as the Sun is now.
In the end, the Sun will fade away and become a “black dwarf,” a star that no longer shines or gives off heat. However, this is just a theory—scientists aren’t entirely sure about this final stage.
The Neighbors
The nearest star to us, other than the Sun, is called Proxima Centauri. It’s 4.2 light-years away, which is extremely far—about 4 times 9.5 trillion kilometers.
Here’s a picture of Proxima Centauri taken by the Hubble Space Telescope:
Proxima Centauri
Since 2022, we’ve known that Proxima Centauri has two planets, and maybe even three. One of these planets is about the same size as Earth and is in a zone where life could possibly exist. It’s an exciting possibility!
Studies of quakes detected from the planet’s surface found liquid water in the planet’s rocky outer crust.
The District
Our Sun and Proxima Centauri are both part of the Milky Way, which is our galaxy. The Milky Way has between 200 to 400 billion stars, making it an average-sized galaxy.
Scientists believe that nearly every star in the galaxy has at least one planet orbiting it.
Here’s an artist’s impression of the Milky Way, as we can’t take a photo of the entire galaxy because we’re inside it. The red arrow shows where our Sun is located. The rest of the light in the image comes from the billions of other stars in the galaxy.
The position of the Sun in the Milky Way
The Milky Way is 100,000 light-years across. When you see the Milky Way in the night sky, you’re looking at the side view of the galaxy’s spiral. Here’s a photo I took of the Milky Way from Zeeland, showing a bright band of stars stretching across the sky:
A photo I took of the Milky Way in Zeeland, The Netherlands
The City
The average distance between galaxies is about 1 million light-years, which is extremely far! The closest galaxy to us is called Andromeda, and it’s 2.5 million light-years away.
Here’s a photo of the Andromeda Galaxy:
A photo of the Andromeda galaxy
The Province
The Milky Way and Andromeda are part of a group of galaxies called the Local Group.
In this image, you can see what a group of galaxies looks like—each spot of light is a whole galaxy, not just a star:
A cluster of galaxies
The Local Group is 10 million light-years across, and we’ve identified about 80 galaxies in it so far, though there are likely many more.
The Country, Continent, and Planet
Now things get really big! The Local Group is part of a much larger collection of galaxies called the Virgo Supercluster, which contains about 1,500 galaxies and is 110 million light-years across.
But it doesn’t stop there—the Virgo Supercluster is itself part of an even bigger structure called the Laniakea Supercluster, which contains around 100,000 galaxies and spans 500 million light-years.
In this image (created by a computer), you can see the shape of Laniakea, with the Milky Way (and Earth) marked by a red dot:
A computersimulation of the shape of the Laniakea supercluster with the Milky Way galaxy
Laniakea is also just one part of an even larger group of superclusters.
Here’s a map showing superclusters in the nearby universe, with Laniakea highlighted in yellow, between the red arrows:
A cluster of superclusters with Laniakea in the middle
The universe
The universe is unimaginably vast, so vast, that the metaphor for it in our story is the universe itself. It is estimated to be 93 billion light-years in diameter. Scientists estimate there are between 200 billion and 2 trillion galaxies in the observable universe.
Artist’s logarithmic scale conception of the observable universe with the Solar System at the center, inner and outer planets, Kuiper belt, Oort cloud, Alpha Centauri, Perseus Arm, Milky Way galaxy, Andromeda galaxy, nearby galaxies, Cosmic Web, Cosmic microwave radiation and Big Bang’s invisible plasma on the edge. Image by Unmismoobjetivo – CC BY-SA 3.0
Birthday calendar
The universe is between 13.8 and 26.7 billion years old, though we’re not completely sure.
The Sun is about 4.6 billion years old, and Earth formed soon after that. Our planet is estimated to be 4.54 billion years old.
To celebrate all these birthdays, here’s a treat, the awesome 1977 video “Powers of Ten”, explaining the scale of all the things: