Earth is a small rocky planet orbiting a very small Sun, which is nested within one of at least 100 billion galaxies.
Technology is allowing humans to see further than ever before but to date we still know so little even about Earth’s closest neighbors.
The sky above
The sky above the Northern Hemisphere alone contains at least 3,000 galaxies and over 100 million stars. With just the naked eye, we can only see 2 of these galaxies and around 4,000 stars.
Planet Earth only has 1 moon, unusual for our Solar System. The fifth largest moon in the Solar System, it was formed 4.5 billion years ago, shortly after the formation of Earth. The Moon orbits just under 240,000 miles away from Earth.
The closest planet to Earth can vary; sometimes it’s Venus and sometimes it’s Mars. These 2 terrestrial planets can often be seen in the night sky with the naked eye. On clear days, you can see Venus during the day due to its brightness.
For thousands of years humans have imagined pictures in the stars, including animals like bears and dogs. A group of stars forming a constant pattern is called a constellation. In reality these stars could be millions of miles apart.
Nicknamed the Red Planet, Mars is the closest rocky planet to Earth and home to the Solar System’s tallest mountain. Its proximity as well as its rocky surface make it an ideal candidate for potential human exploration.
Mars is located just under 140 million miles away from Earth. Light coming from Mars would take around 3 minutes to travel and reach Earth. Spacecraft traveling from Earth to Mars spend 9 months in the journey.
With 10% of the Earth’s mass, Mars is around half the diameter of Earth. However, it has the same amount of dry land as Earth because two–thirds of the surface of Earth is covered in water.
Mars Rovers exploration vehicles were designed and launched by the United States. They move around the surface of Mars and use a number of different on–board tools to perform various scientific experiments. Currently 3 rovers are on Mars, however only 2 are operational.
The surface of Mars is composed of a variety of rocks along with oxidized iron dust. Scientists have been hoping to find evidence of rocks formed by water but no conclusive evidence has been found as yet.
The nearest star system, or solar system to ours is called Alpha Centauri. It consists of 3 suns: Alpha Centauri A with Alpha Centauri B forming a binary pair and Proxima Centauri. The system can be viewed year–round in most of the Southern Hemisphere.
The word “close” is very misleading. Although this is our next nearest solar system, it’s still over 4 light years away. This equals to over 25 trillion miles. It takes 4 Earth years for light from the Alpha Centauri system to reach Earth.
Alpha Centauri A and B orbit each other to form a binary pair. The distance between them is similar to the distance between our Sun and Uranus. Both Alpha Centauri A and B are about the same size as our Sun.
Proxima Centauri is the closest sun outside our Solar System. It’s also a very small sun, just a little larger than Jupiter. Some debate still exists over whether Proxima Centauri is actually part of the Alpha Centauri system or is passing through the system.
Astronomers believe they have detected the presence of planets orbiting Proxima Centauri in particular. One planet called Proxima b appears to be a rocky planet a bit larger than Earth. It orbits in what is thought to be a possible habitable zone for life.
Earth and our Solar System lie within a spiral galaxy called the Milky Way. The next big galaxy across from the Milky Way is also a spiral galaxy, called Andromeda. The Andromeda Galaxy with its bigger volume contains about twice the number of stars as the Milky Way.
Andromeda is 2.5 million light years from Earth. It takes 2.5 million years for the light from this galaxy to reach our atmosphere. The Andromeda Galaxy is the furthest object in the universe you can see with the naked eye.
The Andromeda Galaxy contains at least 1 trillion stars, making it larger than our own Milky Way. Astronomers believe that Andromeda was formed from the collision and merger of 2 smaller galaxies 5–9 billion years ago.
With the help of X-ray telescopes, astronomers have discovered a number of black holes located within the Andromeda Galaxy. After identifying 26 possible black holes, they determined at least one was a supermassive black hole.
The Andromeda Galaxy and the Milky Way will collide into each other in approximately 4 billion years. This collision is predicted to form a giant elliptical galaxy. Despite containing billions of stars each, the massive distance between each star means that direct star collision is improbable.
Segue 1, a dwarf galaxy, was discovered in 2006. This tiny galaxy orbits around our own larger galaxy, the Milky Way. Mostly made up of dark matter, Segue 1 contains only about 1,000 stars compared to 400 billion stars in the Milky Way.
Although Segue 1 is found quite close to the Milky Way, it takes 75,000 years for its faint light to reach Earth. Astronomers estimate that it orbits the Milky Way once every 600 million years.
Segue 1 only has the luminosity of 300 of our Suns, very dull in the scope of the universe. Telescopic technology first discovered this galaxy in 2006 because it's just too small and too faint to have been detected earlier.
Inside Segue 1
Segue 1 seems to contain ancient stars, possibly dating back to when the universe came into existence. This is evidenced by the apparent low metal content of its stars. Metal didn’t appear in the universe until a few generations of stars went into supernova.
Betelgeuse is a rare type of star called a red supergiant. Its size changes and it can be 700–1,000 times bigger than our Sun. Seen all over the world, it forms part of the constellation known as Orion, the hunter. Betelgeuse is the tenth brightest star in the sky.
Betelgeuse is found relatively close to our Solar System. Located 640 light years from Earth, this red supergiant rotates very slowly, about 5 kilometers per second. This is due to the star losing mass as it burns fuel.
Betelgeuse is quite a young star, around 10 million years old. However, due to its enormous mass, scientists estimate that sometime in the next million years Betelgeuse will run out of resources and explode into a supernova.
If Betelgeuse took the place of our Sun it would reach all the way past the asteroid belt, devouring Mercury, Venus, Earth, Mars, and possibly even Jupiter. It’s approximately 700 times larger than our Sun.
When Betelgeuse runs out of fuel, its core will collapse in less than a second, exploding into a supernova. While the explosion will seem as bright as the full moon and may be visible during the day, Betelgeuse is too far away to damage Earth.