Universe by Otteri selvakumar (uplifting book club books TXT) 📕

Space is awesome. And complex. And frankly, there’s a whole lot we still don’t know about it. Scientists are constantly posing questions, putting forward mind- boggling new theories and discovering amazing new things about space. So we’ve put together a little primer on space and what scientists are saying about how it works. Enjoy. And remember, this is just a cheat sheet and we’re talking about complicated stuff. If something piques your interest, we’ve provided some links to learn more.

If we’re going to condense something, it’s best to know what we’re condensing. So, what is the universe? In short, pretty much everything. It includes the entire space-time continuum: all matter, energy, planets, stars and galaxies. The observable universe is an estimated 93 billion light-years in diameter. And that’s just the observable universe. So, you know, big.

"When I look up at the night sky and I know that yes we are a part of this universe, we are in this universe, but perhaps more important than both of those facts is that the universe is in us...Many people feel small cause they're small and the universe is big, but I feel big because my atoms came from those stars. There's a level of connectivity."

According to the Big Bang Theory, the universe as we know it started about 14 billion years ago. One moment the universe existed in a little point. And the next: boom. At a temperature of 10 billion degrees Fahrenheit, there was no matter, only energy. At first this nascent universe was totally opaque. After a while, though, as things began to cool, fundamental particles such as quarks and neutrinos began to condense from the energy into matter. Eventually, as the universe expanded and cooled, protons, neutrons and electrons formed from the more fundamental particles. Free electrons and protons created neutral hydrogen atoms, which allowed light to shine through. And as those elements started to cool, the universe as we know it began to develop.

How in the world do we know this, not having been hanging around in space 14 billion years ago? Well, we used to think the universe was fairly static, but in 1929 Edwin Hubble discovered that the universe is

actually expanding at a rapid rate. Everything is moving away from a single point. From that discovery, scientists have used mathematical models they can run backward in time to theorize that the entire universe came from a single point - the BIG BANG. Of course, now we want to know what came before the bang...

Earth: The Blue Planet

When we think of the universe, we usually think of what’s “out there,” but our very own planet Earth is a part of the universe, too. And what better vantage point to look at the universe than right where we’re standing.

Earth, the third planet from the sun, was formed 4.54 billion years ago, and has achieved the great distinction of hosting life—which requires just the right combination of temperature, atmosphere and water. As scientists look for other potential life in the universe, they concentrate their searches on planets that are in the "goldilocks zone" - the right distance from their star to support liquid water, which we assume is required for life - as we know it at least. For stars that are the same brightness as our sun, that means a distance of approximately 150,000,000 km (93 million miles) , give or take a few million. For smaller, colder stars, planets must be closer, and for hotter stars, farther away.

The Earth rotates every 24 hours, which gives us our days, as we are brought around to face the sun each morning. The Earth also revolves around the sun in its year-long orbit. Because the Earth's axis is tilted, as it moves around the sun we experience different seasons as hemispheres lean toward or away from the Sun. 70% of the Earth’s surface is covered by oceans. The atmosphere is 78% nitrogen, 21% oxygen and 1% Argon and the rest other elements.

The planet weighs a whopping 6,000,000,000,000,000,000,000,000 (6 x 10^24) kilograms. Its nickel-iron core provides a powerful magnetic field, which in turn deflects solar winds that would harm life.

The Sun: Star Power

Sure, we all know how important stars are. Without our star the Sun, there wouldn’t be life on earth. But what exactly is a star?

Well, basically, it’s gas collapsing in on itself.

Most of the matter in the universe is made of hydrogen (75%) and helium (23%), which hang around in the form of clouds of molecular gas - some of "primordial", meaning it is left over from the Big Bang. When a disturbance such as a shock wave from a nearby exploding supernova causes a gas cloud to collapse, that’s when a star begins to form. This collapse causes the gas to heat up (and heat up and heat up to 10 million K) until it turns to plasma - a form of matter where electrons have been stripped from atoms and the nuclei are barely holding together. Finally, with the heat and pressure hydrogen nuclei combine to form a helium nucleus—this is called nuclear fusion. It’s this fusion that defines a star. But

that process doesn’t happen overnight. It takes about 10,000,000 years for the cool interstellar gas to become a star.

Stars come in a variety of sizes and colors. The cooler stars give off a reddish color while the warmer ones give off a bluish color. This may seem counterintuitive, but think about the lights on your house. Regular old orange-looking tungsten bulbs burn at about 2800 K while blue looking fluorescent bulbs burn at around 5600 K (much hotter). And the light from the sun outside? That’s around 7000 K here on earth.

Smaller red stars called red dwarfs use less energy but burn much longer (up to 10 trillion years). The biggest stars that use the most energy, the blue supergiants, die out much faster (in only a few million years).

Our star, the sun, is a yellow dwarf because its radiation is strongest in the yellow-green spectrum.

Although not particularly large as far as stars go (with a diameter of approximately 1,392,684 km), it is thought to be brighter than 85% of the stars in the universe. The sun is middle aged - it has about 5 billion years to go.

Our Solar System

Our solar system is made up of the sun and everything that orbits it—that includes eight planets, several dwarf planets (poor Pluto), the asteroid belt (between Mars and Jupiter) and lots of small solar system bodies such as comets.

The four planets closest to the Sun—Mercury, Venus, Earth and Mars—are known as terrestrial planets because their surfaces are solid and composed of rock and metal. The four outer planets are the gas giants: Jupiter, Saturn, Uranus and Neptune. The first two gas giants are made up of mostly hydrogen and helium while the outermost planets are composed of mostly of water, ammonia and methane. Pluto, which used to be known as the ninth planet, was downgraded to a “dwarf planet” in 2006.

Galaxies Near and Far, Far Away

Galaxies are huge clusters of gas, particles and stars. We aren’t certain how many are out there, but in just the observable universe, scientists believe there are about 100 billion. And in each of these galaxies are billions of stars and accompanying solar systems.

There are three shapes of galaxies: spiral, elliptical and irregular.

Spiral Galaxies

Our very own Milky Way is a spiral galaxy. It’s shaped like a flat disk with spiraling arms and a more bulbous center, where many of the oldest stars reside. All of the dust, stars and planets revolve around this center, which exudes the gravitational force that keeps that galaxy together. Spiral galaxies spin around their center at hundreds of kilometers per second.

Elliptical Galaxies

These roundish galaxies are sometimes nearly circular or can be more elongated. These galaxies do have a center, but their stars tend to move more randomly than in spiral galaxies.

Irregular Galaxies

Lots of galaxies are not spiral or elliptical. Instead, they take on irregular patterns, often due to gravitational influences of other nearby galaxies. These funky galaxies are called irregular galaxies.

Our Beautiful Milky Way

The planet Earth resides in the Milky Way galaxy, a spiral-shaped galaxy with more than 100 billion stars. It’s called the Milky Way because of the milky appearance that the thickest band of stars has when you look up in the sky from planet Earth. What that milky-looking stuff is is the center of our galaxy. And in the very center of the center of our galaxy, there is a supermassive black hole called Sagitarrius A.

Our sun and solar system is in the Orion Arm of the Milky Way’s spiral, about two-thirds of the way, or 26,000 light-years, from the center of the galaxy. The nearest neighboring spiral galaxy is Andromeda, which is actually moving toward the Milky Way at about 110 kilometers per second. But don’t worry, the collision isn’t likely to happen for another four billion years.

Binary Stars and Multiple Star Systems

When we look up in the night sky and see a star, chances are we’re actually seeing not a single star, but two or even more stars. More than four-fifths of all stars are either binary stars—which orbit each other —or several stars that orbit each other, creating a multiple-star system.

With binary stars, the larger of the two stars is considered to be the primary star. These two stars can have wide or close orbits. Those with wide orbits have little effect on one another, while those with close orbits can actually feed on each other (consuming material from their companion) and exude gravitational force on each other. In some cases, the larger of the two stars can pull the smaller one in completely.

Black Holes Big and Small

We can’t actually see black holes. Their gravitational force is so strong that it pulls in light and won’t let it escape. So how do we know black holes exist? Scientists observe the areas around black holes. By watching planets and stars that surround these