Because gravity is very low in space, why do satellites orbiting the Earth not fall?

 Gravity in space isn't actually weak. If you built a 250-mile-high tower into low Earth orbit, you wouldn't float at the top—you'd still feel 90% of your normal weight.

This is the exact altitude where the International Space Station operates, firmly within Earth's gravitational grip.

The International Space Station orbits Earth at approximately 17,500 miles per hour, perpetually falling toward the planet but moving sideways fast enough to match its curvature. Source: Wikimedia Commons.

So why do astronauts float, and why do satellites not come crashing down? The answer is that they are actually falling. They are just moving sideways so incredibly fast that they keep missing the ground.

To understand how this works, imagine standing on a high mountain and throwing a baseball straight ahead. Gravity pulls the ball down, and it hits the dirt a few dozen feet away. If you throw it much faster, it travels further before landing.

Now imagine you have a cannon powerful enough to fire a cannonball horizontally at 17,500 miles per hour. As soon as the cannonball leaves the barrel, gravity begins pulling it downward. But because the Earth is round, the surface is curving away beneath it. At 17,500 miles per hour, the rate at which the cannonball falls downward perfectly matches the rate at which the Earth curves away.

The cannonball is in a constant state of free fall, but it never reaches the planet. This is exactly what an orbit is. Satellites are just projectiles fired sideways with enough velocity to ensure that as they drop toward Earth, the surface drops away at the exact same rate.

If a satellite in orbit suddenly stopped moving sideways, the illusion of zero gravity would instantly vanish. It would plummet straight down and burn up in the atmosphere, pulled by the exact same gravity that holds it in its orbital path.

What keeps the Sun floating in space?

 The Sun isn’t actually floating in space. Hurtling sideways at 514,000 mph, it is perpetually falling toward the center of the Milky Way—and constantly missing.

On Earth, humans intuitively think of "down" as a universal direction. If an object is dropped, it falls to the ground. But in the vacuum of space, there is no inherent up or down. Objects only fall when the gravity of a larger mass pulls them in.

Within the local cosmic neighborhood, the Sun is the dominant source of gravity. It contains 99.8% of all the mass in the entire solar system. Because it is so massive, there is nothing nearby strong enough to pull it in any specific direction. Instead of the Sun falling toward anything else, all the planets, asteroids, and comets are constantly falling toward it.

On a larger scale, however, the Sun's trajectory is driven by the gravity of the Milky Way. The solar system sits in the Orion Arm, about 26,000 light-years from the center. The galaxy contains hundreds of billions of stars, vast clouds of gas, a massive halo of dark matter, and a supermassive black hole. The immense combined mass of all this material exerts a tremendous gravitational pull on the Sun.

The reason the Sun doesn’t plunge straight into the galactic core is its incredible lateral speed. As the galaxy’s gravity pulls the Sun inward, its forward momentum carries it sideways. The two forces balance out perfectly into a stable orbit.

This is the exact same mechanical principle that keeps the Earth orbiting the Sun, and the Moon orbiting the Earth. It takes the Sun roughly 230 million years to complete a single trip around the Milky Way—a period known as a galactic year. Since its formation 4.6 billion years ago, the Sun has completed this massive orbit about 20 times.

A map of the Milky Way galaxy showing the Solar System on the Orion Arm. Photo by Andrew Z. Colvin is licensed under CC BY-SA 4.0.

What are some amazing space facts which left you bewildered?

 

• The oldest planet in the entire universe, PSR B1620-26 b (nicknamed "Methuselah")
  [1]

This is the oldest exoplanet found to date at 13 billion years old, possibly the oldest ever considering the Universe itself is only a little older at 13.7 billion years old! It was found deep inside the core of what is called a “globular cluster” of stars, which are composed of the very first stars that were formed right after the Big Bang. And based on our knowledge of planet formation planets are born soon after their parent star, so if the exoplanet’s star is really old, then the planet itself must be really old as well.

• Megamasers

To send 2016 off properly, Hubble has captured the most detailed image to date of the mysterious galaxy IRAS 16399-0937, which acts as a giant, astronomical laser.

But it's not your standard laser. Instead of blasting out visible light, the galaxy pumps out an intense and constant stream of microwave radiation. "This galaxy has a far more exciting and futuristic classification than most - it hosts a megamaser," explains NASA (microwave + laser = maser). Masers are found throughout the Universe, wherever molecular clouds of dust amplify any microwave radiation that passes through, enhancing and focussing the amount that's emitted on the other side.

There are even some masers in our own galaxy, but megamaser IRAS 16399-0937 is a lot brighter - 100 million times brighter, to be specific, and almost the entire galaxy acts as a maser, rather than just one or two molecular clouds.

• Hubble Telescope’s Last Day is not far

The Hubble’s estimated decay date would be somewhere between the year 2030 and 2040. So what happens after that ?

The James Webb Space Telescope 

[2]

, also called Webb or JWST, is a large, space-based observatory, optimized for infrared wavelengths, which will complement and extend the discoveries of the Hubble Space Telescope. It will cover longer wavelengths of light than Hubble and will have greatly improved sensitivity. It is under construction and scheduled to launch in October 2018.

Hubble, one of the highly advanced telescope was launched in the year 1990. Imagine the amount of technical advancements the new JWST would have and it’s impact on astronomical studies.

Can you blow my mind with a space fact?

 

1. Neutron stars can spin at a rate of 600 rotations per second.

2. Space is completely silent

3. There is an uncountable number of stars in the known universe

4. The Apollo astronauts' footprints on the moon will probably stay there for at least 100 million years

5. 99 percent of our solar system's mass is the sun

6. More energy from the sun hits Earth every hour than the planet uses in a year

7. If two pieces of the same type of metal touch in space, they will bond and be permanently stuck together

8. The largest asteroid in our solar system is a mammoth piece of space rock named Ceres

9. One day on Venus is longer than one year.

10. Jupiter's Red Spot is shrinking

11. One of Saturn's moons has a distinct two-tone coloration

12. Spacecraft have visited every planet

13. Number of active communicative extraterrestrial civilizations in the Milky Way galaxy.

What are the saddest truths about exploring outer space?

 This is Kepler-186f, the first planet discovered with a radius comparable to Earth's, located within another star's habitable zone.

However, Kepler-186f sits more than 550 light-years away from Earth, and a single light-year spans roughly 5.9 trillion miles. In other words, what we're currently observing of Kepler-186f actually represents how it appeared over 550 years in the past.

Discovering Kepler-186f confirms that Earth-like planets genuinely exist within habitable zones elsewhere. That said, given its distance exceeding 550 light-years, it remains too far for current telescopes, or even upcoming next-generation instruments, to gather further details (meaning the image above is essentially just artistic interpretation). No further specifics regarding its actual habitability have surfaced yet, and realistically, given current technological limits, we shouldn't expect meaningful breakthroughs anytime soon.

My childhood fascination with astronomy eventually shaped me into an agnostic atheist. While I don't personally believe in any deity, it genuinely feels like the universe remains, and will likely always remain, beyond the full grasp of Earth's intellectuals, seemingly destined to stay a permanent mystery to life here.

As a kid, I marveled at incredible discoveries made by countless scientists throughout history and the sheer brilliance of human intellect, yet simultaneously felt stunned by how utterly insignificant and brief human existence appears on a cosmic scale. Our sun, over a million times larger than the planet we inhabit, represents merely one among 300 billion stars within the Milky Way, itself just one galaxy among billions scattered throughout the universe. And multiverse theory proponents even suggest multiple universes might exist simultaneously.

Much like countless unresolved questions, how life originated on Earth, how consciousness actually functions, the true nature of time itself, philosophers and scientists have wrestled with understanding the universe for millennia; it remains so fundamentally and profoundly complex that full human comprehension may forever stay out of reach. Perhaps the universe was simply never meant to be entirely understood.

It's genuinely disheartening realizing humanity faces such hard, unavoidable limits, and nothing illustrates this reality more clearly than space exploration itself.

Which is the biggest mystery in space science?

 Blackhole.

Why?

• It can't be seen. Yes! a blackhole cannot be detected neither with a telescope nor by any spacecraft, yet it is found to exist.
• It doesnot emit radiation. Being the most massive objects of the Universe ( an object of infinite mass ), it doesn't emit it's own radiation rather it is detected by the radiation given off by the body which is in it's acreetion disk. On the contrary, every body in this universe that has mass is found to emit radiation. An 'atom' ( basic structural unit of everything around us ) also emits radiation.
• If you wish to remain forever young, you should prefer going into a Blackhole. It's​ gravitational pull is so massive that even light cannot escape it's surface, time inside the blackhole stops.

• Even you can become a black hole. Theoretically,any object compressed to very high density has the potential of becoming a Blackhole.
• Despite being so massive, they can evaporate with time.

• Don't be surprised when a 5 ft 7′ guy suddenly looks like a 6 ft 4′ ! A phenomenon called 'spagehttification' takes place as your feet tend to get more closer to the center of Blackhole.

P.S.: No one is able to ascertain firmly the reason for all these phenomenon. The concept of Blackhole though discovered over a 100 years ago, still remains a matter of debate to the leading scientists of the World.

How do stars survive in intergalactic space?

 Millions of "rogue" stars have been violently ejected into the empty voids between galaxies. They don't just survive in the dark—this absolute isolation is the safest place a star can be.

A star's existence has nothing to do with its galactic environment. It is simply a massive ball of gas held together by its own gravity, engaged in a constant tug-of-war with the outward pressure of nuclear fusion at its core. As long as a star has enough mass to maintain fusion, it is entirely self-sufficient. It does not rely on a host galaxy for fuel, warmth, or structural support.

Inside a galaxy, stars face several gravitational hazards. They can be disrupted by passing stellar neighbors, swallowed by central supermassive black holes, or caught in the blast wave of a nearby supernova. Out in the intergalactic void, a rogue star is entirely free from these threats, left to burn its fuel in total peace.

Stars are born inside the gas-rich nurseries of galaxies, but violent gravitational interactions can forcibly eject them. When two galaxies collide, the chaotic shifting of gravitational fields can fling millions of stars out into the void in long, trailing "tidal tails." Alternatively, in a process known as the Hills mechanism, a binary star system wandering too close to a galaxy's central supermassive black hole can be torn apart. One star is captured by the black hole, while the other is violently slung outward at millions of miles per hour—fast enough to break free of the galaxy's gravitational grip entirely.

Once ejected, an intergalactic star faces a long, solitary timeline. Because there are no heavy molecular clouds in intergalactic space, a rogue star's death will not trigger the birth of new stars. It will simply consume its internal hydrogen reserves over billions of years, eventually swelling into a red giant and quietly collapsing into a white dwarf, neutron star, or black hole in the dark.

The reconstructed orbits of 20 high-velocity stars that are escaping the Milky Way's gravitational pull into intergalactic space. Photo by ESA is licensed under CC BY-SA 3.0 igo.

Why is space holding planets?

 Space isn't actually holding the planets up at all. Earth is locked in a perpetual freefall, hurtling sideways at 67,000 mph just fast enough to constantly miss the Sun.

To understand why planets stay in place, you first have to discard the idea of "up" and "down." On Earth, if you drop a rock, it falls down. But in the wider universe, "down" does not exist as a universal direction. Down is simply the path toward the center of the nearest massive object. There is no cosmic floor for planets to fall onto.

Instead of falling down, planets are constantly falling around. In 1915, Albert Einstein revolutionized our understanding of gravity by proposing that space and time are woven together into a four-dimensional fabric called spacetime.

Imagine stretching a large trampoline tight and placing a heavy bowling ball in the center. The ball causes the fabric to sink, creating a deep funnel. This is what the Sun does to spacetime. If you take a marble—representing a planet like Earth—and roll it sideways along the rim of that funnel, it won't drop straight to the center. It will circle the bowling ball.

Earth's natural tendency is to travel in a straight line out into deep space, but the steep curve of the Sun's gravity well constantly bends that straight path into a circle. The precise balance of forward momentum and the inward pull of curved space results in a stable orbit.

Are there any objects in space that are smaller than stars but larger than planets, such as brown dwarfs?

 If you packed 70 times more mass into Jupiter, it wouldn't get any wider. It would become a brown dwarf—a "failed star" trapped in the cosmic middle ground between planets and true stars.

To understand what a brown dwarf is, it helps to look at the firm mass boundaries that define stars and planets:

• A star is an object massive enough that the crushing pressure and heat in its core ignite the sustained nuclear fusion of regular hydrogen (hydrogen-1). The absolute minimum mass required to do this is roughly 80 times the mass of Jupiter.
• A planet like Jupiter does not have enough mass to ignite any kind of nuclear fusion. It generates no internal fusion energy and simply cools down over time.

If an object forms with a mass between roughly 13 and 80 times that of Jupiter, it falls directly into this middle ground. Unlike true planets, brown dwarfs are massive enough that their core pressure ignites nuclear fusion—but only the fusion of deuterium, a heavy isotope of hydrogen. Because deuterium is scarce, a brown dwarf burns through its supply in a few million years, which is a blink of an eye in cosmic terms.

Once the fuel is gone, the fusion stops. For the rest of its long life, the brown dwarf glows faintly in the infrared spectrum from leftover heat, slowly fading and cooling until it turns pitch black.

This size paradox is one of the most unintuitive physical properties of brown dwarfs. Due to the quantum mechanics of electron degeneracy pressure, adding mass to a brown dwarf does not make it physically larger—it just makes it denser. Gravity pulls the extra mass inward so tightly that a heavy brown dwarf remains almost exactly the same diameter as Jupiter.

A size comparison showing a low-mass star, a brown dwarf, and Jupiter. Due to extreme density, a brown dwarf has roughly the same physical volume as Jupiter despite being up to 80 times more massive. Source: Wikimedia Commons.

For decades, these objects only existed in mathematical theories because they emit almost no visible light. Astronomers finally found undeniable proof in 1995 with the discovery of Gliese 229B. Spotted orbiting a red dwarf star, it glowed faintly in the infrared, and its atmosphere contained methane—a molecule that cannot survive the intense heat of a true star. At the very bottom of the brown dwarf temperature scale, astronomers have now even found Y-dwarfs, which have cooled down so much that their atmospheres match the temperatures of a warm summer day on Earth.

What are the implications of space and time having no beginning or end?

 If space and time have no beginning or end, they create a mind-bending paradox: the universe should already be dead, and an exact replica of your life will repeat endlessly.

The most immediate problem an eternal universe creates is thermodynamic. The Second Law of Thermodynamics dictates that entropy—disorder—always increases. In a closed system with a finite amount of usable energy, an infinite amount of time guarantees that the system reaches "heat death." All stars would burn out, all black holes would evaporate, and space would settle into a uniform, freezing radiation bath. If the universe is infinitely old, it should already be in this dead state.

To avoid this paradox, an eternal universe requires a physical mechanism for renewal. This points toward cyclic models, where the universe undergoes endless sequences of expansion and contraction, resetting the entropy clock with each "Big Bounce." Alternatively, theories like eternal inflation propose that our visible universe is just one finite bubble in a constantly expanding multiverse where new regions of space continuously spark into existence.

An infinitely old and large universe also invokes the Poincaré recurrence theorem. In a bounded region of space, there is a finite number of ways matter and energy can be arranged. If time stretches infinitely into the past and future, every possible configuration of quantum states must eventually occur, and reoccur an infinite number of times. Every variation of history plays out endlessly across the expanse.

This infinite timeline eliminates the necessity of a "First Cause." Cosmological arguments for a creator rely on the premise that a finite chain of events must have a starting point. An eternal universe exists as a brute fact, requiring no genesis because there was never a "before" to trigger it.

Webb’s First Deep Field shows thousands of galaxies, including some of the faintest objects ever observed in the infrared, hinting at the vast scale of the cosmos. Source: Wikimedia Commons.

What are some of the most amazing facts about space?

 

• 1. Neutron stars can spin at a rate of 600 rotations per second.

• ​
  
  Neutron stars are one of the possible evolutionary end-points of high mass stars. They're born in a core-collapse supernova star explosion and subsequently rotate extremely rapidly as a consequence of their physics. Neutron stars can rotate up to 60 times per second after born. Under special circumstances, this rate can increase to more than 600 times per second.
  Source: Swinburne University of Technology Centre for Astrophysics and Supercomputing
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 2. All of space is completely silent.

• ​
  
  Sound waves need a medium to travel through. Since there is no atmosphere in space, space will always be eerily silent.
  You may be asking how astronauts can talk to each other in space. Lucky for them, radio waves cantravel through space. No problem there, Houston.
  Source: Cornell University Department of Astronomy
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 3. There is an uncountable number of stars in the known universe.

• ​
  
  We basically have no idea how many stars there are in the universe. Right now we use our estimate of how many stars there are in our own galaxy, the Milky Way. We then multiply that number by the best guesstimate of the number of galaxies in the universe. After all that math, NASA can only confidently say that say there all zillions of uncountable stars. A zillion is any uncountable amount.
  An Australian National University study put their estimate at 70 sextillion. Put another way, that's 70,000 million million million. This figure is basically a guess, though.
  Sources: University of California at Santa Barbara ScienceLine,
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 4. The Apollo astronauts' footprints on the moon will probably stay there for at least 100 million years.

• ​
  
  Since the moon doesn't have an atmosphere, there's no wind or water to erode or wash away the Apollo astronauts' mark on the moon. That means their footprints, roverprints, spaceship prints, and discarded materials will stay preserved on the moon for a very long time.
  They won't stay on there forever, though. The moon still a dynamic environment. It's actually being constantly bombarded with "micrometeorites," which means that erosion is still happening on the moon, just very slowly.
  Source: Space.com
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 5. 99% of our solar system's mass is the sun.

• ​
  
  Our star, the Sun, is so dense that it accounts for a whopping 99% of our entire solar system. That's what it allows it to dominate it gravitationally. Technically, our Sun is a "G-type main-sequence star" which means that every second, it fuses approximately 600 million tons of hydrogen to helium. This means that it also converts about 4 million tons of matter to energy as a byproduct.
  Being the type of star that the Sun is, it also means that when it dies, it will become a red giant and envelop the earth and everything on it. But don't worry: That won't happen for another 5 billion years.
  Source: The Ohio State University Department of Astronomy
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 6. More energy from the sun hits Earth every hour than the planet uses in a year.

• ​
  
  You should be sad to know that solar technology produces less than one-tenth of 1% of global energy demand. This is due to several factors, including how much land is required for solar panels to capture enough energy for a population of people to use, how unreliable it is in bad weather and at night, and how expensive the technology is to install.
  Despite all these drawbacks, the use of solar energy has increased at a rate of 20% each year for the past 15 years.
  Source: National Geographic
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 7. If two pieces of the same type of metal touch in space, they will bond and be permanently stuck together.

• ​
  
  This amazing effect is called cold welding. It happens because the atoms of the individual pieces of metal have no way of knowing that they are different pieces of metal, so the lumps join together. This wouldn't happen on earth because there is air and water separating the pieces. The effect has a lot of implication for spacecraft construction and the future of metal-based construction in vacuums.
  Source: European Space Agency
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER
  
• 8. The largest asteroid ever recorded is a mammoth piece of space rock named Ceres.

• ​
  
  The asteroid is almost 600 miles in diameter. It's by far the largest in the asteroid belt and accounts for a whole third of the belt's mass. The surface area is approximately equal to the land area of India or Argentina. It's so big, there's actually some debate over whether to refer to it as a dwarf planet instead of an asteroid, even if it has mostly asteroid-like qualities.
  Ceres piques our interest specifically, as water in the form of ice has been spotted on its surface. An unmanned spacecraft named Dawn is due to be orbiting the space rock by 2015.
  Source: TheGuardian.com
  IMAGE: FLICKR, NASA GODDARD SPACE FLIGHT CENTER