What is actually meant by Hindu texts when they said Earth was on top of elephants which were on top of a giant turtle?

 

Is planet Earth on top of four elephants which in turn are on the top of a giant turtle?

What does this mean?

Scriptures are based on seven stage muscle tone based thinking. The fourth stage is symbolized by water and represents Vishnu.

Vishnu is the Preserver and keeps life between a lower limit called Positive attitude and an upper limit called Negative attitude.

The Positive attitude is symbolized by turtle and the Negative attitude by Earth.

In Kurma or Turtle incarnation Vishnu prevents the ocean floor from sinking. The ocean floor symbolizes the Positive attitude.

In Varaha incarnation Vishnu restores the Earth from the bottom of the ocean floor, hidden there by the demon Hiranyaksha. Earth here symbolizes our Negative attitude.

If our Negative attitude below our Positive attitude we will feel that we have achieved more than enough and therefore, we won’t feel like doing anything. Vishnu restores the Negative attitude to its default level.

Purusha / Vishnu are three dimensional at the level of the navel. The four elephants symbolize this fact.

Thus, the Earth on top of four elephants, which in turn are on a giant turble symbolize the default state of human mind.

If Earth was shrunk down to the size of a grape, how big would the Galaxy be?

 Let's round the diameter of a grape up to about one inch (2.5 cm), just for simplicity's sake.

The diameter of the Earth is about 7917.5 miles (12,742 kilometers), which translates to 501,652,800 one-inch grapes. Give or take. That is to say that the Earth is currently 501,652,800 times bigger than a grape, so in order to make them the same size, we would need to scale down the Earth by 501,652,800 times.

We now assume that the same proportional shrinkage takes place in all of space, or at least our galaxy.

Doing this makes the solar system at least navigable. The Sun, which is now about the size of a Smart Car, is a little less than 1,000 feet (about 300 meters) away from our little grape. That’s a short little jog, or about the height of the Eiffel Tower. Be sure to stop to smell Venus on the way — it smells like rotten eggs!

Pluto is still over seven miles (over eleven km) away from the Sun, so we’ll need a vehicle if we aren’t in the mood to hike. Just to arrive at an icy pebble about 1/5 of an inch (1/2 of a centimeter) in diameter. You may (or may not) have noticed Jupiter looking like an overinflated basketball along the way. More likely you noticed Saturn and its spectacular rings, now just under two feet across.

But we’re not thinking big enough. Granted, the Milky Way is a relatively small galaxy, with a distance of "only" about 100,000 light-years across. Scaling that down by the same ratio, the galaxy would now be 0.0002 (1/5,000) light-years across.

To turn that into miles, we must consider that one light-year in reality is almost 5.9 trillion miles (9.5 trillion km). In our scale model, that same light-year is now a little more than 11,718 miles (18,859 km) -- a little greater than the distance from the United Kingdom to New Zealand.

So already we’ve outgrown our car. We’ll need a commercial plane and most of a day to travel a single light year. But if we want to get anywhere, the nearest star will require that we make that trip four times and then some, so we’ll need a high-speed jet with enough fuel to travel completely around the Earth (the real Earth) twice without refueling. (One commenter suggested a rocket, which is probably a better time-saver).

We’ve now made it to the Alpha Centauri system. Congratulations. That flight was probably miserable.

But we’re not even getting started. We’re trying to traverse the galaxy, after all, and we’ve only jumped from one star system to its nearest neighbor.

This scaled-down galaxy is now 1,171,826,372 miles (1,885,871,741 km) across. Essentially we’ve shrunk the Milky Way to fit inside our Solar System; the edges of the galaxy would be found somewhere between the orbits of Saturn and Uranus — still twenty-five thousand times further than humans have traveled thus far. If you want to get a feel for how long that trip would take, I recommend this map (which shows that even light itself would take more than an hour and a half to cover the distance):

If the Moon Were Only 1 Pixel

Even at over 500 million times smaller than actual size, our galaxy is still unfathomably massive.

Moral of the story: I hope you like your little grape. It’s almost definitely the only grape you’ll ever get. Do take care of it.

Note: the above calculations are completely linear. I only used diameter. If accounting for volume, the numbers would be different. For example, I had said that Earth is about 502 million times larger than a grape, but if measured by volume, Earth becomes more than one septillion times larger than the grape… (that’s a 1 with 24 zeroes). To make that useful we’d have to compare it to the volume of the galaxy, but I don’t know how to measure that (and I don’t think anyone else does either). Because I wanted to talk about travel times anyway I felt a linear measure was sufficient.

Why doesn't the ISS crash into the Earth?

 There is a very small air resistance at the altitude of the ISS. This drag causes the ISS to lose up to 5 cm/s (0.1 mph) of velocity and 100 meters (330 ft) of altitude each day.

To compensate for this, about once a month the ISS fires its thrusters to increase its altitude. This maneuver is called a reboost, it is done by modules at the rear of the International Space Station (ISS), such as the Progress, ATV (pictured below), or if necessary the Service Module, itself.

There are two types of reboost - single burn and two-burn. A single burn reboost involves one firing of the thrusters. The impact of the firing is an increase in altitude on the opposite side of the planet. This type of reboost is done for small reboosts because it does change the eccentricity of the orbit.

The general idea is that if we create a delta-v at a point, that delta-v will affect the vehicle throughout its orbit. So in the above picture we can see that for the first half of the orbit (moving counterclockwise) it lifts the ISS away from its nominal orbit. But once we pass the 180 degree point, we can see that the delta-v now lowers the ISS back to its original point.

A two burn reboost essentially starts like a single burn reboost, but at the 180 degree point it fires the thrusters again to cancel out the original delta-v. This results in the ISS being in a new circular orbit at the altitude of the second burn.

The design envelope of the ISS is to keep it between 280 km and 460 km. But we don't usually reboost up to 460 km and then drift down to 280 km. The reason for that is that we don't want to make the visiting vehicles work so hard and burn so much fuel to get up to 460 km.

So, that means we do smaller, more frequent reboosts. They occur about once a month and involve a delta-v of about 2m/s and involves firing thrusters for about 900 seconds, although that is variable depending on which module does the burn.

Most often, reboosts are done by an attached Progress module. We usually use the smaller thrusters on the vehicle, because we do not want the acceleration on the vehicle to greatly affect ongoing payload science. Typically we use four thrusters that each have a force of 13.3 kg-f (29.3 lbf).

Is the Earth floating, flying, or falling?

 When I was in school, I saw the solar system in a 2-dimensional plane like this:

When we look at the solar system in static 3D, we will definitely think about the existence of a hypothetical invisible field that holds the planets and the sun from falling, called ether, like the animation below:

The view of the existence of ether is actually just an illusion and will change when we include the fourth dimension, namely motion, in the solar system simulation, so it will look like this.

Of course, the solar system's helical motion isn't entirely accurate, as the planets' actual tilt around the sun is 60 degrees. So, the most realistic depiction of the solar system's motion is something like this.

It's very complicated, isn't it?

So, is the Earth floating, flying, or falling? I prefer to use the words "thrown" and "bound" by the sun's gravity, which also moves with the galaxies thrown around in this vast universe.

Perhaps someday this explosion will turn into a Big Crunch, and everything will return to its original state, only to explode again, forming a new universe. And so on, endlessly.

What is the hardest substance on Earth?

 Human technology progresses more and more every day. Modern industrial processes require materials capable of withstanding immense pressures while retaining their shape and integrity. For this, engineers generally turn to metals due to their wide availability and malleability.

But what is the strongest metal, and just how strong is it?

The answer to this question depends on how the question itself is framed. Does the practicality of using a metal in any significant amount count? Does it have to be a natural metal, or are alloys considered? What's the difference between strength and hardness? This article attempts to examine the multiple answers to this question, covering each metal with a claim to the title, and arguing its case.

Note: For the sake of clarity, the 'strength' considered is tensile strength, which is how much force an object can withstand before warping, unless otherwise stated.

The Strongest Natural Metal: Tungsten

As far as pure metals go, tungsten has the highest tensile strength, with an ultimate strength of 1510 megapascals. Tungsten also has the honor of having the highest melting point of any unalloyed metal and the second highest melting point in the whole periodic table—only carbon can withstand hotter temperatures. Tungsten is very dense and brittle, making it difficult to work with in all but its purest forms. Tungsten is commonly used in electrical and military applications, and you may find tungsten filaments in light bulbs and tungsten coating that adds a real punch to projectiles. It is also a common component in steel and other alloys, where even a small amount can significantly increase the strength of the alloy.

A megapascal (MPa) is a metric pressure unit, mostly used in hydraulic systems that gauge high pressure ratings, that equals 1,000,000 newtons per square meter (which is a pascal). 1 MPa is equal to 10 Bar.

The Strongest Alloy: Steel

Alloys are a constantly changing field, as researchers attempt to create ever-stronger combinations of elements. Generally, the strongest alloy is steel mixed with a few other elements. Vanadium steel alloys seem to be particularly promising, with several companies releasing variants with ultimate strengths of up to 5205 MPa. The steel that holds this distinction is called Micro-Melt® 10 Tough Treated Tool Steel.

Steel itself is an alloy of iron and carbon, although other elements can also be used. Steel is a highly versatile alloy, meaning a form of it can be made to meet almost any specifications. Steel has been in use for millenniums but became a more exact science during the Renaissance (1300-1700).

The Hardest Metal: Chromium

The 'hardness' of a mineral is generally determined by the Mohs scale and is defined as the scratch resistance of a mineral. Diamonds are the hardest minerals known to man, but what is the hardest metal? That honor goes to chromium, a metal perhaps best known as the key ingredient in stainless steel. Chromium is also commonly used in chrome plating, which acts as a form of protection against corrosion and physical damage.

Chromium has been recognized for its unique traits since the Qin Dynasty in China, when weapons and armor were coated with the metal and survive to this day, uncorroded and in perfect shape.

The Most Useful Strong Metal: Titanium

With an ultimate strength of about 434 MPa, titanium is the perfect blend of strength and practicality. Its low density makes it perfect for industrial uses requiring a strong metal with a high melting point. Indeed, titanium has the highest strength-to-weight ratio of any natural metal known to man. Pure titanium is stronger than standard steel, while being less than half the weight, and can be made into even stronger alloys. Because it is also fairly common, it's no wonder that titanium is used for a multitude of purposes. When it comes to manufacturing, the only strong natural metal worth caring about is titanium.

These metals are the backbone of modern industry, providing the support that keeps our daily lives running smoothly. Whether in the tip of a pen, on the fuselage of an airplane, or in the beams of a tall building, we rely on metals to protect us as we seek to progress ever further. We should consider ourselves lucky that, no matter what our needs, there is something in nature to cover them.

Will the Earth ever end?

 Yes, everything that has a beginning has an end.

The Earth, our home planet, is no exception.

The most likely scenario for its demise will be during the end of the main sequence for the Sun, in 7.88 billion years, where it has expended its hydrogen fuel and can no longer maintain hydrostatic equilibrium. It grows in volume exponentially to become a Red Giant. This will likely consume the Earth (and the Moon) utterly, they will become part of the Sun and no trace or evidence of its existence will remain.

If the eventual radius of the Sun does not exceed 150,000,000 km (1 AU), then the Earth will just get a front row seat of the helium flash, with the Sun filling the sky and surface temperatures exceeding those that boil carbon, it becomes vapour and part of the Sun’s photosphere.

It’s worth noting that no living things will perish at this time, as the Sun is increasing in luminosity and temperature by around 1% every 100 million years. So a billion years from now, and 6.8 billion before the Red Giant phase, the surface temperature on Earth will not support liquid water, the oceans will boil away, and all life as we know it will cease to exist.

Mars will survive the clutches of the expanded Sun, but have a surface temperature similar to Mercury now. Interestingly, the moons of Jupiter and/or Saturn might be hospitable (in purely a temperature sense) and allow liquid water on their surfaces.

If this fate, of the Earth becoming inhospitable to life in around a billion years, distresses you (in a philanthropic sense, as you’ll be long gone) then it shouldn’t.

This is what a human ancestor looked like 1 billion years ago:

No, not the dude next to the pick-up (he came along a little later), the green slime - Cyanobacteria - on the water.

These steps are not to scale, we have only been humanoids for around 4 million years, and only strictly human for 160,000 years:

So you can imagine, regarding how evolutionary development has sped up over time, what our descendants might look like in another 1 billion years. Or rather, you can’t imagine, but you get the idea.

Even without the exponential acceleration of our evolution allowed for by technology, and the unimaginable forms of meta-humans in just one thousand years, our descendants will not be anything vaguely resembling humanity by the time the Earth gets too hot to harbour life.

So the Earth will end, but it’s highly unlikely that what we become in the future will end with it. If we don’t manage to at least populate our solar system or build space habitats by then, it will be the worst case of under-achieving the Universe has seen since the Kjorg of Andromeda were gifted omniscience by an ancient pure energy culture and the chance to sublime, and decided to drink cocktails on their favourite beach planet instead.

Why don't we get eclipses from other planets between the Earth and our Sun?

 We do, actually!

We even have eclipses from other planets between the Earth and the OTHER STARS!

Only they are known by a different name, so you probably don’t know them as eclipses.

Before I get to them, check out this eclipse of Mercury.

Source Image: Transit of Mercury - Wikipedia

See the black dot I’ve marked in the green circle? That’s Mercury between us and the Sun.

The smudge inside the blue circle is the sunspot. Notice how it’s bigger than the planet of Mercury.

In this image, Mercury is fully intent on blocking the Sun’s light from ever reaching us. But the poor guy is too small to have any meaningful impact.

So, we don’t even notice it.

In fact, Mercury’s obstruction of our view of the Sun is so unremarkable that it’s not even called an eclipse. The same goes for Venus, too.

No effect, but A+ for effort!

When is an Eclipse Not an Eclipse?

During a solar eclipse, the Moon blocks the Sun either fully or partially. Either way, the Moon is capable of blocking a substantial portion of the Sun when viewed from the Earth.

Remember, it’s not the actual size of the Moon that matters here, but its apparent size in the sky.

Since its apparent size in the sky, as seen from Earth, is large enough to block the Sun partially or entirely, its obstruction is known as an eclipse.

Now, would you call it an eclipse if an asteroid just happened to whizz past the Earth between us and the Sun?

You wouldn’t, because it’s simply too small to qualify as an eclipse!

That’s what happens when Mercury or Venus ends up between the Earth and the Sun. They’re just too small for us to experience an eclipse.

So, we call those events Transits!

Transits are Among the Most Important Events in Astronomy

Did you know that planets outside the solar system are too dim to be visible to us?

Several factors, including interstellar dust, brightness of the accompanying star, etc., make it almost impossible for us actually to see these exoplanets even with our most sophisticated telescopes.

So, how do we detect them?

We rely on transits.

When a planet passes before its home star, there’s a small drop in that star’s brightness.

Our sophisticated instruments are capable of detecting and measuring that drop in brightness. Based on this, we ascertain the existence of a planet around a faraway star.

In short, these “eclipses” or “transits,” whatever you wish to call them, play a central role in helping us detect planets outside the solar system.

The Moon is slowly drifting away from Earth

 Believe it or not, the Moon is slowly drifting away from Earth—about 3.8 cm (1.5 inches) every year! It might seem tiny, but over millions of years, this gradual shift is rewriting Earth’s cosmic story.

🔄 What’s Going On?

🌊 The Moon’s gravity pulls on Earth’s oceans, creating tides.

🌀 Those tides push back, nudging the Moon farther out.

⏳ As a result, Earth’s spin slows down—our days are getting longer!

🚀 What’s Ahead?

🌑 One day, total solar eclipses will be a thing of the past—the Moon will be too far to fully block the Sun.

🌊 Tides will weaken, transforming ocean patterns.

🔒 Eventually, Earth and the Moon may lock into a mutual orbit, always showing the same face to one another.

The Moon isn’t just orbiting us—it’s slowly waving goodbye. 🌌🌙✨

What are some of the best rare natural phenomena that occur on Earth?

 Stunning Turquoise Ice in Lake Baikal

Asperatus Clouds

Manhattanhenge — sometimes referred to as the Manhattan Solstice — is a circumstance which occurs twice a year, during which the setting sun aligns with the east–west streets of the main street grid in the borough of Manhattan

Milky Way arching over a Joshue Tree in California

Enchanted River

Enchanted River is found in Barangay Talisay, Hinatuan, Surigao del Sur. It is called "enchanted" because no one has ever reached its bottom.

The largest and deepest natural funnel on Earth

 The largest and deepest natural funnel on Earth is called Xiaotsai Tiankan.

It is located in the center of China, Penzhi. This amazing funnel is completely natural and measures 662 meters deep and 537 meters wide. But the most impressive thing is the diversity of life it contains.

Geologists are surprised by the influence of water on Xiaotsai Tiankan. A funnel was formed at the top of the cave, where an 8.5 kilometer long underground river falls into a beautiful waterfall. Thanks to its huge size it is the deepest karst funnel in the world.

It is home to about 1,300 species of plants and wild animals. Among the most interesting inhabitants of the underground forest is the misty panther, known to the locals since ancient times.