My Science School

For a planet to be habitable for humans, 1) it should be at a safe distance from the Sun - should be neither too hot, nor too cold; 2) it should contain liquid water, and 3) it should have a protective atmosphere that keeps the Sun's radiation out. There is only one planet in the solar system that satisfies all these conditions and that planet is Earth. The next best option is Mars.

Mars has many advantages. It is very close to Earth - humans can reach the Red Planet in less than six months from Earth.

A Martian day is just over 24 hours long, roughly equivalent to a day on Earth. Mars has an atmosphere (though a thin one) that offers protection from cosmic radiation and solar radiation. Gravity on Mars is 38% that of Earth, which is believed by many to be sufficient for the human body to adapt to.

Evidence suggests that water may exist in the subsurface all over Mars. With help from technology, humans can survive on Mars, whereas the survival chances are slim on other planets and their moons.

 

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If last week's story on the birth of the Moon fascinated you here's another quick fact about the Moon that is sure to grab your attention - your weight on the Moon would be much less compared to that on Earth! Yes, that's true. Here's why.

It all comes down to gravity

Your weight is a measure of the amount of gravity exerted on your body. Since gravity on each of the planets and space bodies is different your weight at any two places is bound to be different.

The gravity of an object is determined by its mass and size. Since the Moon is considerably smaller than Earth in mass, the gravity exerted on your body on the Moon is also much less - one-sixth that of Earth to be precise. However, even if you go to the Moon, only your weight will change, while your mass will remain the same as that on Earth. Actually, your mass anywhere in the universe is pretty much the same.

That makes your weight...

When you land on the Moon's surface, your weight would be one-sixth of your current weight here.

For example, if you weigh 60 kg on Earth, your weight on the Moon's surface would be about 10 kg.

 

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People often see animations of earth rotating on TV in the opening of news shows, sporting events and other kinds of motion graphics, but those are just animations. And they are not realistic

The fact is that even though the Earth rotates at over 1,000 miles per hour at the equator (1,037.54 mph to be exact), and slower as you go north or south. If you were out in space far enough away from the earth to see the whole planet it would appear to turn so slowly that it would appear motionless.

The picture below shows how far the Earth turns in 1 hour. For a comparison imagine you're looking at a clock. The hour hand doesn't look like it is turning, but it actually turns twice as fast as the Earth.

 

Credit : Quora

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 The one animal I found the most interesting regarding visually seeing the stars is the Dung Beetle!

Yes, would you believe the dung beetle uses the milky way for navigation?

Apparently the dung beetle is actually pretty smart. Other than playing with poop, that is. Some really unfortunate scientists got to spend some quality time with one of the most maligned creatures on the earth. But what they found was nothing short of amazing. They had known for some time that the beetle used the polarized light from the sun for navigation, but what did they do at night? They thought it could be the moon, but what about moonless nights? It turned out that they were using the milky way, which was confirmed by taking them to a planetarium. They found that the beetles used the visual cues of the milky way instead of something like the magnetic field.

They confirmed this in the field by giving the beetles cool hats like what you see here (the control group got transparent hats). The beetles with the opaque hats could not navigate.

 

Credit : Quora

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Planets orbit stars because they are not traveling fast enough to escape the star's gravity well but are traveling fast enough to not fall into the star.

Stars are massive. That mass causes spacetime to curve. The curvature of spacetime is gravity.

But you must imagine that it is 3-dimensional. So, a gravity well is like a funnel. The planet is in the funnel and must travel around it to not fall further into it. 

The coin can't escape because it would need an added force to accelerate it. In the case of this funnel, friction slows the coin down, so it does eventually fall in to the center.

Remember Newton's First Law of Motion:

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force.

The forces are balanced for a planet, so it just keeps on doing what it was doing.

 

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The .220 Swift remains the fastest commercial cartridge in the world, with a published velocity of 4,665 ft/s (1,422 m/s) and the escape velocity of the MOON is 2,400 m/s so the bullet will not leave the vicinity of the Moon and will eventually return to the surface.

And to respond to the dozen’s of people who have commented below that a rifle bullet will not work in space or on the Moon , yes it will , and actually , like a rocket it will work marginally better . A bullet carries it’s own oxygen in it’s propellant powder and does not need air to ignite !

The only ballistic (Non missile) round that would leave the moon would be one coming from a rail gun which can reach a velocity of upwards 5–6000 m/s (21,600 km hr).

If aimed very accurately which would be very difficult to do it could enter the earth’s atmosphere at a speed in excess of 40,000 km/h or 11,100 m/s .

As the projectile enters the Earth’s atmosphere it will compress the air ahead of it to a temperature of 8000–10,000ºC and melt and burn up , not striking the ground but vaporizing 15 -20 kilometers above ground maybe terminating in a loud explosion.

 

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It’s not the fall that kills you, it’s the sudden stop at the bottom.

Bouncing doesn’t come into it. The question is, how fast are you going when you hit something. The faster you are going, the more energy you contain when you hit the ground—energy that now tries to break bones and crush organs like tomatoes on the windscreen of a passing car.

On Earth, the general rule of thumb is that you risk serious injury from any fall higher than you are. On the moon that would have to be adjusted; lunar gravity is only 1/6th as strong, but there is no air—so you will never reach a “terminal velocity” beyond which you don’t speed up any further.

If an astronaut fell 300 feet on the moon, that’s a 91.44 meter drop at 1.633 meters per second per second acceleration (we’ll do this in metric because metric isn’t a stupid, byzantine measuring system). With no air resistance at all, our hapless astronaut will hit the ground after 10.6 seconds, at a velocity of 17.2 meters per second.

How dangerous is that? Well on Earth, to hit the ground at 17.2 meters per second (ignoring air resistance), you’d have to fall from a height of 15.2 meters, or 49.8 feet, or the roof of a five story building. Onto rock or dry sand. Does that sound like a good idea?

No. Such a drop would likely break the spacesuit and would certainly break the occupant.

 

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The outside of the ISS can reach temperatures as high as 250 degrees F (121°C) on the sunny side and as low as -250 degrees F (-157°C) on the shady side. Inside the ISS are plenty of things that generate heat – such as human bodies, laptop computers, pumps, and other electrical devices. It takes a lot of work and complicated thermal control systems to remove that heat from its sources and transport it outside where it can be radiated to space.

For the parts of the ISS that do need active effort to keep warm, that is accomplished using simple electrical resistance heater pads, like the one shown in the below picture. They work on a simple premise – the thin pad has a wire running back and forth and back and forth many times within it. That wire is attached to an electrical source and electricity flows through the wire. The circuit has resistance and resistance results in heat. The wire gets warm, so the pad gets warm, and so whatever surface it is adhered to will also get warm. A thermostat will measure the temperature in that vicinity and the value of that temperature will be used to turn the electrical circuit for the heater pad on and off. There are hundreds of these pads throughout the vehicle.

It is important to use these heater pads to keep the shell of the vehicle warm, because if the temperature drops below the dew point, condensation will form on that surface. Accumulations of water can cause problems with electrical equipment and can promote the growth of microorganisms.

 

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It isn't true that travel can only occur every two years, but the conditions are far more optimal at those times, essentially making other times unconsidered.

There are different types of Earth-Mars mission trajectories. They don't all start when Mars and Earth are close. There are multiple factors involved, including whether or not the spacecraft is to come home, whether a gravity assist from Venus is available, and the capabilities of the launch vehicle. However, for the typical one-way mission to get a probe or rover to Mars, we do indeed launch when Mars and Earth are fairly close.

Mars and Earth are at their closest to each other when they are at opposition. However, we don't actually want to launch at this point. We want to launch before this point.

We want to use a minimum energy transfer orbit in order to use the least amount of fuel. A Hohmann transfer orbit does this. Our spacecraft starts at Earth's orbit. A Hohmann transfer orbit uses a burn at the starting point (periapsis) that increases the aphelion of the orbit such that it occurs at the orbit of Mars. This will be 180-degrees later in the orbit.

So, our goal is to time the launch such that Mars will be at that same location when the spacecraft gets there. Since Mars is in a larger orbit, it takes longer to move the same angular distance as the Earth. That means we need Mars to be ahead of Earth when we launch our spacecraft.

We calculate the period of the orbit that our spacecraft will be in. That turns out to be about 520 days. Our spacecraft is traveling half of an orbit, so our trip will be about 260 days. Mars has an orbital period of 687 days. In 260 days, Mars will travel an angular distance of 136 degrees. That means the optimal time to launch the spacecraft is when Mars is 44 degrees (180-136) ahead of Earth in its orbit, as shown below. That means we launch the spacecraft about three months before Mars and Earth are at their closest.

 

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On Earth, gravity pulls down on us. In the standing position, that means our head is pressing on our neck, our neck is pressing on our torso, our torso is pressing on our legs, and our legs are pressing on our feet. We lie down, partly, because in doing so we spread the load across our body, taking a lot of stress off of the lower parts of our body.

We also lie down because it leaves us in a stable position, so we don't have to worry about losing our balance and falling, once we are asleep and no longer actively maintaining our balance.

In an orbiting spacecraft, we are in free fall, so we experience weightlessness. All of those red arrows (loads from gravity) disappear. The body now experiences no change in loading from the vertical to the horizontal position. Both are equally stable and both feel the same.

So, sleeping is done in whatever position best fits the available room.

 

Credit : Quora

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