Is, or will, our Sun also become a variable star? If so, what kind?

Not a variable star with fluctuating brightness, but our sun is getting brighter gradually over time. As the fuel in the sun is spent the sun gets 10% brighter and 10% hotter every billion years. So we estimate in a couple billion or so years the oceans will dry up and all life on Earth will cease. Earth will become much like Venus is now. Eventually the sun will turn into a red giant and expand to swallow Mercury, Venus and probably Earth.

On what planet should we build the first non-Earth city?

I know. It’s sad. Depressing really. Humans will never build a city off our planet Earth.

I say this because of distances. Even if we were to find a planetary candidate, it would take hundreds or thousands or more years to go one way to visit it just to see if the candidate is really like we need, what to speak of building a city.

Distances in space are unimaginably big. Let’s say the nearest star is 4 light years away. There is no guarantee there is life over there, but to travel that 4 light years will not take 4 years, or 40 years. At the fastest speed ever achieved it would take at least 150 years each way.

Suppose we wanted to take a closer look at the Trappist-1 system, 40 light years away. It is the next best candidate for life. That would take a mere 1,500 to 2,000 years to go one way just to see if anything really was habitable, what to speak of building a city.

Sadly, this is indeed science fiction. We want it to happen, so badly, but it never will happen. At most we might leave some foot prints on Mars and send some robotic systems to the moons of Jupiter and Saturn, but that’s it. Long before our sun blows up, life on Earth will be extinguished.

How many earth years would it take to travel to the sun?

The New Horizons space craft set a record at 36,000 miles per hour, the fastest spaceship relative to Earth ever achieved. The sun is 94 million miles away, so if you divide 94 million by 36,000 mph you come up with 2666.67 hours, or 111.111 days. That’s about 3 months and 21 days, round out to 4 months to be safe.

However, you can’t just launch a space ship from Earth directly at the sun and expect to go 36,000 mph. New Horizon’s speed was achieved through slinging around planets, what we call “gravity assist.” Your sun bound space craft would begin slowly and take a very long time to reach the sun.

If it took the Apollo astronauts 3 days to go 250,000 miles to the moon. At that speed it would take just over 3 years to reach the sun.

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If a tennis ball flies at 99% of light speed, will it be in every location of its trajectory, or will it skip some on its way?

The tennis ball will not appear in every location of it’s trajectory nor will it skip some on it’s way. It will look to us that time on the tennis ball has slowed down.

Time and space are relative. What this means to your question is simply the speed of the tennis ball must be measured in relationship to something else, namely us on Earth.

If the tennis ball is launched from Earth and goes 99% the speed of light from Earth, then microbes and insects on the tennis ball would appear to be moving very slowly. But on the tennis ball, life would go on normally and life on Earth would appear to be going very quickly.

However, on the tennis ball itself, once that speed is achieved, it will appear that the tennis ball is standing still and Earth is moving away very quickly. If you were little and stood on the tennis ball and turned on a beam of light, the light would leave your flashlight at the speed of light in all directions.

Screenshot_2017-04-04_20-31-08How is that possible since light only travels the same speed in a vacuum? Because time slowed down for you, and so light always travels the speed of light, even though you seem to be normal. That’s why space and time are interwoven in the same fabric, what we call spacetime.

The same for us on Earth. We are orbiting the sun, the sun is orbiting the Milky Way center, the whole galaxy is about to collide with Andromeda, etc. etc. But as far as we’re concerned, we’re standing still and light leaves our beams of light at the speed of light.

What percentage of the earth’s water is tied up in the atmosphere (clouds)?

Great question and I don’t know. But this graphic will help us understand together:

Here you can see that there’s not much water on Earth. Basically the earth has high and low areas. The low areas have water. To us the oceans seem deep – 7 miles, maybe more, but overall, compared to the size of the planet, it’s really not much water. We can also see from the image above that we really don’t have a lot of air.

That being said, common sense tells us that not all the water is in the atmosphere. Only some, otherwise we’d have no lakes, rivers or ocean! So I’m going to guess – that’s scientifically called an educated guess, not a large percentage of Earth’s water is tied up in the atmosphere.

Now we could research this more with some Google searches, but my answer is just about common sense. I don’t think that much of our total water is in our atmosphere. There’s some, but we still need some left over to fill the lakes, rivers and oceans too.

 

Why do aliens always have to look and have similar biology to us?

Exactly! To date, no life has been found on any other planet or meteor. We would really like to find life elsewhere, and the most likely candidates within reach would be the moons of Jupiter and Saturn.

Beyond that you have to go interstellar. Since it would take hundreds or even thousands of years to reach even the nearest stars at the fastest speed we’ve ever achieved in space, interstellar travel is unlikely now or in the future.

Put away Star Trek and Star Wars. Aliens are not visiting us and we are not going to visit them, whatever they may look like.

What would happen to the rest of the planets if Uranus changed places with Mars and Pluto swapped with Jupiter?

On this planet there would be total chaos in the classroom. Books would have to be rewritten.

Scientists would be busy figuring out how this happened when it should not be able to happen. It would be on the nightly news with Lester Holt.

Donald Trump would blame it on Democrats.

Immediately on Earth we would see no change except in conspiracy theories.