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----------------------- 2235 - Astronomical Distances
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- Measuring distances in astronomy is looking backwards in time. When there is a flash of lightning, then seconds pass until we hear the rumble of distant thunder. We hear the past. We are seeing into the past too. The lightning flash is faster but it still takes some time for it to reach you.
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- While sound travels about a kilometer every three seconds, light travels 300,000 kilometers every second. When we see a flash of lighting three kilometers away, we are seeing something that happened a hundredth of a millisecond ago. While you can count to 9 before you hear the thunder.
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- We can see seconds, minutes, hours and years into the past with our own eyes. Looking through a telescope, we can look millions and billions of years into the past.
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- When we look at the Moon, we are seeing it as it was just over a second ago.
- The Moon is our nearest celestial neighbor - a world with valleys, mountains and craters. It’s also about 380,000km away, so it takes 1.3 seconds for light to travel from the Moon to us. We see the Moon not as it is, but as it was 1.3 seconds ago.
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- The Moon doesn’t change much from instant to instant, but this 1.3-second delay is perceptible when mission control talks to astronauts on the Moon. Radio waves travel at the speed of light, so a message from mission control takes 1.3 seconds to get to the Moon, and even the quickest of replies takes another 1.3 seconds to come back.
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- It’s not hard to look beyond the Moon and further back in time. The Sun is about 150 million km away, so we see it as it was about 8 minutes ago. If the Sun blinked to black you would not know it for 8 minutes later
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- Even our nearest planetary neighbors, Venus and Mars, are tens of millions of kilometers away, so we see them as they were minutes ago. When Mars is very close to Earth, we are seeing it as it was about three minutes ago, but at other times when Mars is orbiting on the opposite of the Sun light takes more than 20 minutes to travel from Mars to Earth.
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- This presents some problems if you’re on Earth controlling a Rover on Mars. If you’re driving the Rover at 1km per hour then the lag, due to the finite speed of light, means the rover could be 200 meters ahead of where you see it, and it could travel another 200 meters after you command it to hit the brakes.
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- Not surprisingly, Martian Rovers aren’t breaking any speed records, traveling at 5 centimeters per second , or 0.11mph, with rovers following carefully programmed sequences and using on-board computers to avoid hazards and prevent punctures.
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- The finite speed of light presents some challenges for driving on Mars.
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- Let’s go a bit further out in space. At its closest to Earth, Saturn is still more than a billion kilometers away, so we see it as it was more than an hour ago.
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- When the world tuned into the Cassini spacecraft’s plunge into Saturn’s atmosphere in 2017, we were hearing echoes from a spacecraft that had already been destroyed more than an hour before.
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- The night sky is full of stars, and those stars are incredibly distant. The distances are measured in light years, which corresponds to the distance traveled by light in one year. That’s about 9 trillion kilometers. That is 6 trillion miles at 93 million miles per hour.
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- Alpha Centauri, the nearest star visible to the unaided eye is at a distance 270,000 times the distance between Earth and the Sun. That’s 4 light years. We see Alpha Centauri as it was 4 years ago.
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- Some bright stars are much more distant still. Betelgeuse, in the constellation Orion, is about 640 light years away. If Betelgeuse exploded tomorrow, and it is about to explode one day, we would not know about it for centuries.
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- Even without a telescope we can see much further. The Andromeda galaxy and the Magellanic Clouds are relatively nearby galaxies that are bright enough to be seen with the unaided eye.
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- The Large Magellanic cloud is 160,000 light years away, while Andromeda is 2,500,000 light years away. For comparison, modern humans have only walked the Earth for about 300,000 years.
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- With the unaided eye you can look millions of years into the past, but how about billions pf hears using an amateur telescope.
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- Quasar 3C 273 is an incredibly luminous object, which is brighter than individual galaxies, and powered by a huge black hole. But it is 1,000 times fainter than what the unaided eye can see because it’s 2.5 billion light years away.
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- A bigger telescope allows you to peer even further into space. A Quasar APM 08279+5255 is just a faint dot in a telescope but it is 12 billion light years away.
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- Earth is just 4.5 billion years old, and even the universe itself is 13.8 billion years old. Astronomers have looked back across almost the entire history of our universe.
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- So when you look up, remember you aren’t seeing things as they are now; you’re seeing things as they were. Without really trying, you can see years into the past. And with the aid of a telescope you can see millions or even billions of years into the past with your very own eyes.
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- Astronomers are historians. Everything they see happened a long time ago. Like archeology they are constantly looking at the past. Of course , none of us can look into the future or we would already be rich. The past is the best thing we got going for us. Make good use of it. Here are other Reviews:
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- 2172 - If this peaks your interest be sure and read this Review. Extremes in astronomy. If a human were to become a blackhole he would be compressed to the size of a proton.
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- 2125 - Astronomy’s strange discoveries. The deadliest blast of gamma rays happened on March 19, 2005 in the Constellation Bootes and you could see with your naked eye. Even though it was 7,500,000,000 lightyears away.
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- 1910 - Space explorations in 2016. Many small steps into our solar system with unmanned robots.
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- 1909 - My lifetime in astronomy in review. Years: 1941 to 2017
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- 1906 - A century of astronomy. Years; 1906 to 2011. Also listing 8 more Reviews available.
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- 1867 - Questions in physics and astronomy.
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- 1742 - Astronomy facts one.
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- 1716 - Astronomical disappointments. Sometimes missions go wrong.
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- 1615 - 1616 - 1617 - Key discoveries in astronomy.
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- 1614 - Problems to be solved in astronomy.
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- 1493 - Puzzles in astronomy.
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- 1108 - How far does the astronomical ladder reach
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- 942 - Last 35 years in astronomy.
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- 758 - Ancient astronomers.
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- 714 - A new astronomy.
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- (Listed above are more reviews on this subject, available if requested)
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- January 12, 2019
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- to: ------- jamesdetrick@comcast.net ------ “Jim Detrick” -----------
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-------------------------- Saturday, January 12, 2019 --------------------------
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