to their calculations, astronomers use special units, which are not always clear to ordinary people.It is understandable, because if cosmic distances measured in kilometers, then the number of zeros to be dazzled eyes.Therefore, to measure cosmic distances common to use much larger quantities: the astronomical unit, light year and parsec.
astronomical unit is often used to indicate distances within our own solar system.If the distance to the moon can still be expressed in miles (384,000 km), the closest to Pluto's path is approximately 4 250 million km, and it is quite difficult to be understanding.For such distances it is time to use the astronomical unit (AU), equal to the average distance from the Earth's surface from the sun.In other words, 1 AUIt corresponds to the length of the semi-major axis of the orbit of our Earth (150 million. km.).Now, if you write that the shortest distance to Pluto is 28 AU, and the longest path may be 50 AU, it is much easier to imagine.
next largest - a light-year.Although it includes the word "year", it is not necessary to think that it is about time.One light year is 63,240 AUThis is the way, which does a ray of light for 1 year.Astronomers have calculated that from the very far corners of the universe light beam gets to have more than 10 billion. Years.To imagine this huge distance, we write it in kilometers: 95000000000000000000000. Ninety-five billion trillion kilometers usual.
The fact that light travels not instantaneously, but with a particular speed, the researchers began to suspect since 1676.That's when Danish astronomer Ole Roemer named noticed that eclipses of Jupiter's moon begin to lag, and it happened at a time when the Earth in its orbit heading to the opposite side of the Sun, the reverse of that which was Jupiter.It took some time, the Earth began to come back, and once again began to eclipse approach is still scheduled.
thus been observed for about 17 minutes to the time difference.From this observation, it was concluded: the light at a distance of the length of the diameter of Earth's orbit took 17 minutes.Since it has been proven that the diameter of the orbit is about 186 million miles (Now this constant is 939 120 000 km), it turns out that the light beam moves at a speed of about 186,000 miles in 1 second.
Even in our time thanks to Professor Albert Michelson, who set out to determine as precisely as possible, what is a light year, by another method was obtained the final result: 186,284 miles in 1 second (approximately 300 km / s).Now, if you count the number of seconds in a year and multiply by the number, then we find that the length of a light year is 5 880 000 000 000 miles, which corresponds to 9,460,730,472 580.8 km.
For practical purposes, astronomers often use this as a unit of distance parsecs.It is a shift of stars on the background of other celestial bodies 1 '' at displacement observer at 1 radius of the orbit of the Earth.From the Sun to the nearest star (Proxima Centauri, is in the Alpha Centauri system) 1.3 parsecs.One parsec equals 3.2612 St.years or 3,08567758 × 1013 km.Thus, a little less than a light-year-thirds of the parsec.
