Distances in space. Astronomical unit, light year and parsec

For their calculations, astronomers use special units of measurement, which are not always clear to ordinary people. It is understandable, because if the space distances were measured in kilometers, then the number of zeros would ripple in the eyes. Therefore, to measure space distances it is customary to use much larger quantities: astronomical unit, light year and parsec.

An astronomical unit is often used to indicate distances within our native Solar System. If the distance to the Moon can still be expressed in kilometers (384,000 km), then to Pluto the closest path is about 4,250 million km, and this is already difficult to understand. For such distances, it is time to use an astronomical unit (au), equal to the average distance from the Earth's surface to the Sun. In other words, 1 au Corresponds to the length of the major semiaxis of the orbit of our Earth (150 million km.). Now, if we write that the shortest distance to Pluto is 28 AU, and the longest path can be 50 AU, it is much easier to imagine.

The next largest is the light year. Although there is the word "year", do not think that it's about time. One light-year is 63 240 AU. This is the path that a ray of light makes for 1 year. Astronomers calculated that from the very distant corners of the universe a ray of light reaches us for more than 10 billion years. To imagine this huge distance, we will write it in kilometers: 95000000000000000000000. Ninety-five billion trillions of habitual kilometers.

The fact that the light does not spread instantly, but with a certain speed, scientists began to guess since 1676. It was at this time that a Danish astronomer named Ole Remer drew attention to the fact that the eclipses of one satellite of Jupiter began to lag, and this happened precisely when the Earth was traveling in its orbit to the opposite side of the Sun, the inverse of where Jupiter was. After some time, the Earth began to return back, and the eclipses again began to approach the previous schedule.

Thus, about 17 minutes of the time difference was noted. From this observation, a conclusion was drawn: it took 17 minutes for the light to travel the distance to the diameter of the Earth's orbit. Since it was proven that the orbit diameter is about 186 million miles (now this constant is 939,120,000 km), it turned out that the light beam is moving at a speed of about 186,000 miles per second.

Already in our time, thanks to Professor Albert Michelson, who set out to determine as accurately as possible what the light-year is like, by a different method the final result was obtained: 186,284 miles per second (about 300 km / s). Now, if we calculate the number of seconds in a year and multiply by this number, we get that the light year has a length of 5,880,000,000,000 miles, which corresponds to 9,460,730,472,580.8 km.

For practical purposes, astronomers often use such a unit of distance as parsec. It is equal to the displacement of the star against the background of other celestial bodies by 1 "when the observer shifts by 1 the radius of the Earth's orbit. From the Sun to the nearest star (this is Proxima Centauri in the Alpha Centauri system) 1.3 parsecs. One parsec is 3,2612 sv. Years or 3,08567758 × 1013 km. Thus, the light year is slightly less than the third part of the parsec.