Do you know how the distance between the earth and the planets is measured? Scientists tell you how

In 1619, the French scientist Kepler explicitly proposed the last of the well-known three fundamental laws of planets. This basic law is very crucial and has key practical significance for future generations to understand planetary astronomy in the solar system. Kepler's Third Fundamental Law states that the square meters of the cycle time of the planets closely orbiting the Sun are positively related to the cubic meters of their semi-major axis. Because the orbit of the planet is elliptical, but the relativity is closer to a perfect circle, so for ordinary people, this semi-major axis can be regarded as the distance between the planet and the sun.

The key practical significance of this basic law includes one: because the revolution period of each planet can be obtained by human eye observation, the proportion of the distance between different planets and the sun is also clear. Therefore, you only need to know the distance of each planet to the sun's light, and you can know the distance of other planets to the sun's light.

It seems that the easiest to measure is the distance between the sun and the earth. Regarding the precise measurement of this distance, experts have clearly put forward thousands of methods, which are limited to the number of articles. Everyone only introduces the most accurate and reliable method at that time, that is, the well-known scientist Halley Motorcycle (that is, the conjecture of Halley's Comet). The one that reverts to cyclic time) explicitly proposed Venus transit method.

If you remember how to measure the diameter of the Earth, folks, a key specialized tool will come to your mind - trigonometry. In the case of estimating the distance between the sun and the earth, the same is reasonable.

The Harley-Davidson idea is that we can use sunlight, Earth, and another star to form 2 triangles, and then use a known side and a perspective to measure the length of the other side. The other star is Venus on the inner side of the earth. Of course, there is not only Venus, but also Mercury on the inner side of the earth, but Venus is closer to everyone, farther from the sun, and easier to observe, so Venus becomes the "best candidate".

Because Venus is on the inner side of the earth, it sometimes blocks between the earth and the sun, which is called "Venus transit".

Harley-Davidson thinks: If we observe the transit of Venus at two very long points on the earth, we will find that the parts it projects on the sunlight are different, so the observer's field of vision will take Venus as the endpoint, and each is facing the direction of the house. One side of the sun and the earth create a diagonal angle. This perspective, we can all be accurately measured.

In addition, for biologists who have already accurately measured the diameter of the earth, it is not a problem to accurately measure the distance between the two observation points. In other words, if you know the included angles and bases of an isosceles triangle, you will know all the other information content. This is also a simple professional knowledge of middle school mathematics.

However, there is a problem here: because the orbits of the planets are not all on the ecliptic, just some inclination (as shown in the figure below). Therefore, although Venus will "drive at high speed" in the earth's orbit once or twice in the middle of a year, it is very likely to pass under the sunlight, causing everyone to see the transit situation. Therefore, the Venus transit occurs after an eight-year interval, and the next one will not be until more than a hundred years later.

Therefore, for experts, the opportunity of observation is very rare.

Harley-Davidson himself has become a deceived person at the intersection of the orbits of the two planets. Although he clearly proposed this method, his unfortunate daily life ended with hatred for more than 100 years of "broken schedule".

In 1761, the transit of Venus started as scheduled, but because Venus was not in a very good position, precise measurements were very imprecise. Eight years later, in 1769, in a chaotic era when every major power in the world is occupying each other, experts risk their lives to study abroad to observe. At that time, it happened to be during the "Second Anglo-French Hundred Years War". In order to better understand the distance between the sun and the earth, the Americans established an order not to attack the American captain Tim Cook (then who brought the key observation data information). It was Captain Cook who discovered the Australian outback).

Finally, when experts obtained precious data and information, they calculated the distance between the sun and the earth: 152 to 154 million kilometers. Although this data information is a little different from the contemporary 149.6 million kilometers, it was also very accurate at that time, and it was a scientific research effect like clearing the clouds and seeing the sun.

After the distance of the day is calculated, the distances of other planets and sunlight are very easy to calculate.

Naturally, it is much easier for us all to accurately measure the distance between the Earth and the Sun. In the case of the sun, the earth, and Venus at three points and one line, Venus is very likely to be between the sun and the earth, or it is very likely to be on the other side of the sun. Therefore, everyone sends radar signals to Venus at these two times, and then calculates the time when the reflector of the data signal returns home, multiplied by the speed of light and divided by 2 (round-trip time), which is the 2-stage on the earth. - The distance of Venus, added together and divided by two, is the distance between the sun and the earth.

When people have calculated the distances of planets, they put their sights further, and want to see the distances of stars outside the solar system planets. So, how to calculate the distance of these stars? Stay in the next issue and introduce in detail