Every branch of science has its own measurement units. The units of distance measurement are used as per the requirement in every branch of science. For example, a material scientist will measure at most microns (10^{– 6}m), at the same time on atomic physicist atstrogram (10^{– 10} m), an atom physicist firmi (10^{– 15} m) will measure. We know that the standard SI unit meter (m) for measurement in distance, but this unit is not easy to use in every branch of science. Measuring the diameter of an atom in meters or kilometers would be cumbersome. Therefore selection of units is necessary according to study and use. So, what unit is used for measuring distance in astronomy? In this article we will learn about the astronomical unit – au, light year (light year-ly) and parsec.

Distance Measurement and Units

Unlike the quantum systems that the Universe is extremely vast. So huge that kilometer is very small unit. So astronomers created a new unit system for distance measurements. In this article we will discuss the three main units of this system which you will find in most astronomy articles and books. These are the three units, the light year, the parsek and the astronomical unit (au)). These are used according to the distance value. The astronomical unit is used for the distance between planets in the solar system. Light year and parsek are used to discuss the distance of nearby stars, whereas kilparsakes and megaparsake are used for the distance between galaxies.

Astronomical Unit (AU)

The astronomical unit is called the average distance between the Sun and the Earth. It costs 149, 597,870,700 meters or 15 million kilometers (9.3 million miles).

We know that the orbit of the Sun (or the Sun) of Earth (or any other planet) is not circular. It is an elliptical. Therefore, the distance from the sun’s Sun changes throughout the year. At the beginning, the definition of a celestial unit was deemed equivalent to the subhead axis of the Earth’s orbit. But in 1976, the International Astronomical Union (IAU) changed it to more accuracy and precision. Now the definition of the celestial unit is the radius of such a circular orbit of a massless particle, in which the time taken for the orbiting time is 365.2568983 days or a Gaussian year.

An Astronomical Unit (AU) for the accuracy of which is the distance at which the value of the heliocentric gravitational constant (G * M☉) is (0.017 202 093) ², AU³ / d². M☉ = The mass of the sun.

The importance of astronomical unit (AU)

It should be kept in mind that the value of the gravitational constant (G) and the mass of the Sun (M☉) is not known very accurately. But the product of both of these is known more accurately. Therefore, all calculations of planetary motion are mainly done using the astronomical unit and solar mass (M☉). In this way all the results depend on the gravitational constant. These constants are not converted into standard SI units because this change can lead to impurities.

Light year (ly)

The product of the Julian year (365.25 days) and the speed of light (299,792,458 m / s) is called light year. It is the product of time and speed, so this is the distance that the light decides in a Julian year. The price of light year is 9.46 trillion km or 63,241.077. Light year, it is the maternal unit of some other unit lighting units like light seconds, light minutes or light hours. When we say that a body is at a distance of “light-x”, it means that the distance to which light x unit will take time to decide.

Importance of light year

In light of astronomical year, there is a high degree of probation. The biggest advantage of this is also that when we say that this body is so light years away, then we also know how old we are seeing the image of that body. If a body is 4 light years away, it means that the light emitted from that body has taken 4 years to reach us. That is, we are seeing his 4 year old image. In the same way, the Sun is 500 light sheds away, if for some reason the sun disappears then we will know about 500 seconds later.

Parsec (pc)

The value of a parsek is 3.26 light years. Now you must be thinking that there is such a small difference in light year and Parsek, then what is the need for an additional unit? Let’s see

In astronomy, distance from any star is one of the most important methods of measuring the parallax method. In this method, the angle between the two measurements of a position in the sky is measured in the sky. The first measurement in this is on the side of the Earth’s Sun. The second six months after the Earth is on the other side of the sun. In the middle of these two measurements, the distance between the two worlds of the Earth is twice the distance between Earth and the Sun. Now the angle between the two measurements is twice that of the Perllex angle, which is formed between the lines from the Sun and the Earth to that star.

The value of Perlix is that the star has half the angular distance of the wind speed in the sky. In this picture, the star’s position is shown from D, the Sun’s S and the Earth’s position E, and these three objects are making right angled triangles. In this, the position of the star is in the angle opposite the subprime axis of the Earth’s orbit.

Astronomical distance measurement

Now we know the value of distance of angle SDE and line SE (1 AU). Using the information, using the trigonometry, you can know the value of SD or ED. If the value of the front angle becomes 1 arc second, the distance of the star will be 1 parseque. Now we are in the position to define 1 parsek. A parsec i.e. the distance at which the subtends 1 arcsecound facing 1 AU

The importance of parsec

In the field of astrophysics, the transsexual method is the most important phase of calibration in determining distance. Perlox measurement limit is 0.01 arcsecond by telescope based on Earth, which is not possible due to the precise measurement of the distance of stars over 100 paras. This boundary is due to the obscuration of the image of the Earth’s atmosphere. But the space station does not have this limit in front of the telescope. In space, the use of parsek, kiloparsec and megaparsake for measuring the distance of the objects of the distance.

Related words-

what’s in the distance, cosmic distance ladder, astronomical unit, trigonometric parallax, parallax angle, stellar parallax, parallax method, how do we measure astronomical distances.