165,000 light years. Distances in space. Astronomical unit, light year and parsec
As you know, to measure the distances from the Sun to the planets, as well as between the planets, scientists came up with an astronomical unit. What is light year?
First of all, it should be noted that a light year is also a unit of measurement adopted in astronomy, but not of time (as it may seem, judging by the meaning of the word “year”), but of distance.
What is a light year
When scientists were able to calculate the distances to the nearest stars, it became obvious that in the stellar world the astronomical unit was inconvenient for use. Let's say for starters that the distance from the Sun to the nearest star is about 4.5 light years. This means that the light from our Sun to the nearest star (it is called, by the way, Proxima Centauri) flies 4.5 years! How big is this distance? We will not bore anyone with mathematics, we will only note that in a second particles of light fly 300,000 kilometers. That is, if you send a signal with a flashlight towards the Moon, this light will be seen there in less than a second and a half. Light travels from the Sun to the Earth in 8.5 minutes. And how much then do the rays of light fly by in a year?
Let's just say: a light year is about 10 trillion kilometers(a trillion is a one followed by twelve zeros). More precisely, 9,460,730,472,581 kilometers. If recalculated in astronomical units, then it will be approximately 67,000. And this is only to the nearest star!
It is clear that in the world of stars and galaxies the astronomical unit is not suitable for measurements. It is easier to operate in calculations with light years.
Applicability in the stellar world
For example, the distance from Earth to the brightest star in the sky, Sirius, is 8 light years. And the distance from the Sun to the North Star is about 600 light years. That is, the light from us gets there for 600 years. It will be approximately 40 million astronomical units. For comparison, we point out that the size (diameter) of our Galaxy - the Milky Way - is about 100,000 light years. Our closest neighbor, a spiral galaxy called the Andromeda Nebula, is 2.52 million light-years away from Earth. It is very inconvenient to state this in astronomical units. But there are objects in the Universe that are 15 billion light-years distant from us. Thus, the radius of the observable universe is 13.77 billion light years. And the full Universe, as you know, extends beyond the observable part.
By the way, the diameter of the observable Universe is not at all 2 times larger than the radius, as one might think. The point is that space expands over time. Those distant objects that emitted light 13.77 billion years ago flew even further away from us. Today they are more than 46.5 billion light-years away. Doubling that, we get 93 billion light years. This is the true diameter of the observable universe. So the size of the part of space that is being observed (and which is also called the Metagalaxy) is increasing all the time.
It makes no sense to measure such distances in kilometers or astronomical units. To be honest, light years don't quite fit here either. But people haven't come up with anything better yet. The numbers are so huge that only a computer can handle them.
Definition and essence of the light year
Thus, a light year (st. g.) is a unit of length, not time, which is the distance traveled by a sunbeam in a year, that is, in 365 days. This unit of measurement is very convenient for its clarity. It allows you to answer the question, after what period of time you can expect a response if you send an electromagnetic message to a certain star. And if this period is too long (for example, it is a thousand years), then there is no point in such actions.
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1 kilometer [km] = 1.0570008340247E-13 light year [St. G.]
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More about length and distance
General information
Length is the largest measurement of the body. In three dimensions, length is usually measured horizontally.
Distance is a measure of how far two bodies are from each other.
Distance and length measurement
Distance and length units
In the SI system, length is measured in meters. Derived quantities such as kilometer (1000 meters) and centimeter (1/100 meter) are also widely used in the metric system. In countries that do not use the metric system, such as the US and the UK, units such as inches, feet, and miles are used.
Distance in physics and biology
In biology and physics, lengths are often measured much less than one millimeter. For this, a special value, a micrometer, has been adopted. One micrometer is equal to 1×10⁻⁶ meters. In biology, micrometers measure the size of microorganisms and cells, and in physics, the length of infrared electromagnetic radiation. A micrometer is also called a micron and sometimes, especially in English literature, is denoted by the Greek letter µ. Other derivatives of the meter are also widely used: nanometers (1×10⁻⁹ meters), picometers (1×10⁻¹² meters), femtometers (1×10⁻¹⁵ meters), and attometers (1×10⁻¹⁸ meters).
Distance in navigation
Shipping uses nautical miles. One nautical mile is equal to 1852 meters. Initially, it was measured as an arc of one minute along the meridian, that is, 1/(60 × 180) of the meridian. This made latitude calculations easier, since 60 nautical miles equaled one degree of latitude. When distance is measured in nautical miles, speed is often measured in nautical knots. One knot is equal to one nautical mile per hour.
distance in astronomy
In astronomy, long distances are measured, so special quantities are adopted to facilitate calculations.
astronomical unit(au, au) is equal to 149,597,870,700 meters. The value of one astronomical unit is a constant, that is, a constant value. It is generally accepted that the Earth is located at a distance of one astronomical unit from the Sun.
Light year equals 10,000,000,000,000 or 10¹³ kilometers. This is the distance that light travels in a vacuum in one Julian year. This value is used in popular science literature more often than in physics and astronomy.
Parsec approximately equal to 30,856,775,814,671,900 meters or approximately 3.09 × 10¹³ kilometers. One parsec is the distance from the Sun to another astronomical object, such as a planet, star, moon, or asteroid, with an angle of one arcsecond. One arc second is 1/3600 of a degree, or about 4.8481368 mrad in radians. Parsec can be calculated using parallax - the effect of a visible change in the position of the body, depending on the point of observation. During measurements, a segment E1A2 (in the illustration) is laid from the Earth (point E1) to a star or other astronomical object (point A2). Six months later, when the Sun is on the other side of the Earth, a new segment E2A1 is drawn from the new position of the Earth (point E2) to the new position in space of the same astronomical object (point A1). In this case, the Sun will be at the intersection of these two segments, at point S. The length of each of the segments E1S and E2S is equal to one astronomical unit. If we postpone the segment through the point S, perpendicular to E1E2, it will pass through the intersection point of the segments E1A2 and E2A1, I. The distance from the Sun to point I is the SI segment, it is equal to one parsec when the angle between the segments A1I and A2I is two arcseconds.
On the image:
- A1, A2: apparent star position
- E1, E2: Earth position
- S: position of the sun
- I: point of intersection
- IS = 1 parsec
- ∠P or ∠XIA2: parallax angle
- ∠P = 1 arc second
Other units
League- an obsolete unit of length used earlier in many countries. It is still used in some places, such as the Yucatan Peninsula and rural areas of Mexico. This is the distance a person walks in an hour. Marine League - three nautical miles, approximately 5.6 kilometers. Lie - a unit approximately equal to the league. In English, both leagues and leagues are called the same, league. In literature, the league is sometimes found in the title of books, such as "20,000 Leagues Under the Sea" - the famous novel by Jules Verne.
Elbow- an old value equal to the distance from the tip of the middle finger to the elbow. This value was widespread in the ancient world, in the Middle Ages, and until modern times.
Yard used in the British imperial system and is equal to three feet or 0.9144 meters. In some countries, such as Canada, where the metric system is adopted, yards are used to measure the fabric and length of swimming pools and sports fields and grounds, such as golf and football courses.
Meter Definition
The definition of the meter has changed several times. The meter was originally defined as 1/10,000,000 of the distance from the North Pole to the equator. Later, the meter was equal to the length of the platinum-iridium standard. Later, the meter was equated to the wavelength of the orange line of the electromagnetic spectrum of the krypton atom ⁸⁶Kr in vacuum, multiplied by 1,650,763.73. Today, a meter is defined as the distance traveled by light in a vacuum in 1/299,792,458 of a second.
Computing
In geometry, the distance between two points, A and B, with coordinates A(x₁, y₁) and B(x₂, y₂) is calculated by the formula:
and within a few minutes you will receive an answer.Calculations for converting units in the converter " Length and distance converter' are performed using the functions of unitconversion.org .
Do you know why astronomers don't use the light year to calculate distances to distant objects in space?
A light year is a non-systemic unit for measuring distances in outer space. It is ubiquitous in popular books and textbooks on astronomy. However, in professional astrophysics, this figure is used extremely rarely and often to determine distances to nearby objects in space. The reason for this is simple: if you determine the distance in light years to distant objects in the Universe, the number will be so huge that it will be impractical and inconvenient to use it for physical and mathematical calculations. Therefore, instead of a light year, professional astronomy uses such a unit of measurement as , which is much more convenient to operate when performing complex mathematical calculations.
Definition of the term
We can find the definition of the term "light year" in any astronomy textbook. A light year is the distance that a ray of light travels in one Earth year. Such a definition may satisfy the amateur, but the cosmologist will find it incomplete. He will notice that a light year is not just the distance that light travels in a year, but the distance that a beam of light travels in 365.25 Earth days in vacuum, without being affected by magnetic fields.
A light year is 9.46 trillion kilometers. This is the distance a ray of light travels in a year. But how did astronomers achieve such an accurate determination of the ray path? We will talk about this below.
How is the speed of light determined?
In ancient times, it was believed that light propagates in the universe instantly. However, beginning in the seventeenth century, scholars began to doubt this. Galileo was the first to doubt the above proposed statement. It was he who tried to determine the time during which a ray of light travels a distance of 8 km. But due to the fact that such a distance was negligible for such a value as the speed of light, the experiment ended in failure.
The first major shift in this issue was the observation of the famous Danish astronomer Olaf Römer. In 1676, he noticed the difference in the time of an eclipse depending on the approach and removal of the Earth to them in outer space. Roemer successfully connected this observation with the fact that the farther the Earth moves away from, the more time it takes for the light reflected from them to travel the distance to our planet.
Roemer caught the essence of this fact exactly, but he did not succeed in calculating the reliable value of the speed of light. His calculations were wrong, because in the seventeenth century he could not have accurate data on the distance from the Earth to other planets in the solar system. These data were determined somewhat later.
Further advances in research and determination of the light year
In 1728, the English astronomer James Bradley, who discovered the effect of stellar aberration, was the first to calculate the approximate speed of light. He determined its value at 301 thousand km / s. But this value was inaccurate. More advanced methods for calculating the speed of light were produced irrespective of cosmic bodies - on Earth.
Observations of the speed of light in vacuum using a rotating wheel and a mirror were made by A. Fizeau and L. Foucault, respectively. With their help, physicists managed to get closer to the real value of this quantity.
Accurate speed of light
Scientists managed to determine the exact speed of light only in the last century. Based on Maxwell's theory of electromagnetism, using modern laser technology and calculations, corrected for the refractive index of the ray flux in air, scientists were able to calculate the exact value of the speed of light 299,792.458 km/s. This value is still used by astronomers. Further, to determine the light day, month and year was already a matter of technology. By simple calculations, scientists got the figure of 9.46 trillion kilometers - that is how long it would take for a beam of light to fly around the length of the earth's orbit.
For their calculations, astronomers use special units of measurement that are not always clear to ordinary people. It is understandable, because if cosmic distances were measured in kilometers, then the number of zeros would ripple in the eyes. Therefore, to measure cosmic distances, it is customary to use much larger quantities: an astronomical unit, a light year, and a parsec.
Quite often used to indicate distances within our own solar system. If you can still express it in kilometers (384,000 km), then the closest way to Pluto is about 4,250 million km, and this will already be difficult to understand. For such distances, it is time to use the astronomical unit (AU), equal to the average distance from the earth's surface to the Sun. In other words, 1 a.u. 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 can be 50 AU, this is much easier to imagine.
The next largest is the light year. Although the word “year” is present, you should not think that it is about time. One light year is 63,240 AU. This is the path that a ray of light travels in 1 year. Astronomers have calculated that it takes more than 10 billion years for a beam of light to reach us from the farthest corners of the universe. To imagine this gigantic distance, let's write it down in kilometers: 950000000000000000000000. Ninety-five billion trillion habitual kilometers.
The fact that light does not propagate instantly, but at a certain speed, scientists began to guess since 1676. It was at this time that a Danish astronomer named Ole Römer noticed that the eclipses of one of Jupiter's moons began to lag, and this happened precisely when the Earth was heading in its orbit towards the opposite side of the Sun, the opposite of where Jupiter was. Some time passed, the Earth began to return back, and the eclipses again began to approach the previous schedule.
Thus, about 17 minutes of time difference was noted. From this observation, it was concluded that it took 17 minutes for light to travel a distance the length of the diameter of the Earth's orbit. Since it has been proven that the diameter of the orbit is approximately 186 million miles (now this constant is 939,120,000 km), it turned out that a beam of light moves 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 a light year is, using a different method, the final result was obtained: 186,284 miles in 1 second (about 300 km / s). Now, if we calculate the number of seconds in a year and multiply by this number, we get that a light year is 5,880,000,000,000 miles long, which corresponds to 9,460,730,472,580.8 km.
For practical purposes, astronomers often use the unit of distance known as the parsec. It is equal to the displacement of the star against the background of other celestial bodies by 1 "" when the observer is displaced by 1 radius
In order to understand the meaning of the concept of "light year", you first need to remember the school physics course, especially the section that concerns the speed of light. So, the speed of light in vacuum, where it is not affected by various factors, such as gravitational and magnetic fields, suspended particles, refraction of a transparent medium, and so on, is 299,792.5 kilometers per second. It must be understood that in this case, light means those perceived by human vision.
Less well-known distance units are the light-month, week, day, hour, minute, and second.Long enough light was considered an infinite quantity, and the first person to calculate the approximate speed of light rays in a vacuum was the astronomer Olaf Roemer in the middle of the 17th century. Of course, his data were very approximate, but the very fact of determining the final value of the speed is important. In 1970, the speed of light was determined to within one meter per second. More accurate results have not been achieved so far, as there were problems with the error of the meter standard.
Light year and other distances
Since the distances in are huge, measuring them in customary units would be irrational and inconvenient. Based on these considerations, a special light year was introduced, that is, the distance that light travels in the so-called Julian year (equal to 365.25 days). Considering that each day contains 86,400 seconds, it can be calculated that in a year a ray of light covers a distance of several more than 9.4 kilometers. This value seems huge, however, for example, the distance to the nearest star to the Earth, Proxima Centauri, is 4.2 years, and the diameter of the Milky Way galaxy exceeds 100,000 light years, that is, those visual observations that can be made now display a picture that existed about hundreds of thousands of years ago.
A beam of light covers the distance from the Earth to the Moon in about a second, but sunlight reaches our planet for more than eight minutes.
In professional astrophysics, the concept of a light year is rarely used. Scientists mainly operate with units such as the parsec and the astronomical unit. A parsec is the distance to an imaginary point from which the radius of the Earth's orbit is seen at an angle of one arc second (1/3600 of a degree). The average radius of the orbit, that is, the distance from the Earth to the Sun, is called the astronomical unit. A parsec is about 3 light years or 30.8 trillion kilometers. An astronomical unit is approximately equal to 149.6 million kilometers.