What is a Light-year?
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Definition and meaning
Light Year is the distance that light travels in a year with the speed of light which is 3×108msec−1. A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km.
Significance and examples
A light-year is a unit to measure distance. It is defined as the distance that a beam of light can travel in one year. One light-year is equal to 6 trillion miles or 9.5 trillion kilometers or 63,241 astronomical units. No object in the universe travels faster than light itself.
Take the example of Proxima Centauri, the nearest star beyond the sun. You could say that it's about 24,900,000,000,000 miles away or even display the distance as a tidy 4.24 light-years. So it is assumed that most of the stars you see at night lie within a few hundred light-years of Earth and the nearest star to the earth is about 4.3 light-years away.
More About the Topic
A light-year is a unit to measure distance. It is defined as the distance that a beam of light can travel in one year. One light-year is equal to 6 trillion miles or 9.5 trillion kilometers or 63,241 astronomical units. No object in the universe travels faster than light. Light moves in space at a speed of 300 million meters per second. Astronomers use the light-year to measure enormous distances in space, like how far the stars, planets, and galaxies are. For example, after the Sun, the next closest star to Earth is 4.3 light-years away.
Light travels large distances very quickly in space. For example, it takes 8.53 minutes to travel from the Sun to the Earth. There is a unit even larger than a light year, called a parsec. It is about 3.26 light-years. Parsec has made it easier for astronomers to measure even larger distances. Now when we know what a light-year is, let us find the dimension of the light-year. However, before starting with our findings, we need to understand the significance of dimensions.
Significance of Dimensions
Understanding dimensions helps us in studying the nature of physical quantities mathematically. The fundamental concept of dimensions is that we can add or subtract only those quantities which have the same dimensions. Also, two physical quantities can be equal only if they have the same dimensions.
Dimension of a Light-Year
Through our readings above, we conferred that light-year is how quickly light can travel in space. This means we are talking about the distance that light covers between two astronomical objects. As we know the dimension of length or distance is [M0L1T0]. Similarly, the dimension of a light-year is [M0L1T0].
Now, if we look at the value of one light year in terms of Kms, miles, and Astronomical units, these are all units of distances, and also these all have dimensions of length. So, whatever units we take, the dimension of the light-year remains the same. Let us take a look at the values of the light-year in different systems of units
Conversions
As we know that light-year is a distance travelled by astronomical objects. In the macrocosm measurements, i.e., measuring very large distances, we have two more units for the same.
Some Important Macrocosm Units
Let us discuss some important practical units to measure astronomical distances.
1. Astronomical Unit
It is the average distance of the center of the Sun from the center of the Earth.
The value of one astronomical unit or 1 A.U is 1.496 x 1011m~ 1.5 x 1011m.
2. Parsec
It is another unit of measurement of very large distances in space. Here, parsec represents Parallactic seconds. Parsec is the distance at which an arc 1 AU subtends an angle of 10.
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We know that 1 AU = 1.496 x 1011 m
And, Ө = 1 sec or 160
160 s =160×60
160×60 degrees.
So, 1 sec = 160×60
160×60×π 180
π180 radian
We know that r =lӨ
where, l = 1 AU and 1 sec =160×60
160×60×π180
π180
So, 1 parsec =1AU1sec
1AU1sec= 1.496×1011160×60×π180
1.496×1011160×60×π180
On solving, we get,
1 parsec = 3.1 x 1016 m
Relationship Between ly, AU, and parsec
Let us derive the relation between these three units.
1. The relation between ly and AU
We know that 1 ly = 9.4607 x 1015 m
1 AU = 1.5 x 1011 m
Now,1ly1AU
1ly1AU= 9.4607 x 1015 m / 1.5 x 1011 m On solving, we get,
2.The relationship between parsec and ly:
We know that 1 parsec = 3.1 x 1016 m and
ly = 9.4607 x 1015 m
Now, 1parsec / 1ly = 3.1 x 1016m / 9.4607 x 1015 m
On solving, we get,
This is how we can derive the relationship between various astronomical units.
FAQs on Dimensions of Light Year
1. Calculate the number of Astronomical Units in one meter.
We know that 1 AU = 1.5 x 1011m
Or, 1.5 x 1011m = 1 AU
So, 1 m = 1/1.5 x 1011 AU
On solving, we get,
1 AU = 6.67 x 10-12m.
2. Calculate the number of Light-years in one meter.
We know that 1 ly = 9.4607 x 1015 m
So, 1 m = 1/9.4607 x 1015ly
On solving, we get,
1 ly = 1.057 x 10-16ly
3. Derive the value for one Light-year.
We know that the speed of light = 3 x 108ms-1
Length of Earth year = 365 days, and
365 days = 365 x 24 hours = 365 x 24 x 60 minutes = 365 x 24 x 60 x 60 seconds
On solving, we get the length of Earth year = 3.15 x 107 s.
∴ Distance = Speed x time = 3 x 108ms-1 x 3.15 x 107 s
So, 1 light-year = 9.45 x 1015m.
4. Define Light-year in days.
According to the International Astronomical Units, a light-year is a distance that light travels in a vacuum in one Julain year, i.e., 365.25 days.
5. What is the importance of understanding dimensions in physics?
The necessity of Dimensional Equations and their importance is to find the dimension of constants in any given relationship. One form of the unit can be converted into another form of unit. And also the accuracy of an equation can be found and verified properly. Every student should understand and learn the concept of finding dimensions in physics. It is clearly explained on the Vedantu website by expert teachers for better clarity.
6. What are the fundamental dimensions taught in physics subjects?
Physics subject deals with seven primary dimensions on the whole. Primary dimensions sometimes called basic dimensions are defined as independent or fundamental dimensions in physics, from which other various dimensions can be obtained. The primary dimensions dealt with are mass, length, time, temperature, electric current, amount of light, and amount of matter. Students should keep track of all dimensions in the physics subject and learn the concepts very well in order to score well.
7. What are the advantages of dimensional analysis?
The main advantage of dimensional analysis in the physics subject helps in analyzing any problem in detail so that it reduces the number of variables in the problem by combining dimensional variables to form non-dimensional parameters. By far the simplest and most desirable method in the analysis of any fluid problem is that of direct mathematical solution. In physics, analyzing and understanding the dimensions used in every concept and research is very important to find out the solutions easily.
8. What is the importance of dimensional analysis and what are its limitations?
Dimensions have more uses and effects but still they have some limitations as well. The limitation of Dimensional Analysis is that it doesn't give information about the dimensional constant. The formula involved in physics concepts containing trigonometric function, exponential functions, logarithmic function, etc. cannot be derived. It gives no information about whether a physical quantity is a scalar or vector unit.
9. What is the most important significance of the light-year?
A light-year is denoted as the unit of distance in physics. It is the total amount of distance that the light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So in one year, it can travel about 10 trillion km. A light-year equals about 9.46073 × 1012 km (5.87863 × 1012 miles), or 63,241 astronomical units. About 3.262 light-years equals one parsec.
