The Joint Entrance Examination(JEE) is a form of engineering entrance assessment conducted for students to help them for admission to various engineering colleges located in India. It is constituted by two different examinations like the JEE Main and the JEE Advanced. JEE and IIT are not the same terms but are definitely interconnected to each other having something in common. IITs (Indian Institute of Technology) are the top engineering colleges found in every country whereas JEE is an entrance exam for getting admission in these top IITs. IIT JEE is generally called the entrance exam for admission in top engineering colleges in any part of the country.
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
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.
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
So, 1 sec = 160×60
We know that r =lӨ
where, l = 1 AU and 1 sec =160×60
So, 1 parsec =1AU1sec
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
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.