What is a Light Year?
Light - Year is the unit of distance denoted by a symbol ‘ly’. It is the distance traveled by a light in one year.
As defined by the International Astronomical Union, it is the distance traveled by a light photon in vacuum in one Julian year.
What is Julian Year?
As the name suggests, it would appear that the Julian year may correspond to the years in a Julian calendar or maybe a way to measure or define a year. But, a Julian year is not an unit of measurement rather it is a SI Unit in astronomy. A Julian Year has 365.25 days.
In astrophysics, the term light - year term is often used to measure the distance between two astronomical objects. Such as the distance between the earth and the sun can be measured in terms of light - year.
The value of light - year in S.I. (metrics) is equivalent to :
Light Year
Light-year or lightyear is the distance traveled by light in one Earth year.
A light year is a way of measuring distance just like an inch, meter, kilometer, or a mile. That word ’year’ in ‘light year’ is a unit of time. However, light year is a measurement of distance.
Light Year is a Unit of
Light year (ly) is a unit of length or distance. It is the length of distance a light covers in one year.
One Light Year Distance
One light year distance is equal to 9.461e+15 meters (m).
1 Light Year in Km
1 light year in km is equivalent to 9.4607 × 10¹² Km.
One Light Year in Miles
In Imperial and US units, one light year is equivalent to 5.878 trillion miles or 5.878 × 10¹² miles which is equivalent to 9.5 trillion km.
1 Light Year in Days
As defined by the International Astronomical units (IAU), A light year is the distance traveled by light in a vacuum in one Julian year is equal to 365.25 days.
Therefore, one light - year = 365.25 days.
1 au in light years
1 astronomical unit or au is equal to
Distance From Earth to Sun in Light Years
Earth is the third planet from the Sun and is considered the only astronomical body known to harbor (support) life.
In light years, the current distance of Earth from the Sun is:
How Many Kilometers is One Astronomical Unit au?
The distance of the earth from the sun is about 149.6 million km.
1 astronomical unit or au is equivalent to 1.496e+8 kilometers.
One Light - Year is Equal to How Many Years?
Basically, in a vacuum, the light travels at a speed of 1,079,252,849 km/h.
There are 8766 hours in a year.
Since, Distance = Speed x Time = s x t…(1)
Therefore, to find the distance of a light year, we need to multiply this speed by the number of hours in a year.
Given, s = 1,079,252,849 km/h and t = 8766 hours
Putting the value of s and t in eq(1), we get:
Distance = 1,079,252,849 x 8766
Hence, one light year = 5,878,625,370,000 miles.
Planets distances from the Sun
The distance light travels in a year is called the light year. Since the galaxy is vast, it is difficult to measure the distances in conventional ways. A light year was invented in order to measure such a large distance with ease. Given below is a table which shows the distance of each planet from the sun in light years.
What are Light Years Used for?
Measuring the astronomical distances, it becomes quite impossible and extremely cumbersome to measure these huge distances in miles or kilometers.
For example, in our cosmic neighborhood, the closest star-forming region to us is the Orion Nebula which is at a short distance of 7,861,000,000,000,000 miles. We can rewrite this in light - years as 1,300 light years away.
Therefore, measuring the astronomical distances in light years helps astronomers to determine how far back in time they are viewing.
Since light takes time to travel to our eyes which means that everything we view in the sky at night has already happened.
In other words, when we observe something one light year away, we see it as it appeared exactly one year ago.
As we can see the nearest spiral galaxy, the Andromeda galaxy is 2.5 million light years away. It means this galaxy appeared 2.5 million years ago.
Do You Know?
Light travels at a velocity of 3000 Km each second.
In a vacuum, it moves at a speed of 670,616,629 mph or 1079,252,849 km/h.
Sometimes astronomers use a unit ‘Parsecs or pc’ as an alternative to light years.
The distance between the galaxy and the earth is 65 million (mi) light years or 382 quintillions (10¹² million) miles.
The nearest star to our sun is Proxima Centauri which is 4.2 light years away.
In one year, light can cover a distance of about 10 trillion kilometers or 10⁶ Km.
In astronomical units (au), one light year is equivalent to 63241 au or 0.3066 pc where au stands for astronomical unit and pc for Parsecs.
Conclusion
This is how a light year is calculated in astrophysics. It is done to measure the huge distance between astronomical bodies. Focus on the formula to calculate the distance represented by one light year and the information related to it.
FAQs on Value of One Light Year
1. Who Introduced Light Year?
In 1838, the German astronomer Friedrich Wilhelm Bessel was the first to bring the concept of light year. He used the light year as a unit of measurement in astronomy to measure the astronomical distances. He measured the distance separating us from the binary star 61 Cygni that was equivalent to 10.3 light years. This distance came out to be 660,000 times the Earth's orbital radius.
2. Is the Sun a Light Year Away?
The sun is 151.96 million kilometers away from the Earth.
Light travels 186,282 miles per second
A lightyear is a distance that is equal to speed x time.
= 186,282 miles per second x 60 seconds per minute x 60 minutes per hour x 24 hours
per day x 365 days per year.
On solving we get one light - year = 5,874,589,152,000 miles.
Therefore, the Sun is approximately 93,000,000 miles from Earth.
3. How Fast Does Light Travel?
31 light years is equal to 279 trillion kilometers or 18,60,000 AU.
For this, we need a vehicle (i.e., approximately not less than 1/1000th the speed of light to transport to this mammoth distance.
Therefore, it would take a minimum of 31000 years to travel 31 light years.
4. What is parallax?
Parallax is one of the methods to measure distances between two heavenly planets. This can be understood with the help of the given example below:
If we want to measure the distance between the earth and any other planet (say P), we will use the parallax method. The first step would be to mark two points, A and B, on two places on the surface of the earth from where that planet (P) is seen. b can be the distance between the two points A and B and d can be the distance between the two planets. Then, we will find the measure of the parallax angle which is formed by the two distances AP and BP. Let the angle be θ.
Formula-
Sinθ = AB/AP
= b/d
So, d = b/θ
We can easily find the distance between two heavenly bodies by the parallax method, however, when the distance becomes too large, then the method cannot be used as the angle would become too small to measure. Hence, the answers would not be accurate.
