How Long is a Galactic Year?

Before knowing how long is a Galactic year, let us first understand the concept of year and Galactic year. 



What is a Year?

A year is the length of time it takes for a planet or asteroid to complete a full orbit of its star. As we already know that the Earth orbits the Sun which is its star. The Earth solar year is 365 days or 366 every four years.
Mars has its own year and it is referred as a Martian Year and that is 687 days. The further we move from the Sun, the longer that object's year get. Pluto, which is not a planet now, has the longest year of the main solar system objects. Pluto's year is 248 Earth years.
Before we deeper, here is an interesting fact, the planet Venus takes 224.65 days to orbit the Sun and is about the same size as the Earth. The time it takes to complete a day is longer than it takes to orbit the Sun. It also rotates in the opposite direction to the Earth.


What is the Galactic Year?

So we all knows that the Earth orbits around the Sun, taking one year to complete a full orbit. But, the Sun - in fact, our whole Solar System orbits the Supermassive Black Hole that is at the centre of our galaxy, the Milky Way. We are moving at an average velocity of 828,000 km/hr. But even at that high speed, it still takes 225 to 250 million years to complete one orbit around the Milky Way.
The duration of time required for the Sun to complete a orbit once around the center of the Milky Way Galaxy is called Galactic Year, also known as a cosmic year.
The Milky Way is a barred spiral galaxy having a diameter of around 150,000 to 200,000 light-years. It contains somewhere between 150 to 400 billion stars and an estimated 100 billion planets.
The Sun and the rest of our solar system, is located near the Orion arm, between two major arms - Perseus and Sagittarius. The Sun is located at a distance of around 28,000 light-years from the Galactic Center.
Since the Earth is estimated to be 4.543 billion years old, that means it has traveled around the Milky Way, along with the Sun, multiple times.  

How Long is a Galactic Year?

The time it takes to complete a full orbit of the galaxy is about 225 - 250 million Earth years. 
250 Million Years ago was the Jurassic Period was just beginning on Earth. It lasted approximately 56 million years, starting at the end of the Triassic Period, around 201.3 million years ago and ending at the beginning of the Cretaceous Period, about 145.5 million years ago and extended to the beginning of the Paleogene Period about 65.5 million years ago. The period between 65 million years ago and today is called the Cenozoic Period. Towards the end of this period, around 320,000 years ago, Homo sapiens first appeared. 

In other words, if we were to measure time by this galactic "clock," Earth would be about 16 years old in galactic or cosmic years, the sun would have formed about 20 years ago and the universe would be just about 60 years old. 



The End Notes

If we turned the time back one Galactic Year, Earth would be much different, no Internet, no Mobiles, not even humans could be found orbiting the Earth. That's all in this. I hope you liked it. Please comment your views and suggestions on this. 
Thanks for reading! 


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