On Earth, we can track the passage of time by seeing the Sun and Moon rise and set, or by counting the days, weeks, months, and years. To put it another way, we measure time by the Earth’s rotation and orbit around the Sun.
This yardstick of measurement vanishes after you depart the Earth. There is no such thing as day or night in space. As a result, there is no sense of weeks or years. The distances between the stars are so immense that it is difficult to comprehend. For measurements in space, our ordinary clocks and measuring instruments are completely useless. As a result, astronomers have devised a new unit for measuring distances in space. It is called the light year. Let us see more about Space and Time
What is a light year?
Sometimes we use a unit of time to express distance. For example you might call a friend, and tell him that you are ten minutes away from his house. You’re substituting the time it will take you to get there for the distance you are.
When astronomers calculate the distance to a star or galaxy, they use the same method. They use the light year. A light year is a measurement of how far a ray of light travels in a year. All light travels at the same speed across the Universe. However, the primary rationale for utilizing light years is that the distances we deal with in space are enormous. We quickly run into awkward quantities if we stick to km.
The beginning of Space and Time
Our concept of time starts with the time the Universe began. It is now believed that the Universe as we know it is the result of a gigantic explosion that is referred to as The Big Bang. Around 14 billion years ago, the entire Universe was contained within a tiny bubble the size of a pinhead. It was far hotter and denser than we could have imagined. Then, all of a sudden, it detonated. The Universe grew from the size of a single atom to the size of a galaxy in a fraction of a second. And it continued to grow at a phenomenal rate, and it continues to do so. The Big Bang was the beginning of time, space, and matter.
Time on different planets
We calculate time on the basis of the Earth’s rotation and its orbit around the Sun. But planets rotate, or spin at different speeds. Jupiter spins the fastest, while Mercury is the slowest. Therefore, the concept of a ‘day’ will differ from planet to planet. Similarly, we define a year as the length of time that the Earth takes to complete one revolution around the sun. However, other planets revolve around the Sun in different amounts of time. Thus, a ‘year’ on each planet is a different amount of time. Planets further away from the Sun have longer years than planets nearer the Sun. So, a year in Mars lasts 686.98 earth days, while Mercury’s year is just 87.96 Earth days.
Time difference between Jupiter and the Earth
Jupiter is 317.8 times bigger than the Earth. However, it spins at a much faster rate. Thus, its day is only 10 hours long, as compared to the 24 hours that make up our day. At the same time, Jupiter is much farther away from the Sun than the Earth is. This means that it will take much longer to complete one revolution of the Sun. So, while the Earth takes one year or 365 earth days to complete one revolution, Jupiter takes 12 Earth years to go around the Sun! In the same way, each of the planets in our solar system has days and years of different lengths. So, the concept of time varies from planet to planet.
Ancient concept of Time
For ancient cultures, concepts of time were related to the movement of the heavenly bodies. The Ancient Egyptians used sundials to calculate time based on the Sun.
Water clocks were used to keep track of time even at night, but they required manual upkeep to keep the water flowing. Hourglasses filled with sand could also measure time, but only for a limited period. As long back as 6000 years ago, the Moon was utilized to determine time. Many societies have adopted lunar calendars since then. However, the lunar calendar proved quite confusing, and SO many cultures adopted the solar calendar which was based on the Earth’s revolution around the Sun. The Incas, Mayan, and other Native American cultures also had their own concepts of time.
Time in Greek mythology
Time was described in two ways by the Ancient Greeks. The first was Chronos which referred to chronological time. Chronological time arranges events in the order in which they our. Chronos was time that could be measured in seconds, minutes, hours, days, weeks months and years. The second word for time was Kairos. It referred to divine time. Kairos referred to moments – to the right moment, the opportune moment, the moment that changes destiny.
Chronos was portrayed as an elderly guy with a long grey beard who wielded a scythe and an hourglass. Kairos, on the other hand, was always depicted as a young man, lithe and skilled with his hands. His statues can be found all throughout the Greek peninsula.