It is all about Reference Frame
Time Seeds of Universe – 2
Let the mind slowly absorb the information and put them into context, as it is not merely about numbers.The revolution of many masses around each other, floating in the space at a speed that humans have not experienced on their home planet. The highest speed I have achieved on a highway is 120km/hr (33m/sec), and that was only for a few minutes. Earth’s revolution speed is close to 30km/s, which is almost 10,000 times faster than the speed I could achieve in my lifetime.
Speed of Earth is beyond my imagination to comprehend that we all are together with the Earth. continuously moving at this speed. It never stops, even for a nano second. While we are briefly existing on this earth in stillness, nothing is truly still. During our entire lifetime, which is just a blink in the timeline of universe, we can only perceive as much as our mind allows. This mind itself is infinitely vast and we know very little of its wilderness. Is the mind is a mini model of the universe? Such thoughts make my head spin instead of making it still!
Axial Tilt and Precession
Moving on from revolution, I delve into the concept of axial tilt. What is the axis of Earth? There is no such physical axis around which earth rotates. In fact, because the Earth rotates, it has an axis. If the Earth were static, there would be no axis! But then, again, nothing is static, so everything that moves has an axis.
The Earth rotates around its axis, giving us day and night. It is like a game of peek-a-boo game with the Sun, rotating once in every 23.9 hours. However, this speed is not constant like other speeds, it is slowing down. The rotation speed was faster in the past, resulting in slower days, and it will be slower in the future, leading to longer days. These changes occur in milliseconds over hundreds of years, so only precise atomic clocks can detect the subtle variation, and the time adjustments can be made accordingly. But the real wonder is the axial tilt, which makes life on Earth so beautiful and diverse.
From the perspective of an observer outside the solar system, Earth’s axis of rotation is tilted 23.4 degrees with respect to the plane of Earth’s orbit around the Sun. This tilt causes our yearly cycle of seasons because different points on earth receive different amount of sunlight throughout the solar year, following a set rhythm. During part of the year when the northern hemisphere is tilted toward the Sun, and the southern hemisphere is tilted away, solar heating is greater in the north producing summer there. Less direct solar heating produces winter in the south. Six months later, the situation is reversed. When spring and fall begin, both hemispheres receive roughly equal amounts of heat from the Sun. However, this axial tilt is not constant and we should expect seasonal patterns to remain the same forever. Patterns exist in the world but only within the frame of space and time. There is a pattern in changing pattern!
Earth’s axial tilt actually oscillates between 22.1 and 24.5 degrees. The changing obliquity angle is a result of Earth’s axis wobbles around itself, a motion known as axial precession. This precession of Earth’s rotational axis is due to the tidal force raised on Earth by the gravity of the Moon and Sun. Too many motions to factor in!
A Cycle of 26000 years
The reference frame of an observer outside the solar system, the positions of the south and north celestial poles of Earth appear to move in circles completing one circuit in approximately 26,000 years. For an observer on Earth, the space-fixed backdrop of stars changes over this cycle. The constellations visible in past are not visible now and the constellations we see today in the sky will not be visible in the future. Earth’s precession also causes shift in the equinoxes and consequently will shift the seasons to different months in year a year. However, these shifts occur slowly over a few thousand years and we will not be able to witness these changes in our lifetime or this body forms. But then again, who knows? We have always been there, floating in the vast universe in different manifestations!
Similar to earth, all the bodies- planets and their moons have their own tilt with respect to their plane of revolution around the larger bodies.
I am totally fascinated watching the axial tilt, precession , resembling a gyroscope in visuals presentation. During high school days, I used to spin a wooden spinning top (लट्टू ) to understand different types of motions, as we did not have access to the internet. In the book “Classical Mechanics” by Halliday Resnick, the chapter introduced the concept of gyration but reserved the equations for the next chapter, which was not in our syllabus. At that, I was not inclined to go beyond the syllabus.
Now, I am learning about precession and how our Earth’s precession cycle spans 26,000 years, causing changes in our view of the sky changes. Our reference stars, constellations , which guide humans, were different 10,000 years ago, and will change in the next 10,000 years. The Polaris / North Star of today will not be the North Star of tomorrow due to precession; and that tomorrow is just several thousands years from now. Another star will act as the guiding star to define the North. Currently, we have a significantly bright star directly above the North Pole that is visible to the naked eyes, allowing anyone to locate the North. It will not be visible to the naked eyes after a few thousand years. Humans need to find another another North Star, if we do not become extinct by then.
Do we have a similar Pole star in the South? For now, there is no pole star for theSouth Pole, as none of the stars are visible to the naked eye. However, Sirius, the brightest star in the current night sky, will become the Southern Pole star in roughly 90,000 years. To be a pole star for human, a star must be visible to the naked eye. Who knows about star gazing and timekeeping methods of other creatures such as birds, fishes, animals and trees?
What causes such rotations, revolutions, tilts and precessions? These are the motions we have been able to identify and define for different planets. What about existence of many invisible forces within and outside celestial bodies that may have an impact on these motions? What all unknown variables exist? And the bigger question is, WHY?
I spent days wondering about the minuscule frame within which we perceive reality. All the festivals that occur year after year condition our minds to associate them with a certain time of the year, season, and symbols such as flowers, harvest, food, rain, snow. All of this will change in the next few thousand years! Every time I learn something new, it further emphasises the insignificance of the self. If the earth is that tiny spec of dust in this vast universe, how small are we in that spec of dust. However, don’t we contain the entire universe of silence and noise, light and darkness within us!
I am in complete awe of the wonders of this universe, its infinity, its vastness, and the fact that we may know very little of all that is yet to be known.
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Time Seeds of Universe is a series on understanding time. ‘Time Seeds of Universe: Its about Reference Frame‘ is part 2 in this series. Following are the link to other blogs of this series :
Time Seeds of Universe- 1 : A Journey of Self-Discovery
Time Seeds of Universe – 3 : A Sphere with Infinite Radius
Time Seeds of Universe- 4: Path, Light and Shadows
Time Seeds of Universe – 5: Quest for Salvation in the Wonders of Nature
Image Credit: By NASA, Mysid – Vectorized by Mysid in Inkscape after a NASA Earth Observatory image in Milutin Milankovitch Precession., Public Domain, https://commons.wikimedia.org/w/index.php?curid=3993432
