It’s Diwali today.
The festival of light.
Which to an astronomer sounds like a wonderful thing to celebrate.
The triumph of light is a key moment in the evolution of the Universe, the evolution of matter and the evolution of Life.
Light defines our knowledge, our existence, the limits of our universe and is the ultimate speed limit. Light sets out the edge of our observable Universe, Light in many forms shows us much of what we know of the Sky above and all of that is bound up in the unbreakable 299,792,458 meters per second.
In the story of the Universe as we understand it today, light appears and illuminates the darkness of the Universe about 300,000 years after the event we call Big Bang. The ever expanding cosmos that until that point had been an impenetrable soup of photons, electrons, and protons cooled sufficiently to allow the formation of hydrogen atoms and suddenly light, so long imprisoned was released.
We see this still in the Cosmic Microwave Background Radiation, stretched and cooled and invisible to our eyes right now the first light is still escaping across the universe and is all around us. Discovered by accident in 1964, though predicted many years before the Universe has a gentle microwave glow in all directions, a snap shot in time of the moment when matter as we now understand it formed, an era we call recombination.
We also bathe in the visible light from our own star and on Wednesday morning that light will be momentarily blocked as the moon and the sun interact in the dance of orbital mechanics and create a shadow that will sweep across a vast tract of the Earth’s surface.
A lucky few will witness a beautiful cosmic coincidence, the moon covering the Sun. A coincidence that perhaps is unique across the cosmos and one that will only exist for a brief moment as the march of stellar and planetary evolution eventually conspire to make the Sun bigger and the move the moon further away.
Happy Diwali everyone!