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Reflection: Why is it Dark at Night?

by Emily Peavy on March 9th, 2017

‘Imiloa invited Dr. Tom Geballe, Astronomer at Gemini Observatory, to the planetarium where he discussed the phenomenon of the dark night sky in Why is it Dark at Night? A Modern Look at Olbers’ Paradox.


Darkness Between the Stars

The first astronomical observation that every child makes is that the sky is dark at night. While we do see the pinpoint light of stars peeking through the void, as a whole the sky is dark. As we grow older, we learn that the stars that make up the nighttime sky are but a small fraction of the billions of stars that stretch across the universe. However, if there are so many stars across the whole universe, why isn’t our night sky shining bright with their combined brilliance?

Old Ideas of Cosmology

Before the advancement of Einsteinian physics and Hubble’s observations of the expanding universe—astronomers and philosophers had the natural assumption that the universe was static. A static universe means neither contracting nor expanding, with no beginning, a universe that has always existed, with an infinite number of stars shining perpetually. With this theory, no matter how far away a star is from Earth, its light would have time to reach Earth and every line of sight would end with a star.

However, today we have a different model of the universe. We know that the universe does not contain an infinite number of stars, just about 10 billion trillion stars. We also know that the universe is expanding out in all directions, and has been since its creation from the Big Bang 13.7 billion years ago. The nighttime sky is dark due to the universe’s immense present size and these properties.


Don’t miss our next Astronomy Talk, The NEO Hazard: NASA and Planetary Defense on Saturday, March 11 at 7:00 p.m. in ‘Imiloa’s planetarium. Rob Landis and Dr. Kelly Fast of NASA will discuss possible asteroid impacts on Earth and NASA’s protection efforts with the newly established office: the Planetary Defense Coordination Office.

We also have an exciting presentation coming up titled Learning to Live on Mars… on Mauna Loa, which is part of our Maunakea Skies series on Friday, March 17 at 7:00 p.m. Brian Shiro, Geology Lead at the Hawai’i Space Exploration Analog Simulation (HI-SEAS), will discuss their program that researches how crews will function on long-duration missions to Mars.
For more information on events at ‘Imiloa, visit our Event Calendar. Tickets are $10, $8 for members. Pre-purchase your tickets at ‘Imiloa’s front desk or over the phone by calling 808-932-8901.


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