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Web icon An illustration of a computer application window Wayback Machine Texts icon An illustration of an open book. Books Video icon An illustration of two cells of a film strip. Video Audio icon An illustration of an audio speaker. Audio Software icon An illustration of a 3.
Software Images icon An illustration of two photographs. Images Donate icon An illustration of a heart shape Donate Ellipses icon An illustration of text ellipses. Encyclopedia Of Knowledge Item Preview. The most distant objects visible are galaxies photographed by the Hubble Telescope.
We see them as they were 13 billion years ago. The elements hydrogen and helium make up 98 percent of the matter we can see in the Universe. As a result, astronomers think galaxies contain dark matter, which we cannot see. There is also an unknown force making the Universe expand, known as dark energy. In this series of pictures, each stage represents a microscopic speck of the image to its right.
Instead, astronomers use the speed of light as a yardstick. Light is so fast it can travel around the Earth 7. One light year is the distance light travels in a year: nearly 6 trillion miles 10 trillion km. Do you like this book? Please share with your friends, let's read it!! Search Ebook here:. Book Preface The Universe is the whole of existence—all of space, matter, energy, and time. Designed by readallbooks. Download here Download Now here.
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