How do we define the time interval of one "second" now, and keep track of elapsed time accurately enough to navigate spacecraft through the solar system, or place you on Earth with a GPS receiver? From the daily rotation of Earth with respect to distant stars. Counting cycles of oscillation in a cesium atom, the so-called "atomic" clock. From the daily rotation of the Earth on its axis. From the annual revolution of Earth about the Sun starting at noon on one year and ending at noon on the following year.
Stellar evolution
We may see thousands of stars in the dark sky. Our universe consists of billions of stars. Stars may appear tiny to us but they are huge balls of gasses. Sun is a star of average size. Some stars are even a thousand times larger than the sun. The stars do not exist forever they have a certain lifetime. The life span of the sun is about 10 billion years. The star undergoes various changes during its lifetime, this process is called stellar evolution. The structure of the sun-like star is shown below.
Red Shift
It is an astronomical phenomenon. In this phenomenon, increase in wavelength with corresponding decrease in photon energy and frequency of radiation of light. It is the displacement of spectrum of any kind of astronomical object to the longer wavelengths (red) side.
How do we define the time interval of one "second" now, and keep track of elapsed time accurately enough to navigate spacecraft through the solar system, or place you on Earth with a GPS receiver?
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From the daily rotation of Earth with respect to distant stars. |
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Counting cycles of oscillation in a cesium atom, the so-called "atomic" clock. |
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From the daily rotation of the Earth on its axis. |
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From the annual revolution of Earth about the Sun starting at noon on one year and ending at noon on the following year. |
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