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We are always searching for clocks of greater precision which means that during each cycle of the clock there is little deviation from period to period.
We have a periodic motion of the earth with its diurnal rotation on its axis.
Astronomers focusing on a star at the center of the Milky Way say they have measured precisely for the first time how long it takes the sun to circle its home galaxy: 226 million years.
The last time the sun was at this exact spot of its galactic orbit, dinosaurs ruled the world.
The earth orbiting the sun is one periodic motion that repeats itself that we use to measure time.
The rotation of the earth on its axis is another motion we use to measure time.
He also showed that stars farther from the center have a combined gravitational force of zero.
Those stars pull in all different and opposite directions, canceling out one another.
For their solar system measurement, the astronomers focused on Sagittarius A, a star discovered two decades ago to mark the Milky Way's center.Sometimes these motions depart from exact repetition even if just by a second.We can call any instrument used to measure time a clock.A report on the finding was presented Tuesday at a national meeting of the American Astronomical Society."Our new figure of 226 million miles is accurate to within 6 percent," Mark Reid, a Harvard-Smithsonian astronomer and leader of the team that made the measurements, said in a statement. Working together as a single unit, the antennae can measure motions in the distant universe with unprecedented accuracy.
Using a radio telescope system that measures celestial distances 500 times more accurately than the Hubble Space Telescope, astronomers plotted the motion of the Milky Way and found that the sun and its family of planets were orbiting the galaxy at about 135 miles per second.