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With the advent of spacecraft and radar, more precise methods emerged for making a direct measure of the distance between the Earth and the sun.
The definition of AU had been "the radius of an unperturbed circular Newtonian orbit about the sun of a particle having infinitesimal mass, moving with a mean motion of 0. Along with making things unnecessarily difficult for astronomy professors, that definition actually didn't jibe with general relativity. Using the old definition, the value of AU would change depending on an observer's location in the solar system.
If an observer on Jupiter used the old definition to calculate the distance between the Earth and the sun, the measurement would vary from one made on Earth by about 1, meters 3, feet.
Moreover, the Gaussian constant depends on the mass of the sun , and because the sun loses mass as it radiates energy, the value of AU was changing along with it.
The International Astronomical Union voted in August to change the definition of the astronomical unit to a plain old number: ,,, meters. The measurement is based on the speed of light, a fixed distance that has nothing to do with the sun's mass. Both Klioner and Capitaine were both part of the International Astronomical Union group that worked to refine the definition.
The sun is at the heart of the solar system. All of the bodies in the solar system — planets, asteroids, comets, etc. Mercury, the planet closest to the sun, gets as close as 29 million miles 47 million km in its elliptical orbit, while objects in the Oort Cloud, the solar system's icy shell, are thought to lie as far as 9. Everything else falls in between. Jupiter , for example, is 5. The fuzzy halo was only visible when Venus was at the Sun's edge.
Scientists of the time concluded that Venus must have an atmosphere, and we've since confirmed that it does: a dense atmosphere of mainly carbon dioxide, with clouds of sulfuric acid.
Transits are still of interest to scientists today, because they can be used to find planets outside our solar system, also known as extrasolar planets, or exoplanets.
Extrasolar planets are too distant and too dim to be viewed directly, but when one passes in front of that is, transits its parent star, it blocks a little bit of the star's light.
The dimming is detectable but extremely slight; just 1 percent for a giant planet like Jupiter and. Scientists analyzing the changing light from stars can not only identify the presence of a planet, but can also determine the planet's size, temperature, and atmospheric composition.
The transit of Venus provides great practice for these scientists, allowing them to track the optical changes that take place during a transit. Kepler watches more than , stars that are similar to our Sun, looking for variations in brightness caused by planets transiting their parent stars. For more information, go to www.
By , German astronomer Johannes Kepler had figured out the relative distances of all the planets from the Sun. For example, if the Earth's distance from the Sun is one astronomical unit AU , then Venus's distance from the Sun is.
However, no one knew the value of AU, so the absolute distances between the celestial spheres were not known. In , English astronomer Edmond Halley proposed a method for calculating our distance from the Sun—the astronomical unit—using the transit of Venus.
The underlying principle behind Halley's method is something called parallax, the shift in position that comes from viewing an object from two different points.
What is parallax? Try this. Try this: Point your index finger towards an object on the opposite side of the room.
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