 |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
 |
 |
 |
 |
 |
 |
 |
 |
|
||||||||||||
 |
 |
 |
|
|||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
|
||||||||||||||||||||
 |
 |
 |
 |
 |
|
|||||||||||||||
 |
||||||||||
| Transits of Venus have long been useful to scientific research. In the 1700s, they helped us determine our distance to the Sun and gave us the first clue that Venus might have an atmosphere. | ||||||||||
| How do we know how far away the Sun is? Now we use radar to establish our distance from celestial objects, but before there was radar, we had to resort to trigonometry to figure out the astronomical unit (AU)—the distance between Earth and the Sun. In 1677, English astronomer Edmond Halley (of comet fame) proposed that a transit of Venus—and some geometry—could be used to determine the astronomical unit. Though Halley died in 1742, which was 19 years before the 1761 transit of Venus, other scientists followed his suggestion and journeyed to the ends of the Earth to make the necessary observations. The astronomical unit obtained from these observations, roughly 95 million miles, is respectably close to our current measure of 92,955,807.267 miles (149,597,870.691 kilometers). | ||||||||||
| It was also during the 1761 transit of Venus that observers noticed something strange: a fuzzy halo of light surrounding the dark spot of Venus. 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 .01 percent for a planet the size of Earth.) 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. | ||||||||||
| In 2007, NASA will launch the Kepler Mission, which will use a space telescope to search for Earth-sized exoplanets. Kepler will watch 100,000 stars that are similar to our Sun, looking for variations in brightness caused by planets transiting their parent stars. (For more information, go to http://www.kepler.arc.nasa.gov.) | ||||||||||
|
||||||||||
|
 |
 |
|
