Observations from different locations on Earth allowed scientists to not only triangulate the true size of the sun but also to more accurately determine the distance between the sun and Earth. Based on the 18th-century transit, astronomers calculated that the sun is 95 million miles million kilometers away—only slightly off from the true Earth-sun distance of 93 million miles million kilometers. Today, 21st-century astronomers hope to use the transit of Venus to collect data on the planet's atmosphere and compare their findings to measurements from the European Space Agency's Venus Express orbiter.
The orbiter has returned information on intriguing weather patterns in Venus's dense atmosphere, but at close range the craft can see only one region at a time.
The transit, meanwhile, will allow astronomers to get a broader picture of Venuvian weather in the planet's upper atmosphere and see how different regions interact. In addition, scientists using the NASA-ESA Hubble Space Telescope will use the transit to help improve techniques for finding and characterizing planets around other stars, aka exoplanets. With its sensitive instrumentation designed to peer deep into the cosmos, Hubble can't look directly at the sun.
Instead astronomers will have the orbiting observatory aimed at the moon to watch for the slight drop in reflected sunlight during the transit. The hope is that Hubble's activity will be a good parallel to observations currently being carried out by NASA's Kepler spacecraft , which looks for dips in starlight caused by planets transiting their host stars, as seen from Earth. A prolific planet hunter, Kepler has already racked up 61 confirmed planets and more than 2, planetary candidates.
However, "since the stars are so far away that no details can be seen, those exoplanet transits are visible only in the total light of the star," Williams's Pasachoff said. Scientists therefore have to make a number of estimates when analyzing Kepler data to tease out a planet's size and atmospheric properties. Watching how the sun's light changes during the Venus transit can show astronomers whether their calculations capture the known properties of a nearby planet, helping them to refine their models for studying more distant worlds.
All rights reserved. Early this week sky-watchers around the world will be able to witness a transit of Venus —a celestial event that won't be seen again for more than a century.
Visible either Tuesday or Wednesday, depending on where you live, the transit will offer astronomers a chance to refine our understanding of Venus as well as to tweak models for searching for planets around other stars. Pictures: See what the Venus transit will look like. Share Tweet Email. That's why they don't meet up on exactly the same alignment very often. Another eight years on, it will be a little more ahead again, and that will continue for another and-a-half years — until it eventually catches Earth again, at the other side of the Sun.
After that, Venus will inch ahead again, and won't catch Earth again for another and-a-half years. By the time it takes Earth to go around the Sun times, Venus has gone around times and they almost exactly line up again give or take about nine hours or so. He was interviewed by Stuart Gary.
Tags: astronomy-space , planets-and-asteroids. Email ABC Science. For the descending-node transits separated by 8 years, Venus crosses the southern part of the Sun's disk in the first transit, and the northern part the second time around. When Venus came to inferior conjunction in , it was too far below the Sun to transit its disk. And in , it will be too high. The opposite is the case for ascending-node transits. The first transit in an 8-year pair crosses the northern part of the Sun, the second one crosses the southern half.
This asymmetry is due to the fact that Earth's orbit around the Sun is not quite a perfect circle. It's slightly elongated the technical term is eccentric , deviating from a perfect circle by about 3 percent. In contrast, Venus's orbit is so close to being a perfect circle that its minuscule elongation can be ignored in this discussion. The Earth's elongated eccentric orbit exaggerated in the diagram explains why there is an asymmetry in the amount of time from one transit pair to the next.
Basically, Earth is near its farthest point from the Sun aphelion in June and near its closest point to the Sun perihelion in December. When Earth is closer to the Sun's powerful gravity, it moves slightly faster in its orbit than when it's farther from the Sun.
In the future, transits of Venus will become even more rare. This diagram shows the track Venus will take across the Sun in In and , Venus's path will miss the Sun from Earth's perspective. Both Venus's and Earth's orbits precess, meaning they rotate over long time periods to produce a rosette-like pattern.
In other words, Earth's perihelion shifts in its orbit, and so does Venus's. Because of precession, Earth-bound astronomers will only be able to enjoy one ascending-node transit for centuries after the year They will see a descending-node transit in , but 8 years later, in , Venus will come to inferior conjunction too far above the Sun to transit its disk.
It happens from time to time that Venus comes between Earth and the Sun, an event called an inferior conjunction. A Venus transit is similar to a solar eclipse, in which the face of the Sun is blocked by the Moon.
The orbit of Venus around the Sun is tipped in relation to the orbit of Earth. As viewed from the Sun, the orbits cross at two points called the nodes , and it is only at these points that the planets and the Sun line up directly Fig.
This animation shows Venus from the perspective of the moving Earth. Here you see the position of Venus relative to Earth's orbit the green line in the few months leading up to June 8, , and then watch as Venus transits the Sun on that date.
0コメント