On June 6, 2012 (April 17 of the lunar calendar year 2012), the last "transit of Venus" celestial phenomenon in the 21st century. Picture: The "transit of Venus" celestial phenomenon will take 105 years to miss. "Black droplets" and "halos" will be visible in the sky on June 6. A rare astronomical phenomenon - the transit of Venus will be staged in the sky. Zhao Junliang, former director of the Shanghai Astronomical Observatory and honorary director of the Shanghai Astronomical Society, introduced at a lecture organized by the Shanghai Astronomical Observatory that if this observation opportunity is missed, the next transit of Venus will not be until 2117. He also revealed that the principle of the transit of Venus can be used to find aliens. Observing the transit of the sun can see "black drops" and "halos." On the morning of June 6, if the weather is clear, citizens in the central and eastern regions of our country can see a small black dot moving slowly on the surface of the sun, which is the transit of Venus. According to Zhao Junliang, the characteristic moment of the transit of the sun in Shanghai is: 6:10:57 Ling begins to cut (Venus just begins to contact the sun); 6:28:46 Ling begins to cut (Venus completely enters the sun); 12:30:58 Ling ends to cut (the edge of Venus leaves the sun); 12:48:30 Ling ends to cut (Venus completely leaves the sun), and the whole process will last for more than 6 hours. Due to the fact that Venus orbits the sun faster than the earth, the transit path is moving from the left to the right of the sun. The principle of a transit of Venus is actually similar to that of a solar eclipse. The earth, Venus and the sun are in a straight line, and the small black spot image of Venus appears on the sun's circle. The transit of Venus is relatively rare. There has been no transit of Venus in the entire 20th century. The most recent one was on June 8, 2004, but the citizens of Shanghai only saw it halfway at that time. When the sun went down, the transit of Venus had not ended. Fortunately, the citizens could watch the whole journey on June 6 this year. Zhao Junliang suggested that during the transit of Venus, citizens should strive to observe two interesting phenomena, "black droplets" and "halos", both of which appear in the short time after the transit and before the transit. The "black droplet" effect shows that during the transit, when Venus and the sun are inwardly cut, the edge of Venus and the edge of the sun are "glued" by oil droplet-like black shadows, which is related to atmospheric tranquility, light diffraction and limited telescope resolution. During the transit and transit stages, sometimes the edge of the Venus circle will be inlaid with a very thin "halo" or "halo", which is formed by the reflection and scattering of sunlight from the top of the Venus atmosphere. In 2012, the "transit of Venus" celestial phenomenon Venus transit principle can be used to find aliens Venus transit is not only a rare astronomical phenomenon, but also can be used to detect planets outside the solar system. According to Zhao Junliang, in order to find aliens, humans have sent strong radio signals to space, and have also sent spacecraft carrying "Earthman business cards" and "Voice of the Earth" records, but so far there has been no reply from aliens. Since the 1980s, astronomers have begun to use the planet transit method to detect possible planets around other stars outside the solar system. Astronomers imagine that if there is one or more alien planets orbiting around the star, then it is possible to observe that the planet will periodically pass in front of the star, which is a planet transit. During a planetary transit, the star's brightness will decrease as a result, and it will show a very regular periodicity, which can detect the existence of planets around the star. Finding a suitable planet will be the first step in finding aliens. In 2009, the United States launched the Kepler Space Telescope, which is dedicated to searching for alien planets through the planet transit method. Its high-precision photometry can ensure the detection of alien planets the size of Earth and even smaller. Between May and September 2009, "Kepler" discovered 1,235 candidate planets around 997 stars, which is more than twice the number of alien planets found before. Astronomers are still using this method to find more planets. [ Practical Reminder] It is rare to see the transit of Venus with a solar eclipse observation card. To observe successfully, you must be fully prepared. Tang Haiming, director of popular science at the Sheshan Station of the Shanghai Observatory, reminded the public that the most important thing is to pay attention to protecting your eyes, and you must not observe directly with the naked eye or wearing ordinary sunglasses. In order to fully weaken the sun's rays, citizens can use the solar eclipse observation card. Some citizens also have the solar eclipse observation card purchased during the 2009 total solar eclipse. Before using it, you need to check whether it is damaged. In addition, it is also a good choice to observe with a telescope, but the telescope needs to be equipped with filters first. In addition, citizens can also watch the live broadcast of the transit of Venus at the Shanghai Observatory through the Internet.