On this day, 56 years ago, on January 5, 1969 (November 17, 1968 in the lunar calendar), the former Soviet Union launched an unmanned spacecraft to Venus. On January 5, 1969, the former Soviet Union launched the Venus-5 Venus probe. Five days later, the "Venus-6" probe was launched. On May 16, 1969, the descending enclosure of the Venus-5 probe entered the atmosphere of Venus on the back side of Venus and began to send back atmospheric detection data from Venus. The picture shows the "Venus 5" probe stamp issued by the former Soviet Union in 1969. Except for the sun and moon, Venus is the brightest star visible to the naked eye in the sky. Venus is adjacent to the Earth. When it is closest, it is 41 million kilometers. Its diameter is about 4% smaller than the Earth, its mass is 20% lighter, and its density is 10% lower. Because it resembles the Earth in terms of size, density, quality, and appearance, it is known as the Earth's "twin sister". In fact, Venus is very different from Earth in many ways. For example, its rotation is reversed, that is, from east to west, with a period of about 243 days, which is 18.3 days longer than its orbit around the sun of 225 days. Venus is about 1/3 closer to the sun than the earth, and it receives twice as much solar light as the earth. Human space exploration of planets in the solar system first began with Venus. Since the 1960s, the Soviet Union and the United States have been extremely enthusiastic about unveiling the secrets of Venus. The former Soviet Union launched the "Giant" Venus probe on January 24, 1961, and crashed due to a launch vehicle failure during launch in space. On February 12, 1961, the test launch of "Venus 1" was carried out. This probe that successfully flew to Venus weighed 643 kilograms and flew 96,000 kilometers away from Venus. After entering orbit around the sun, it lost contact. As a result, it found nothing. Later, the Venus 2-4 probe was launched. On January 5, 1969, the Soviet Union launched the "Venus 5" probe and finally landed on the surface of Venus. During the descent of the landing module, 53 minutes of detection data were obtained. When the landing module fell to about 24 to 26 kilometers from the surface of Venus, it was damaged by atmospheric pressure, and the pressure at this time was 26.1 atmospheres. "Venus 5" is the first victory in human exploration of Venus.