Science Time Machine | How was Uranus discovered?

Uranus is the first planet in human history to be observed with the help of a telescope. This discovery is attributed to the outstanding British astronomer Friedrich William Herschel, who is known as the "founder of stellar astronomy." On March 13, 1781, Herschel accidentally captured the image of Uranus, a mysterious celestial body, while conducting astronomical exploration with a telescope in his courtyard.

That night, Herschel was attracted by an unprecedented bright spot in the sky, and he initially speculated that it might be a newly discovered comet. However, with the in-depth observation and accumulation of data, Herschel keenly noticed that the trajectory of the light spot was very different from the known comet orbit. After rigorous analysis and comparison, Herschel finally concluded that this unique light spot was not a comet, but a brand new planet in the solar system. The planet was named Uranus.

From geocentrism to heliocentrism

Since ancient times, human beings have never stopped exploring the universe. Take the exploration of the solar system as an example. As early as in ancient times, humans have recognized the existence of major planets such as Mercury, Venus, Mars, Jupiter and Saturn. The geocentric theory of ancient Greek astronomer Ptolemy proposed that the sun and these five planets revolve around the earth. In the 15th century, astronomer Copernicus proposed the heliocentric theory, pointing out that Mercury, Venus, Earth, Mars, Jupiter and Saturn revolve around the sun.

From the time when the heliocentric theory was proposed to the Industrial Revolution in the 18th century, the astronomical community gradually reached a consensus that the solar system only contains six planets: Mercury, Venus, Earth, Mars, Jupiter and Saturn. However, astronomers have not stopped exploring other planets in the solar system.

Before Herschel, some scientists had observed Uranus but mistook it for a star. Although these scientists' cognition was different from the actual situation, their discovery laid the foundation for Herschel's subsequent exploration of Uranus. In 1690, astronomer Flamsteed observed Uranus through a telescope, but due to the limitations of observation methods, he mistook it for a star in Taurus. Between 1750 and 1759, French astronomers observed Uranus at least 12 times. Although they did not confirm it as the seventh planet in the solar system, they provided Herschel with valuable observation clues and reference materials.

The first planet discovered with a telescope

Friedrich Wilhelm Herschel was born in Germany in 1738 and moved to England in 1758. Born into a musical family, fate paved a brighter path for him in astronomy. His father was not only proficient in the mysteries of music, but also an astronomy fan with an infinite love for the starry sky. Under the influence of his father, Herschel developed a strong interest in astronomy from an early age. The constellations in the night sky were as familiar to him as old friends.

While studying music theory, Herschel came across a scientific work, Opticks. This classic not only elaborated on the principles of making telescopes and microscopes, but also had a chapter dedicated to discussing "the discovery of stars by telescopes." These contents were like a key that opened the door for Herschel to explore the mysteries of the universe and inspired his strong desire to observe and study celestial bodies.

Since ancient times, human beings have never stopped their curiosity and exploration of the universe, and Herschel is no exception. In 1773, he read the book "Astronomical Explanation of Sir Isaac Newton's Principia", and the distant and mysterious celestial bodies described in the book made him yearn for it. In order to see the celestial bodies described in the book with his own eyes, he began his own astronomical observations. At first, he used a refracting telescope, but the effect was not ideal. In order to find a more suitable tool for exploring the universe, he decided to try a reflecting telescope.

From 1774 to 1787, Herschel kept trying to make telescopes by himself. He gradually mastered the technology of grinding parabolic reflectors and successfully installed several reflecting telescopes. In order to improve the efficiency of light gathering and reduce the loss of refracted light, he designed a unique optical system, known as the "Herschel Telescope". With this self-created tool, he successfully observed the Orion Nebula for the first time and clearly identified the rings of Saturn. From then on, he not only conducted sky surveys tirelessly at night, but also often focused on grinding telescope mirrors during the day.

On the night of March 13, 1781, Herschel, as usual, held a 15cm-diameter reflecting telescope and looked up at the vast starry sky. When his eyes turned to Gemini, a strange and bright star attracted his attention. He looked through all the star maps, but could not find any trace of this star. So he changed to a higher-power eyepiece, more than 400 times, more than 900 times... After careful observation, he was sure that this was not an ordinary star. Because no matter how the magnification of the telescope increased, the blue-green outline of the star remained as clear as before. To be cautious, astronomer Herschel did not rush to announce the discovery, but kept a close eye on the mysterious little planet for ten consecutive nights. Gradually, he noticed that the planet was moving slowly every day at an almost imperceptible speed.

After a period of patient observation, Herschel used the collected data to carefully calculate the orbit of the planet and found that it was almost a perfect circle and twice as far away from the sun as Saturn. At this time, he realized that he might have discovered a brand new planet. As more observation data accumulated, the astronomical community finally confirmed this amazing discovery: there is indeed a new planet in the solar system, and its distance from the sun is twice as far away as Saturn, the farthest known planet at the time.

The news of Herschel's discovery of a new planet quickly caused a sensation. In order to commemorate this great discovery, the new planet was named "Uranus", which comes from the name of Saturn's father in Greek mythology.

The formation and evolution of Uranus

The history of Uranus' formation can be traced back to the early days of the solar system, about 4.6 billion years ago. At that time, a huge cloud of gas and dust began to collapse under the influence of gravity, eventually forming the original sun. As this process progressed, the remaining matter revolved around the sun and gradually accumulated, and some of the matter may have condensed into Uranus.

During the formation of Uranus, extreme temperatures and pressures triggered complex chemical reactions inside the planet, producing high-density gases, mainly hydrogen, helium and methane, which constitute its atmosphere. The unique blue color of Uranus' atmosphere is attributed to the specific absorption and scattering effect of methane gas on sunlight.

Uranus has a complex internal structure and is speculated to have a rocky core surrounded by a thick layer of ice that may contain compounds such as water, ammonia and methane. In addition, Uranus has a very special magnetic field, with the magnetic pole tilted at an angle of more than 90 degrees to the rotation axis, presenting a nearly "lying" state.

Uranus has experienced many major events in its long evolution. It may have been hit by large celestial bodies, which had a profound impact on its rotation axis tilt and magnetic field shape. At the same time, Uranus' atmosphere has also undergone significant changes, forming a complex cloud system and storm system, the most notable of which is a huge storm with a diameter of 25,000 kilometers that has existed for decades - the "Great Blue Spot".

Reference sources: China.com, Science China, CCTV.com