How did the ancients see Mars?

Author: Fan Yu (Lunar and Deep Space Exploration Department of the Chinese Academy of Sciences, National Space Science Center of the Chinese Academy of Sciences)

The article comes from the Science Academy official account (ID: kexuedayuan)

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Humans have never stopped exploring the unknown. Even in the face of the vast universe, humans are just a drop in the ocean, but they have never stopped. Today, people can use various space probes to conduct all-round exploration of Mars. So, in the era when there were no spacecraft, how did people observe it? What stories happened during the process of our predecessors' exploration of Mars?

Ancient China: Does Mars mean bad luck?

The oldest way of observation is to look directly with your eyes. Astronomy is one of the most developed natural sciences in ancient China. People have made detailed observations and records of the sun, moon, planets, comets, meteor showers, etc. In ancient China, humans in primitive society had already begun to try to "observe the sky." In the 24th century BC, during the reign of Emperor Yao, officials such as Huo Zheng and Xihe were set up to observe the sun, moon, and stars, specializing in "observing phenomena and setting time."

Suzhou Stone Astronomical Map (Source: Chinese Ancient Astronomical Atlas)

In ancient times, people believed that celestial phenomena were omens from heaven, and astronomical observations related to Mars were always associated with disasters and ominous signs. Today, we all know that due to its orbit, the closest distance between Mars and the Earth is about 55 million kilometers, and the farthest distance is more than 400 million kilometers. In the observations of the ancients, Mars was red and had a fiery fluorescence, representing fire in the five elements. The brightness of Mars is not fixed, sometimes bright and sometimes dark, and it moves back and forth between the east and west in the sky. The pattern is unpredictable and very confusing. Therefore, the ancients also called Mars "Yinghuo", which was taken from "fluorescent firelight, confusion and confusion". There are many records of Mars astronomical phenomena in ancient China, and "Yinghuo guarding the heart" is one of the most influential ones.

The "heart" refers to Antares in Scorpio, a super-large red giant in the Milky Way. It was called "Big Fire" in ancient times. It is the brightest star in Scorpio. It is blood red and even one of the brightest stars in the entire night sky. When Mars moves to Antares and lingers for more than 20 days, it will form "Mars in the Heart".

According to historical records, in the year when "Mars in the Heart" occurs, the country will encounter major disasters, either natural disasters or man-made disasters. Therefore, this is the astronomical phenomenon that every emperor least wants to see when ruling a country. However, in fact, based on the current astronomical concepts, most of the "Mars in the Heart" astronomical phenomena recorded in history have errors or are even fabricated, and their ominous predictions are mainly used as a means of political struggle. However, this also further illustrates that in ancient China, due to the variability and uncertainty of Mars, it became a symbol of ominousness.

From naked eye observation to the advent of telescopes

In Western society, Mars also represents war. The ancient Egyptians before Christ called it the "Red Star"; the ancient Babylonians called it the "Death Star"; the ancient Greeks named Mars after the god of war "Ares" in the "Homer's Epic", and the later ancient Romans also named the planet after their own god of war "Mars". From then on, Mars in the Western world had an official name: Mars.

Ares, the god of war in Greek mythology (Image source: Baidu Encyclopedia)

Although Western society knew about the red planet as early as BC, it was not until the Renaissance (14th-16th centuries) that Mars gained further knowledge. Danish astronomer Tycho Brahe spent more than 20 years observing many astronomical phenomena with his eyes and recording relevant data, including a large amount of observation data on Mars. His disciple Johannes Kepler, while studying and analyzing the data left by Tycho, was also observing Mars in the universe. He found that Mars orbits the sun along an elliptical orbit, with the sun at one of the two foci. Then he found that the speed of Mars is uneven. When it is closer to the sun, it moves faster (perihelion), and when it is farther away from the sun, it moves slower (aphelion), but starting from any point, the radius (the line connecting the center of the sun to the center of the planet) sweeps the same area in equal time.

These are the famous Kepler's orbital law and area law. Later, in 1619, he published his third law. This is the foundation of modern astronomy, Kepler's three laws: all planets move in elliptical orbits of different sizes; in the same period of time, the area swept by the planet's radius on the orbital plane is equal; the square of the planet's revolution period is proportional to the cube of its distance from the sun.

Kepler's contribution is not limited to this. In 1609, Galileo used the Dutch telescope to create the first astronomical telescope in human history, the Galileo telescope. In 1611, Kepler modified the telescope based on Galileo's, making the field of view larger. It was called the Keplerian telescope. The emergence of ground-based optical telescopes enabled humans to observe Mars and other planets more clearly. From then on, human astronomical observations reached a new level, from naked eye observations to the era of astronomical telescope observations.

Over the next 200 years, humans have further observed Mars through telescopes and have a clearer understanding of it. In 1659, Dutch scientist Huygens used an advanced telescope designed by himself to record a large black spot on Mars. He noticed that the black spot returned to its original position at the same time the next day, so he calculated that Mars has a 24-hour cycle; in 1666, French astronomer Cassini observed Mars and determined that its rotation period, or Martian day, is 24 hours and 40 minutes; in 1672, Huygens first observed a white spot at the South Pole of Mars, which may be the polar cap.

Martian satellites and the discovery of the "canals"

In 1877, Asaph Hall, working at the United States Naval Observatory, discovered two satellites of Mars during a close approach of Mars, which he later named Phobos and Deimos. In the same year, Italian astronomer Giovanni Virginio Schiaparelli claimed to have discovered "cannali" on Mars, an Italian word that was mistranslated into English as "canals" but originally meant "river channels". He drew a map of the surface of Mars that later became one of the standards for planetary mapping and was used until the advent of the space age.

Lowell's hand-drawn map of Mars (Image source: National Geographic Maps)

In 1894, American Percival Lawrence Lowell funded the construction of the Lowell Observatory in the United States. He was obsessed with astronomical observations and spent 15 years taking a large number of photos of Mars and drawing a map of the "canals" on Mars. He was also the most influential popular science writer of that era and published many novels about Mars. However, the theory about the "canals" on Mars was also controversial at the time.

In 1909, Greek astronomer Eugene Antoniadi used the 83cm telescope of the Paris Observatory to observe and announced that the so-called canals on Mars might just be an optical illusion. There is an Antoniadi impact crater on Mars and the Moon to commemorate it, and there is also a cliff on Mercury named "Antoniadi Dorsum". In 1950, scientists at the Lowell Mars Observatory proposed that the so-called canals on Mars might be cracks on the surface of Mars, and pointed out that the oases with radial structures on the surface are actually impact craters, and the so-called canals are cracks formed by the impact.

A topographic map of Mars created using data from the Mars Global Surveyor (Image credit: NASA)

In the 1960s, humans were no longer satisfied with observing Mars from Earth and began to try to launch Mars probes, thus opening the chapter of space exploration.

Over the past 3,000 years, human curiosity and the desire to understand the unknown have allowed us to gradually understand the universe. Because of ignorance and fear, various myths have emerged; in an attempt to understand, people use their naked eyes to survey the celestial phenomena, hoping to get inspiration from heaven; after exploring certain laws, humans created telescopes to explore and observe the distant Mars; now, humans can approach and land on Mars through probes to directly understand and study the characteristics of this planet.

Science and technology are developing so rapidly that perhaps in the near future, humans will really be able to travel to the more distant universe and explore more unknown mysteries.