The story of the ancient Greek astronomer Hipparchus

  In August 1989, the European Space Agency launched an astrometric satellite called “Hipparco” with the Ariane carrier rocket. This satellite has been working diligently for 4 years and has achieved fruitful detection. It measured a total of nearly 120,000 stars as dim as 12th magnitude, and determined their right ascension and declination with an accuracy error of less than two thousandths of an arcsecond. The Hipparcos satellite also determined the speed and direction of the stars, as well as their respective magnitudes. These valuable observational data were immediately used for the establishment of the celestial reference system, the correction of stellar distance scales, the structure and evolution of stars, and the modern theory of the universe.
  Why was this satellite named “Hipparco”? That’s a long story. Two thousand years ago in ancient Greece, there was an accomplished astronomer and mathematician Hipparchus, known as the “father of astronomy”. He served as the director of the famous Alexandria Library, and later in the Mediterranean Sea Rhodes conducted long-term star observation activities. He founded “azimuth astronomy”, and for the first time proposed a method to distinguish the brightness of stars by the concept of “magnitude”, and also discovered the astronomical phenomenon of “precession”. He compiled his life’s observations into a catalog that calibrated the positions and brightness of more than 1,000 stars, laying the foundation for many subsequent astronomical discoveries. In honor of the famous astronomer Hipparchus, the astrometric satellite was named “Hipparcos”. (“Hipparcus” is another translation of “Hipparchus”.)
  Hipparchus’ successor was the famous Ptolemy, who completed the theory of “geocentric theory” and wrote “The Great Work of Astronomy” ” was later regarded as a classic and has been handed down to this day. And what connects them is the famous Library of Alexandria. The Library of Alexandria was founded in 259 BC and was once known as the “beacon” of the human civilization world. Together with the Lighthouse of Alexandria, it became a symbol of the city of Alexandria. It houses many philosophical, poetic, literary, medical, religious, ethical and scientific works, and at its peak, it collected more than 500,000 volumes of various manuscripts.
  Eratosthenes, who is regarded as the “father of geography” by Western geographers, and Aristarchus, the ancient Greek astronomer who was the first to advocate geocentric theory, have all served as the curator of the Library of Alexandria. Pachas also served as the director of this library, and also deposited all his works in this library with the highest specifications at the time.
  In AD 127, the young Ptolemy was sent to the culturally rich city of Alexandria to study. In the Library of Alexandria, he read a wide range of books, read all the works of Hipparchus, admired him immensely, and got inspiration from it, and completed the masterpiece “Astronomy”.

  Unfortunately, in 642 AD, the Arab general Amur occupied the city of Alexandria. He not only burned down the library, but also handed over all the books in the library to the more than 4,000 public baths in the city for fuel, burning 6 of them. month long. Hundreds of thousands of books were burned in this way, including Hipparchus. So to this day, we know very little about Hipparchus’ life, and what we know about his accomplishments comes entirely from the writings of Ptolemy, which were circulated around the world.
  With limited information, later generations summed up the nine achievements of Hipparchus in astronomy:
  1. After many years of stargazing on Rhode Island, he created his own astronomical observatory, and invented a system that can observe the positions of the stars with the naked eye. Instrument, this instrument has been used in the West for more than 1700 years. In order to identify the “novae”, he decided to compile a star table, indicating the exact position of the stars on the celestial sphere, so that the “guests” in the starry sky can be found in time.
  2. Determination of “magnitude”. In order to clearly reflect the brightness of stars, Hipparchus classifies the brightness and darkness of stars into grades. He regarded the 20 brightest-looking stars as first-magnitude stars and the faintest stars seen by the eye as sixth-magnitude stars. It is further divided into second, third, fourth and fifth star. This classification according to the relative brightness of the stars is called “magnitude”. The concept of “magnitude” proposed by Hipparchus more than 2,100 years ago is still in use today.
  3. Discover “precession”. Hipparchus compared his observations of stars with those of Aristyr and Timothyris 150 years ago, and found that the stars in the sky move uniformly from west to east. He explained as follows: Suppose The north pole of the celestial sphere makes a slow circular motion in the air, and it takes 26,700 years to complete one week. He calculated that the sky moved westward by 1° every 100 years, moving 36″ per year (the current measurement is 50″). This means that the vernal equinox, summer solstice, autumn equinox, and winter solstice are slightly earlier each year, a phenomenon called “precession”.
  4. The first discovery of the M44 Beehive star cluster in the constellation Cancer. Ancient Chinese astronomers have also observed this star cluster, but they only saw a faint blue air mass, saying that it is “like a cloud but not a cloud, like a star but not a star, just seeing gas”. Hipparchus clearly pointed out that it was a cluster of stars, indicating that his eyesight was excellent.
  5. Observing the motion of the sun on the celestial sphere, and calculating that the length of a year is 365 1/4 days minus 1/300 days (365.2467 days), which is only 6.48 minutes away from the current 365.2422 days.

  6. Further observe the movement of the sun. He found that the solar annual apparent motion is not uniform, 94.5 days from the spring equinox to the summer solstice, 92.5 days from the summer solstice to the autumn equinox, 88.125 days from the autumn equinox to the winter solstice, and 90.125 days from the winter solstice to the spring equinox, a total of 365.25 days. Why are the seasons not evenly distributed throughout the year? Hipparchus thought that this may be because the sun’s orbit around the earth is not a perfect circle, which laid the foundation for Ptolemy’s “geocentric theory” later. Until the 17th century AD, the astronomer Kepler discovered the three laws of planetary movement, proving that the orbit of the earth around the sun is an ellipse, the sun is at the focus of the ellipse, and the eccentricity of the orbit is 0.017, revealing that the seasons are not uniform. the real reason.
  7. Observing the movement period of the moon, the period of the synodic month is 29.53058 days, which is only 0.00001 days away from today’s 29.53059 days; the perigee month is 27.55465 days, which is 0.0002 days away from the current measurement. How precious was this in the absence of precise instruments in ancient times!
  8. Observe solar and lunar eclipses multiple times. By observing the same solar eclipse from two places, he found that the distance of the moon is 30.167 times the diameter of the earth. The diameter of the earth measured today is 12,756 kilometers, and the average distance between the moon and the earth is 384,400 kilometers. The division of the two is approximately equal to 30.135, which is almost the same as Hipparchus’ calculation, which is admirable!
  9. Founded trigonometry and spherical trigonometry, which laid the foundation for astronomical calculations.
  From the above achievements, Hipparchus is worthy of being a great astronomer, and his name will always shine in the field of astronomy!