CHAPTER 1 THE BASICS OF ASTRONOMY ne of the oldest of all sciences is astronomy the study of celestial objects That s not too surprising since people have been looking up at the skies since before recorded history and peo ple who view dark skies quickly recognize that some of those points of light follow paths that are orderly and predictable Even though astronomy is one of the oldest sciences new discoveries continue to flood in from modern day astronomers Today of course astronomy has moved beyond merely observing the Sun Moon stars and planets from Earth s surface Today astronomy encompasses the study of everything outside our atmosphere from our solar system to the stars of our galaxy to all the millions of galaxies in deep space New technology new theo ries and new observations are leading us to ever more exciting insights into the astonishing complexity and diversity of Our universe 12
THE BASICs OF ASTRONOMY ASTRONOMY THROUGHOUT TIME The ruins of many ancient structures indi cate that their builders observed the motions of the Sun the Moon and other celestial bodies The most famous of these is prob ably England s Stonehenge which was built between about 3100 and 1550 BCE Some of the monument s large stones were aligned in relationship to the position of the rising Sun on the summer solstice Several hundreds of 11 1 The positioning of the stones in the prehistoric monument Stonehenge indicates that the site was used by ancient peoples to track the movement of the Sun and Moon George W Bailey Shutterstock com 13
ASTRONOMY UNDERSTANDING CELESTIAL BODIES other ancient structures showing astronomi cal alignment also have been found in Europe Egypt and the Americas In many early civilizations astronomy was sufficiently advanced that reliable calen dars had been developed In ancient Egypt astronomer priests were responsible for antic ipating the season of the annual flooding of the Nile River The Maya who lived in what is now southeastern Mexico Guatemala and Belize developed a complicated calendar system about 2 000 years ago The Dresden Codex a Mayan text from the 1st millennium CE contains exceptionally accurate astronom ical calculations including tables predicting eclipses and the movements of Venus In China a calendar had been developed by the 14th century BCE In about 350 BCE a Chinese astronomer Shih Shen drew up what may be the earliest star catalog listing about 8oo stars Chinese records mention comets meteors large sunspots and novae The early Greek astronomers knew many of the geometric relationships of the heavenly bodies A few early Greek thinkers includ ing Aristotle thought Earth was a sphere Eratosthenes born in about 276 BCT dem onstrated its circumference Hipparchus who lived around 140 BCTF was a prolific and 14
THE BASICs OF ASTRONOMY talented astronomer Among many other accomplishments he classified stars according to apparent brightness estimated the size and distance of the Moon found a way to predict eclipses and calculated the length of the year to within 6 5 minutes The most influential ancient astronomer historically was Ptolemy Claudius Ptolemaeus of Alexandria who lived in about 140 CE His geometric scheme predicted the motions of the planets In his view Earth occupied the center of the universe His theory approximat ing the true motions of the celestial bodies was held steadfastly until the end of the Middle Ages In medieval times Western astronomy did I not progress During those centuries Hindu and Arab astronomers kept the science alive The records of the Arab astronomers and their translations of Greek astronomical treatises were the foundation of the later upsurge in Ptolemy believed that Earth occupied Western astronomy the center of the universe Imagnol Hulton Archive Getty Images 15
