THE EVOLUTION OF ASTRONOMY SPACE
TABLE OF CONTENTS The evolution of astronomy 01 Ancient astronomy and astronomy in Islamic Civilization 02 Contributions of astronomers 03 The latest development in astronomy
TABLE OF CONTENTS
Aristotle Ptolemy Copernicus Brahe Galileo Kepler Newton HISTORY OF ASTRONOMY
Around 500 BC, most Greek believed that the Earth was round, not flat. ANCIENT ASTRONOMY The sphere of the world By the 5th century B.C., it was widely accepted that the Earth is a sphere. This is a critical point, as there is a widespread misconception that ancient peoples thought the Earth was flat. This was simply not the case. In the 5th century B.C., Empedocles and Anaxagoras offered arguments for the spherical nature of the Earth. During a lunar eclipse, when the Earth is between the sun and the moon, they identified the shadow of the Earth on the moon. As the shadow moves across the moon it is clearly round. This would suggest that the Earth is a sphere.
WHY DO BOATS DISAPPEAR OVER THE HORIZON? When a ship appears on the horizon it's the top of the ship that is visible first. A wide range of astronomy texts over time use this as a way to illustrate the roundness of the Earth. As the image suggests this is exactly what one would expect on a spherical Earth. If the Earth were flat, it would be expected that you would be able to see the entire ship as soon as it became visible.
MEASURING THE SIZE OF THE EARTH In 3rd Century B.C., Aristarchus of Samos reasoned he could figure out the size of the Earth based on information available during a lunar eclipse. The diagram at the right illustrates a translation of his work. Eratosthenes estimated Earth's circumference around 240 B.C. He measured the shadows cast in Alexandria and Syene to calculate their angle relative to the Sun. There is some dispute on the accuracy of his calculations as we don't know exactly how long the units of measure were. The measurement however was relatively close to the actual size of the Earth. The Greeks were applying mathematics to theorize about the nature of their world. They held a range of beliefs about nature and the world but they were, in many cases, working to ground those beliefs in an empirical exploration of what they could reason from evidence. The large circle is the sun, the medium circle is the Earth and the smallest circle is the moon. When the Earth is in-between the sun and the moon it causes a lunar eclipse and measuring the size of the Earth's shadow on the moon provided part of the information he needed to calculate its size. 1 lunar eclipses 2 Different approach
ARISTOTLE’S ELEMENTS AND COSMOLOGY In the tradition of Plato and Empedocles before him, Aristotle argued that there were four fundamental elements, fire, air, water and earth. Aristotle asserted that you could further reduce these elements into two pairs of qualities, hot and cold and wet and dry. The combination of each of these qualities resulted in the elements. These qualities can be replaced by their opposites, which in this system become how change happens on Earth. For example, when heated, water seemingly turns steam which looks like air. It is difficult for us to fully understand what this meant as today we think about matter in very different terms. In Aristotle's system there was no such thing as void space. All space was filled with some combination of these elements. 1 FOUR FUNDAMENTAL ELEMENTS
THE WANDERING AND FIXED STARS IN THE CELESTIAL REGION Looking at the night sky the ancient Greeks found two primary kinds of celestial objects; the fixed stars and the wandering stars. Think of the night's sky. Most of the visible objects appear to move at exactly the same speed and present themselves in exactly the same arrangement night after night. In this system the entire universe was part of a great sphere. This sphere was split into two sections, an outer celestial realm and an inner terrestrial one. The dividing line between the two was the orbit of the moon. While the earth was a place of transition and flux, the heavens were unchanging. Aristotle posited that there was a fifth substance, the quintessence, that was what the heavens were made of, and that the heavens were a place of perfect spherical motion. These are the fixed stars. They appear to move all together. Aside from these were a set of nine objects that behaved differently, the moon, the sun and the planets Mercury, Venus, Mars, Saturn and Jupiter each moved according to a different system. For the Greeks these were the wandering stars.
THE PTOLEMAIC MODEL By the time of Ptolemy Greek astronomers had proposed adding circles on the circular orbits of the wandering stars (the planets, the moon and the sun) to explain their motion. These circles on circles are called epicycles. To escape the complicated nature of this extensive number of circles, Ptolomy added a series of new concepts. To accurately describe planetary motion, he needed to use eccentric circles. Ptolemy then needed to put the epicycles on another set of circles called deferents. Ptolemy also needed to introduce equants, a tool that enabled the planets to move at different speeds as they moved around these circles. The resulting model was complex, but it had extensive predictive power. In the Greek tradition, the heavens were a place of perfect circular motion, so the way to account for perfection was with the addition of circles. This resulted in disorienting illustrations.
ASTRONOMY IN ISLAMIC CIVILIZATION More than 1200 years ago, astronomy gained a prominent place in the Islamic world, which stretched from the Iberian Peninsula to the Indian subcontinent. In this exhibit we highlight important contributions of astronomers and instrument makers from the Islamic world, while also highlighting current scholars and educators who study, cultivate, and share this important legacy.
FOLLOWING THE MOON This 16th-century illustration represents the celebration of the eid al-fitr, which marks the end of the fasting month, Ramadan. The religious practices of Muslims are regulated by the Hijrī calendar, a lunar calendar beginning with the migration of the prophet of Islam from Mecca to Medina in 622 AD. Since a lunar year is just 354 days long, constant calculations and observations are essential for determining important religious dates within Islam. Nowadays, Muslims combine traditional naked-eye observations of the crescent of the Moon, which signals the beginning and end of Ramadan, with nanosecond-precision level calculations made by astrophysicists.
TIME, FAITH, AND THE SUN For Muslims, determining the times of the five daily prayers requires observations and calculations related to the daily apparent motion of the Sun. These could be carried out in a relatively easier manner by using instruments such as the portable quadrant shown here. It was likely made in the 19th century in the Ottoman realm, which extended over the Balkans, Anatolia, the western part of the Middle East, Egypt, Algeria, and Tunisia. The basic design of this quadrant emerged in Northeast Africa between the 13th and the 15th centuries. Ottoman timekeepers continued to produce and use similar instruments well into the 20th century.
FINDING THE QIBLA This instrument is a qibla indicator from 19th-century Iran. The qibla is the direction to Mecca, which Muslims must face when performing their five daily prayers, wherever they are in the world. Finding the qibla requires an advanced knowledge of spherical trigonometry, but a qibla finder makes that operation easier. In this example, the lid contains a circular list of places with their respective qibla directions, called a gazetteer. After consulting the gazetteer, the desired direction could be found by using the instrument’s compass. Nowadays, Muslims use mobile apps that show a virtual compass and the direction to Mecca, in the manner of the old qibla indicators, but in digital format.
CONTRIBUTIONS OF ASTRONOMERS CLAUDIUS PTOLEMY (100 - 170 AD) He created a model of the solar system where Earth was at the center of all planetary rotation, and it's a model that has since been completely disproved.
CONTRIBUTIONS OF ASTRONOMERS NICOLAUS COPERNICUS (1473 - 1543) He was one of the first and most influential thinkers to create a "heliocentric" model of the solar system, meaning that he placed the Sun at the center of our planetary rotation
CONTRIBUTIONS OF ASTRONOMERS GALILEO GALILEI (1564 - 1642) A master of astronomy, physics, and engineering, Galileo contributed to our understanding of the universe in many different ways. Contrary to popular belief, he didn't invent the telescope, but he invented other scientific tools that he used to make celestial discoveries and observations.
CONTRIBUTIONS OF ASTRONOMERS CJOHANNES KEPLER (1571 - 1630) Kepler is also known for publishing several books that were used as the basis of Isaac Newton's theories on gravity. Overall, he's one of the most famous figures of the Scientific Revolution, so send him a few words of gratitude whenever you're looking at a star finder.
CONTRIBUTIONS OF ASTRONOMERS FREDERICK WILLIAM HERSCHEL (1738 - 1822) Herschel's career-defining moment was discovering Uranus in 1781. However, his legacy was all about telescopes. He spent years carrying out "star surveys" to track celestial objects, eventually building and customizing his own tools to see them more clearly.
THE LATEST DEVELOPMENT IN ASTRONOMY A lot is going on around us in the space. Every day, space centres worlwide make discveries and breakthroughs by decoding some strange signals from the nearby stars or launching new rockets into the geostationaryorbits.
Recently, scientists have received some strange narrowband signals from the nearest star to the Earth- the Proxima Centauri. The wavelength recorded was around 982.002 MHz, which is indeed very weird because stars and other heavenly bodies usually emit broadbandsignals. NEW STRANGE SIGNALS RECEIVED FROM PROXIMA CENTAURI 01.
The significant conjunction- where both Jupiter and Saturn will appear as single planet in the sky is a miraculous astronomical event in the past 400 years. The planets will be so close to each other they the conjunction will appear to be the brightest star in the sky, as can be seen from the ISS space station live feed JUPITER AND SATURN TO COME CLOSET TO EACH OTHER IN HISTORY 02.
The new solar telescope- DKIST- has provided us with a brilliant picture of the sunspot, the first of its kind. The image is captured with very high resolution, and that’s why the sunspot has a diameter of around 16,000 km in the original picture. THE FIRST IMAGE OF SUNSPOTS CAPTURED WITH A NEW SOLAR TELESCOPE 03.
The fast radio bursts are nothing but high energetic pulses usually received from a far-of distance in space but only for some time because evaluating those signals has been difficult. For the first time, scientists have received radio bursts from within the Milky Way Galaxy, which is a wonder in itself. FAST RADIO BURSTS RECEIVED FROM WITHIN THE MILKY WAY GALAXY 04.
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