Earth Science / Astronomy Ptolemy

Earth Science / Astronomy

Ptolemy focused on a series of earlier ideas when he devised his theory regarding the geocentric movement of the planets. The theory emphasized the fact that the Earth was stationary and at the center of the universe. All the objects in the universe were believed by Ptolemy to revolve around earth. The Greek astronomer observed that the celestial bodies appear every day in the same place they did a day before and that the Earth appeared to be at rest because of its presumed stability. This theory contributed to the belief that the Earth was spherical, not flat as most people formerly believed.

The Earth performs a complete revolution every twenty-four hours, relative to the sun. Every year the Earth revolves around the sun, this motion lasting for approximately three hundred and sixty five days. The Earth performs a complete cycle of precession once in approximately 26000 years, with the current angle between its rotational axis and the plane to its trajectory being 23.44 degrees.

Q3. Nicolaus Copernicus is responsible for devising a reasonable heliocentric theory. Tycho Brahe was a Danish astronomer who devoted his life to studying astronomy and the movement of the planets, bringing large contributions to the field of astronomy and providing his assistant, Johannes Kepler, with information which the latter used in developing the laws of planetary motion. Kepler's studies were essential in assisting Sir Isaac Newton in devising the theory of universal gravitation. Galileo Galilei lived contemporary to Kepler, with the latter mentioning a series of the former's achievements for astronomy, namely the confirmation of Venus's phases and the finding of Jupiter's four largest satellites. Galilei is also responsible for perfecting the telescope.

Q4. There are eight planets in the solar system, Mercury, Venus, Earth and Mars are referred to as "terrestrial planets" while Jupiter, Saturn, Uranus and Neptune are called "gas giants." The terrestrial planets are mainly composed out of rock and metal whereas the gas giants are principally made out of water, ammonia, and methane. The terrestrial planets are much smaller than the gas giants. There are also other planets in the solar system, with Pluto, Haumea, Makemake, Eris, and the asteroid Ceres representing the system's dwarf planets, which do not comply with all the requirements necessary for a celestial object to be classified as being called a principal planet in the solar system.

Q5. Stellar parallax is the phenomenon through which one can approximate the distance to a celestial object by observing the position of an object in the universe at different times in the year, the measuring tool most often used to do this being a heliometer.

Q6. Earth only has one natural satellite, the Moon. It is only surpassed by five other satellites in the solar system when considering its size, the largest satellite in the solar system in comparison to the size of the planet it revolves around, and the second densest satellite in the solar system. The lunar maria are dark areas on the planet's surface which are a result of volcanic eruptions. Their darkness is owed to the fact that they are based in plains, making them less reflective than the higher areas, which contain less iron. The moon's surface is filled with craters and most of them are a consequence of impacts. The term was first used for the depressions on the moon's surface by Galilei, who supported the theory that the moon was not a perfect sphere. Craters differ in size, with the smallest being microscopic and the largest being approximately 200 miles in diameter. Lunar maria were associated with craters, some individuals promoting the belief that the dark areas on the moon are actually craters that were filled with lava consequent to the impact. The soil on the moon is also recognized as regolith, given that it complies with the term's characteristics of being heterogeneous found on top of solid rock. Unlike the soil on earth, lunar soil does not contain moisture and air. There are several theories on the topic of the moon's origin, but none can be verified for validity. The Moon is believed by many to have been part of the earth and that it was tore off as a result of an initial spin that was too great to hold the planet together. One of the prevailing theories was that involving an impact of large magnitude involving the newly formed Earth and a giant object of the size of Mars hitting Earth and blowing up material that later formed the moon.

Q7. Astronomers mainly use the Hubble galaxy classification system when trying to recognize a particular galaxy as belonging to a particular type. The system was created by Edwin Hubble in the twentieth century, as the American Astronomer came up with three groups through which one could classify any galaxy in the universe. Elliptical galaxies look like ellipses, light being distributed evenly. Spiral galaxies are similar to Elliptical galaxies, but they differ through the fact that they are composed from a flat disk, with stars composing a structure similar to a spiral and involve a middle concentration of stars, which makes this type of galaxy look like an elliptical galaxy in its center. Lenticular galaxies resemble spiral galaxies to a large degree, but they differ through the fact that they do not look like a spiral and their disks from a limited quantity of stars.

Q8. A star's life cycle contains the following steps: protostar formation, main sequence, and post-main sequence. Stars are initially formed into a high concentration Nebula; they later condense in large spheres of gas and decrease because of their own gravity. Parts of condensed matter heat up and create protostars. The energy released by the celestial object causes it to stop contracting more energy and it begins to shine as a result, becoming a main sequence star. The main sequence lasts for approximately ten billion years, the period it takes for all the hydrogen to fuse and form helium. The helium later fuses and forms carbon and light gradually loses intensity, turning into an expanding star called the Red Giant. When the helium runs out the core is about 80% from the star's original size cools and loses intensity, becoming first a White Dwarf and later when it seizes to shine becoming a Black Dwarf. In the case of a Massive Star, the stars become Red Supergiants the moment the hydrogen ends, causing nuclear reactions to take place for the following three million years. The Massive star's core then collapses, causing an explosion also known as a Supernova, blowing shock waves through its surface.