Searching Space and the Solar System: How We Know Facts About the Sky

When you look at the sky in the daytime and at night, you do not have to be enrolled in an astronomy class to be enthralled the mechanics of it. There is an endless amount of aspects in which we can study to better understand the sky under which we reside. One of the first early questions about the Earth in relation to the sky was whether the Earth was flat or round, and how the sky and stars surrounded us. If you look out across a field or a large body of water, it seems to be flat, but the curve if the Earth is obviously not. No matter how hard you tried to reach the end of the world and thus fall off, the early scientists claimed, you could never do such action. Not all of these scientists and philosophers were completely wrong. Take for example Ptolemy; he pondered the location of the sun to the Earth and determined a geocentric viewpoint. We know that the solar system is heliocentric now, but how did new information relating to Ptolemy's work change views? Proving that the sun was the center of our solar system instead of the Earth took thinkers and knowledge of the surroundings. For example, Copernicus found accurate relative distances by calculations. Still to this day, we use epicycles on the perfect circles at constant speeds to determine irregular planet motion. With today's technology though, we can clear up some misconceptions and find new information every year. We have concluded evidence on the Earth and its size, the moon, the solar system, stars, etc.

I had just claimed the Earth to be round, as most likely every other person would, but that statement needed proof in order to be trusted. As the early astronomers began to realize the actually shape of our planet, the next step is to figure out the size. Eratosthenes helped to aid this idea by realizing and recognizing the sun's position. Not only finding that fact that Earth was rounded, but finding the diameter and size was equally as difficult and profound. By using measurements, he used a messenger to help collect data. As we discussed in lecture, he was only off the actual circumference by 15%, an amazing feat by someone in that age of his technology. Today, we take many aspects of astronomy for granted. For example, everyone knows that the Earth moves and at a great speed. Again, it took many years to be sure and clear about how this works. We first gathered this information from pendulum, which concluded that it is the Earth that moves, and not the sky around us. The first pendulum was built in Paris by Leon Foucault. By using an iron weight and cable, he swung it toward a star and showed that the plane of the swing rotated to the right. Pendulums such as this, known as the Foucault pendulum, are used around the world and are quite interested.

The moon is a great, interesting body of rock in our orbit. For thousands of years, the early societies and cultures were propounded by the moon and the logistics of its nature. Today, we know what the moon consists of and how far away. For example, it takes only one second for light to reach the moon from Earth. It takes approximately one month to orbit our planet and it has daily paths similar to that of the sun. We understand the distance to the moon by an effect known as a parallax. This is used by angles and different points in relation to each other. By using this type of measurement, we gather data and know that the moon is about 250,000 miles from our planet. With powerful equipment such as telescopes, we can view many spectacular things in our solar system. We knew that planets exist for a long time, but how could we see them and have a better understanding than what our eyes showed us? As I said previously, the powerful technology aids us in finding beautiful things, such as the information about the surface of Venus. We have resources, such as the Russian Venera Landers, to help us gather this data. By using radar imaging also, we can study this planet from probes and from Earth. The Magellan orbiter, which took about four years, allowed us to gather very detailed pictures of its surface. From these pictures we have concluded is rather smooth and also contains volcanoes, canyons, and other such things found here on Earth.

If we were to ask someone 2000 years ago, and a child today, what the most fascinating thing at night in the sky would be, the answer would most likely pertain to the stars. Since the dawn of mankind, we have witnessed the stars but had little knowledge of how the mechanics played out. Since then, aspects such as star heat, location, size, and movement of the stars is covered in any astronomy text book. There are many equations that help us figure out these questions and helpful techniques that assist us. Take for example; when we determine a star's distance, we measure its parallax. That star's parallax is measured in seconds of arc and is defined as half the total angular shift. The equation for this is d(pc) = 1/p^p where p stands for the star's parallax, d for the distance of the star, and pc as the measurement of parsecs. As I have said, equations such as the previous are essential. Other equations such as the velocity equation (which uses parts such as space velocity and radial velocity) helps us determine the tangential velocity. Ideas such as the Doppler Effect come into play and explain what we see in the sky. This brings us to the next interesting topic, the brightness or magnitudes of the stars. We classify stars on their magnitudes, smaller numbers in the classification being brighter. We classify them by their apparent magnitude because they are the brightest in the sky. We used to measure this by eye, but no longer do. The classification by eye was known as the apparent visual magnitude. Astronomers now use the absolute visual magnitudes, which is defined as the apparent magnitude a star would have if it were placed at a standard distance of 10 pc. Again another equation is used, known as the magnitude equation (M = m+5-5 log d) to determine this. The apparent and absolute magnitudes are also contained in this equation. By the classification, we know how bright one star is from another. As the example from class stated; a star with a magnitude of 5 is 6.3 times dimmer than a star with a magnitude of 3. (3 to 4 to 5, thus 2.512 x 2.512 = 6.3) As the example showed, each number or step between magnitude classifications is 2.512 times that of the next. Size and heat of stars is represented by the Hertzsprung - Russell diagram, which is said to be the most important took of stellar astronomy. There are different qualifications in this diagram, from dwarfs to super giants. A dwarf is defined as stars of the main sequence on the Hertzsprung - Russell diagram. Super giants are known as huge, luminous stars on top of the diagram. From the lecture, we know that the larger super giants do not last nearly as long as the dwarfs. We find stellar diameters with that of the sun by luminosity and radius, along with the determination of luminosity classes from before. The movement, size, heat and brightness of stars today are now simple to calculate.

'We cannot treat stars simply as individuals. We muse also deal with their collective behavior, which ultimately tells us a great deal about them.' (pp. 357) There are so many interesting qualities of stars, such as the elements that they are made of and the interstellar gas. For example, our sun is made up of mostly hydrogen (75%) and helium (25%). There are constant reactions and movement, using up these elements, but contains so much matter (about 99.8% of all the mass in the solar system) is it not a significant amount from day to day. The sun still has about half of its life left, around another 5 billion years. Stars are formed from interstellar clouds. These clouds are created by dust cloud and gas that orbit in our galaxy. Gas clouds are mostly hydrogen and helium, just as the stars. The atoms of the gas are very cold and do not create too much energy, which can result in the formation of clusters. Today, we believe that formation of a star from interstellar gas clouds takes several stages to complete. Clumps heat up and forms into a disk shape. It is said that it takes approximately one million years to form in a protostar, which will later form into a main sequence star on the Hertzsprung - Russell diagram. As I have said earlier, equations, new technology and knowledge will constitute for a deeper knowledge and answer the question; "How do we know facts about the sky?" more clearly.

Sources:

1) Kaller, James. Astromony!. New York: Addison-Wesley,

2) "The Surface Features of Venus." 24 Apr 2007 .