This unit is designed for students who attend an alternative high school program because they have had poor attendance and behavior problems, resulting in a lack of sufficient high school credits to graduate. These students have not had much success in school. Therefore, when a curriculum is created for them, several facts must be kept in mind. Realities, in terms of numbers and mathematics, are difficult for them to visualize, comprehend, and express in meaningful terms.
This curriculum was developed in collaboration with an English teacher. This unit will integrate two disciplines, English and Math and will be co-taught. The two teachers will introduce several mathematical and scientific concepts, making connections between and among science, math, history, and English. The approach will be interdisciplinary, supplemented by readings, films, and activities using the scientific method. Since classes at this high school are integrated (grades 9-12), we will team teach the class, seeking to improve student performance and skills at all levels.
The curriculum is designed so that each student in the class can feel at ease as s/he is motivated to learn more about where we are in relation to the Milky Way. Each student will play a special role in developing his or her talents with specific objectives in mind. As students are stimulated, our roles will reverse. They will become "teachers," and teachers will become the "learners." Students will guide and be guided through as series of group activities using a scientific approach.
Students' interest in astronomy and their understanding of the cosmic landscape will be stimulated by readings, both assigned and suggested. Students seem to be aware of what astronomy can offer to the human perspective, but are often unaware of the methods of science, including procedures and required rules. Hence, they look for "quick answers," seldom thinking or realizing that there is a process that leads toward a clearer understanding of the structure of the cosmic landscape.
Students will realize and understand that communication gaps develop as scientists become thirsty for knowledge about new frontiers. This gap leads people to all manner of unbelievable and unreliable sources for information-especially in new areas of inquiry. The media is an excellent example of misinformation and pseudoscience. By a rational, not an irrational or haphazard process, and through the interdisciplinary approach, students will be able to probe the cosmic landscape's many mysteries.
The main focus of this unit will be to determine where the earth is located in our solar system, and where the solar system is located in the Milky Way Galaxy. One of the many goals will be to give the students a sense of where they fit in this astronomical universe-a sense of location in the cosmic landscape, based on mathematical calculations
Students will compare the positions of the nine planets and sun, starting from earth, our home planet. When we consider sizes and distances in space, the goal will be to have students think "cosmically." As part of this mathematical comparison, students will review and practice the concept of scientific notation. The sheer size of the universe and the immense distance involved almost defy human understanding and experience. We live in a very thin layer on a small planet: our solar system comprises less than a speck in our Milky Way Galaxy, less than a grain of sand on an immense beach. Our solar system is almost invisible on the scale of our Milky Way Galaxy. Our galaxy is only a pinwheel of light in an enormous, expanding universe.
OVERVIEW OF THE MILKY WAY
On a dark cloudless night, you can see a faint band of light, stretched with stars and reaching across the sky. It was said that the ancient Hindus thought of this dim white glow as milk splitting the night sky; hence, they called these stars the Milky Way. Now, in the twentieth century we know that these stars, along with our Sun, form a huge, slowly revolving disk--our galaxy. The word "galaxy" itself comes from the ancient Greeks and their word for "milk,"--galactos. Thus, "Milky Way" is both the name of the band of light across a clear night sky and also the name of our galaxy.
Our earlier understanding of the Milky Way dates back to the 1800's Thomas Wright, an English astronomer, and Immanuel Kant, a German philosopher. Wright, by counting the number of stars visible in different directions, concluded that the solar system was near the center of a spherical cloud of stars rather than a flat disk, as had been suggested by Immanuel Kant. Because Wright thought the Milky Way was spherical, he thought the stars would lie in all directions of the night sky.
Today, it is inarguable that the basic shape of the Milky Way is a spiral flat disk. For instance, a budding astronomer can go outside on a clear night and see that there are vastly more stars in the direction of the Milky Way than there are stars in any other direction. If the Milky Way had a spherical shape, one would see about the same number of stars in every direction of the night sky. However, since it is a flat disk, one sees that stars are concentrated into the band which makes up the Milky Way. Kant further proposed that the Milky Way galaxy can be used to compare other existing galaxies. For example, it was assumed that every galaxy was shaped as a flat disk. In addition, the surface brightness of galaxies seemed fairly low, through observation of faint stars which appeared to have a relatively uniform lack of volume of light in the Milky Way.
Wright's inconclusive argument was further redefined toward the end of the 18th century by an English astronomer named Sir William Herschel. Herschel incorrectly concluded that the Sun was the center of the Milky Way. Herschel did not have a method to measure distances to the stars, so he could not determine the Milky Way's size; Therefore, it is known that he was led astray because he did not know that dust clouds mask out distant stars and prevent us from seeing our galaxy's actual shape and size.
The size of the Milky Way was first measured in the early 1900's by a Dutch astronomer, Jacobus C. Kapteyn and the American astronomer, Harlow Shapley. Kapteyn used Herschel's method and added his own data, strengthened by his knowledge of distance to nearby stars. Kapteyn measured the distance to nearby stars by a scientific method called stellar parallax, or a change in an object's apparent position caused by a change in the observer's position. A familiar example is easy to demonstrate. Even a novice astronomer can hold his or her hand motionless at arm's length and close one eye to observe what seems to be a shift in the position of his or her finger. Repeating this exercise, now closing the other eye, causes the finger to appear to move against the background, although, in reality, his or her eyes have the changed the viewing position, and the finger has remained stationery.
This at-home demonstration helps us understand how parallax gives us the ability to see things three dimensionally. When we look at something, each eye sends a slightly different image to the brain, which then processes the pictures to determine the object's distance. To observe stellar parallax, astronomers take advantage of the Earth's motion around the Sun. They observe a star and carefully measure its position against background stars. They then wait six months--until the Earth has moved to the other side of its orbit--and make a second measurement. As a result, the star's position has changed, observed in comparison with the background stars. The angular distance that a star's apparent position changes depends on its distance from us. Although the change is larger for nearby stars than it is for more distant stars, the angular distance is extremely small for all stars. In fact the distance is so insignificant that that it is measured, not in degrees, but fractional degrees called "arc seconds."
A star's parallax (p) is defined as related to half of the degrees of angle created when the star changes position. Using that definition for parallax (p), the star's distance, (d) can be calculated using 1 / p, if we measure (p) in arc seconds, and (d), not in kilometer or light years, but in a new unit called "parsecs". This word comes from a combination of "parallax" and "arc seconds." There are 3,600 arc seconds in one degree.
Kapteyn's method of parallax, unlike Herschel's, was thus able to reasonably determine preliminary dimensions of the Milky Way. In total, the thickness of the Milky Way was found to equal 2,000 parsecs and have a diameter of 10,000 parsecs. However, almost immediately after Kapteyn's publication of his model of the Milky Way, an American astronomer, Harlow Shapley, published a model in strong opposition. Shapley argued that the Milky Way was larger than what Kapteyn had calculated and that the Sun was not near the center, but about two-thirds of the way out in the flat disk. Shapley defended his theory from a unique study of globular star clusters--dense groupings of up to a million stars.
Globular clusters have so many stars that they are very luminous and can be seen from great distances across the galaxy and beyond. Many of the clusters lie above the flat disk, so a clear view of them is quite apparent. At the time, Shapley knew that the evidence to support his model would be found by mapping the distribution of globular clusters. This would provide a more accurate representation of the Milky Way that had ever been achieved. To make up this map, Shapley needed to know the distances of the globular clusters from the sun. He could measure these distances by observing variable stars, those that change in brightness. Measurements were determined using the Standard Candle Method to calculate the distances to variable stars called "Cepheids."
Shapley took pictures of stars and compared their true brightness (B) to find the distances to those stars. Once again, even a novice astronomer can look at an object of known brightness and estimate its distance from how bright it appears. For example, while driving at night, one's life depends on making distance estimates of the lights of oncoming cars. The Standard Candle Method is just a more refined method to determine distance.
Hence, Shapley found globular clusters ranging 30,000 ly away. He also found other clusters further away which had a variety of angular sizes (physical shapes). Drawing his conclusions from the globular clusters, Shapley determined the shape of the Milky Way. But Shapley overestimated the Milky Way's diameter, and proposed that its size was approximately three times greater than was formerly accepted.
Shapley was able to determine the distance to the closest globular clusters. Shapley measured angular diameters of globular clusters of known distance, thus obtaining their true diameters. Assuming a statistical average for the true diameter of the clusters, he was able to then obtain distances estimated for the remote ones from their observed angular diameters.
From their directions and derived distances, Shapley mapped out three-dimensional distribution in space of 93 globular clusters. He found the clusters formed a spheroidal system. The center of that spheroidal system was s point in the middle of the Milky Way and a distance of some 25000 to 30,000 ly. Shapley then made a correct assumption that the system of globular clusters is centered in the center of the galaxy. The sun lies far from the galactic center, the main disk of the galaxy probably extends a nearly equal distance beyond the sun and comprised a gigantic system, which is at least 100,000 ly across. Today the center of the galactic nucleus is estimated to be 8,000 pc from the sun.
Over the last 50 years, astronomers have revised and improved Shapley's model of the Milky Way. Given that the Milky Way is a flat disk and that other disk galaxies have spiral arms, astronomers have generally concluded that the Milk Way consists of several parts: It is a flat disk that is about 25 kilo parsecs in diameter. It has a halo that surrounds the disk, much as a bun surrounds a hamburger. There is a bulge where the central parts of the disk thicken. Within the disk, numerous bright young stars cluster into spiral arms that wind outward from near the center. Our Solar System lies between two arms about 8.5 kiloparsecs from the center. The orbits of the planets are tilted by about sixty degrees in respect to the galaxy's disk. This tilt is the reason why the band of the Milky Way on the sky is tipped with respect to the elliptical path that the sun follows.