Dark Matter essays

Dark Matter essays Two people have been credited for determining the need for dark matter. The first was astronomer Jan Oort, who back in 1932 measured the perpendicular motions of nearby stars relative to the disk of our galaxy. By studying the gravitational influence of the disk on these stars he was able to calculate the mass of the disk. The value he determined was twice as much as that inferred by the visible stars and nebulae in that region. A year later in 1933 astronomer Fritz Zwicky estimated the mass of a group of galaxies by measuring their brightness. When Zwicky used a different method of calculating the mass of the cluster he found it to be 400 times the value from directly inferring the mass from the brightness of the cluster. In both cases Oort and Zxwicky came to the conclusion that the visible galaxies only accounted for 10% of the mass needed to keep them gravitationally in the cluster. Based on 70 years of accumulated observations of the motions of galaxies and the expansion of the universe, most astronomers believe that as much as 90% of the stuff constituting the universe may be objects or particles that cannot be seen. In other words, most of the universes matter does not radiate it provides no glow that we can detect in the electromagnetic spectrum. Now in the 21st century, Zwicky and Oorts theories have been further enhanced. We have already observed in clusters of galaxies that the motion of galaxies within a cluster suggests that they are bound by a total gravitational force due to about 5-10 times as much matter as can be accounted for from luminous matter in said galaxies. But it is also theorized that within an individual galaxy, you can measure the rate of rotation of the stars about the galactic center of rotation. The resultant rotation curve is simply related to the distribution of matter in the galaxy. The outer stars in the galaxies seem to rotate too fast fo...

Infographic How to Apply for College, Step by Step

Infographic How to Apply for College, Step by Step SAT / ACT Prep Online Guides and Tips The college application process can be a long and difficult journey for high school students. Organizing your application materials well in advance and paying attention to deadlines is critical. You should also start researching colleges earlier rather than later so that you can account for each school's specific application requirements. In this infographic, I've broken down the actions you need to take to be prepared for college applications starting at the beginning of your junior year through to your senior spring. Applying to collegeisn't as intimidating as it might seem! There are certain basic steps you will need to take beginning in your junior year. Ideally, you should take the SAT or ACT for the first time your junior fall to give yourself plenty of time to improve your scores before you apply to college. The early to middle part of junior year is also the best time to begin researching colleges. This ties into potentially retaking the SAT or ACT if you find that the colleges that interest you are looking for higher scores. In the spring of your junior year, it's a good idea to ask teachers if they are willing to write recommendation letters for you. Asking for letters early on will ensure that the teachers you've chosen are on board, and the letters themselves may turn out better since your teachers will have more time to think about what they want to say. In the summer before senior year, you can make your final college list and start looking at the specific requirements for each school. This is also a good time to prep for your last chance at standardized tests and begin thinking about your college essay. You should write a first draft of your essay in the summer so that you won't have to worry too much about it during the school year. When you're trying to fill out applications and manage your classes at the same time, the essay can seem like an overwhelming responsibility. Once your senior year starts, you should submit formal requests for recommendation letters to the teachers who agreed to write them for you in the spring. If you're planning on taking the SAT or ACT one last time, your final chance will be in October or November if you're applying early decision. Most early action and early decision applications are due by November 15th, and you will get back the decisions about a month later in mid-December. Regular decision applications are typically due around January 1st, but colleges have different policies for how late you can submit your SAT or ACT scores. Often, students are permitted to submit scores from tests taken as late as February, but make sure to look up schools individually to see what's allowed. You should be notified about the status of your regular decision applications by late March.All that's left after that is to choose your favorite college out of the schools where you were accepted. This might be the hardest part of the whole process (but in a good way)! What's Next? Are you interested in highly competitive colleges? Find out more about the most selective schools and how to ensure that you have the best chance of being accepted. If you're struggling to start writing your college essay, read this article to learn which prompt you should choose and how you can being the brainstorming process. Extracurricular activities will be an important aspect of your college application. Find out more about extracurriculars and why you should have them! Want to improve your SAT score by 240 points or your ACT score by 4 points?We've written a guide for each test about the top 5 strategies you must be using to have a shot at improving your score. Download it for free now: