The 2014 National Science Olympiad Astronomy Event Part 6

Astronomy 2014 – Part 6 The stellar radiation laws and blackbody radiation have been a part of every past Astronomy event. A blackbody is an artificial construct that absorbs all radiation it receives and then emits it all away – everything that comes in goes out. Stellar atmospheres are very good blackbody radiators, absorbing radiation produced by the core and emitting it out into the interstellar medium. The hotter the star the more energy it emits at every single wavelength than a cooler star. The graphic shows a 12,000K star, a 6,000K star and a 3,000K star and nowhere does the 3,000K star emit more radiation at any wavelength than the two hotter stars. That principle is called Planck’s Law. Wien’s Law states the maximum radiation that comes from any star or blackbody has a peak with a specific temperature and corresponding wavelength. The mathematical relationship is used to determine the temperature and/or wavelength of stellar objects. This next graphic shows stellar bar codes with absorption lines and also the blackbody curves of the IR, visible, and UV parts of the stellar spectra. This spectra is the optical portion only of the total radiation produced by the Sun. There are several absorption lines – which shows the elemental composition of the Sun. The typical spectral images shown in textbooks are gross cartoons of a stars total emission. The two lower images show spectral plots – wavy lines with dips to show where absorption is happening. Stars are classified by their spectra – and their spectra are the result of their temperature. Spectral images look like bar codes, and the spectral plots are more useful of scientific measurements. Hydrogen Balmer lines and the Fraunhoffer lines from other elements are used for classification and each stellar temperature has a unique set of absorption spectra. The radiation laws include three relationships; Plank’s law, Wien’s law, and Stephan-Boltzmann’s law. Stephan-Boltzmann’s law is a measure of the power of a star and is equal to the area under its blackbody curve. The radiation laws and the basic mathematical relationships and equations shown are the most important to understand for this event. For resources, the Astronomy Coach’s Manual is available from the National Science Olympiad online store. The Astronomy Picture of the Day (APOD) website is a good place to find and collect images. Search the archive for the DSO’s, and the first page of images will show images in all wavelengths. The Chandra website Photo Album has information and images for many of the DSOs. The Chandra website has a variety of excellent stellar evolution materials and resources to help learn about stellar evolution – including the webinars. The AAVSO website is also a valuable resource. The 2012 and 2013 events and answer keys are posted to download and use for practice. The webinars as well as the accompanying PowerPoint presentations are posted there as well. The Coaches Clinic PPTs are posted as well as flash cards to be downloaded and used to learn to identify the DSOs. The Variable Star Astronomy curriculum has chapters that give detailed explanations of variable stars, light curves, phase diagrams and O-C diagrams. The Chandra website contains online tutorials, flash versions of stellar evolution to practice evolutionary sequences, web quests, and additional activities and investigations to prepare for the Astronomy Event. Teams that have questions about the event description access the rules clarification link on the NSO website. This is the place to post questions about clarification issues – the event description and/or resources. Before you post your question check to see if someone has already asked that question and it has been answered. If no one has posted that question yet, then post it and you will be sent an answer. This way if more than one team has the same question, then the answer is already posted when they access the website. To prepare for the event read the event description; know exactly what the allowable resources are as you do not want to be disqualified or have to leave your resources outside the room because they do not meet the permissible resources. Watch this webinar and the PowerPoint for an overview of the DSOs and basic content. Use the Astronomy Coaches Manual as a guide for how to collect the images and information for 2014 competition. Use the Chandra, AAVSO, and APOD websites. Download the 2012 and 2013 Astronomy events from the AAVSO website for practice and use as a guide to possible types of questions. The Astronomy event has the same format every year.