The formula for collisional excitation of the atoms responsible for auroral emission can explain why green auroras from excited oxygen atoms can occur at relatively low altitudes, but red auroras from these same atoms are constrained to higher altitudes of lower density. The same formula also suggests much lower electron velocities (~100 km/s) than are required to excite the oxygen atoms to the required metastable levels for subsequent emission (~1000 km/s).
...What we have come to appreciate is the seminal role played by clustered star formation in driving the physical and chemical evolution of the galaxies that host these stellar nurseries. Such concentrated sites of newborn stars along with their nebular environs constitute what are known as galactic ecosystems. These energized realms represent vital “crucibles” for growing the chemical complexity that is necessary for biotic processes.
Carl Sagan wrote that "If you wish to make an apple pie from scratch, you must first invent the universe.” We wish to know our home, so back we go, to the Big Bang, and step by step to today.
This edition combines fun and science as only Dr. Waller can do, as we take a colorful look at what's going on in supposedly empty space between the stars in the Milky Way galaxy.
This January, the American Astronomical Society held its big annual meeting completely online. The Covid-19 pandemic ruled out the society’s planned gathering in Scottsdale, AZ but the AAS pivoted by opening-up digital access to thousands of astronomers across the United States and around the world. More than 3,000 registrants were listed in the online portal, thus demonstrating that the vital communication of astronomical research, education, and public outreach could carry on in this alternative format.
If the Big Bang theory is correct, how fast is the universe expanding? Astronomers are facing a troubling disconnect between different methods used to measure the expansion rate, known as the Hubble constant. The two methods are giving similar but slightly different rates. Either one method is providing inaccurate results, or there is some kind of unknown physics operating in the universe.
