Second in a two-part series about stars and how we classify them. Beginning with the lifecycle of stars, which is what classifying stars is all about, I then talk about the various ways we've chosen to interpret observational data on stars, from observing the bright sky-dots to evaluating how bright they are by comparing them to each other, and all the new things we can do with CCD imaging. Hear about pre- and post-telescope star catalogs and especially hear about Annie Jump Cannon and how she formed the basis for the star catalog standard we use today.

First in a two-part series about stars and how we classify them. Variables are a very specific kind of star that have a regular variation in brightness, like a heartbeat. They were first categorized and analyzed by Henrietta Swan Leavitt at the turn of the 20th century at Harvard University, along with other women computers at the time. Leavitt noticed variable stars in the Magellanic Clouds and came up with her luminosity law, where the pulse rates of Cepheid variable stars are proportional to their luminosity—the brighter they are, the greater their period is. This law helped estimate interstellar and intergalactic distances. Cepheids and other kinds of variable stars have helped astronomers map out the size of our galaxy, the spaces between celestial objects, and the distance to the outer reaches of our universe.

Henges are only one type of astronomical tracking and observation monument. Other kinds include using big rocks that already exist and then building something close enough to observe its interaction with the Sun; building an observatory or a big pyramid; constructing something that interacts with the sun in a very quiet, private way; or hauling a big heap of strange rocks in the middle of the chalk uplands of England (hello, Stonehenge!). Hear me read a bunch of quotes from archaeoastronomers about what their profession is, too!

Different kinds of telescopes and 19th-century photographic techniques demonstrate far more vividly than mere words can convey that taking photos of space is VERY hard, but the Hubble Space Telescope is doing it well at age 27! This episode talks about how we got to where we are with cosmological photography. And then there’s the James Webb Space Telescope going up in 2018... Bonus supermassive black holes, and yes I mean the Muse song.

Learn about some of the major cosmological models that scientists through the ages have assigned to our universe, even when the known universe was only as big as our solar system. I talk about Claudius Ptolemy, Al-Hasan Ibn al-Haytham, Nicolaus Copernicus, *dreamy sigh* Tycho Brahe, Johannes Kepler, Galileo Galilei, Giordano Bruno, René Descartes, Sir Isaac Newton, Pierre-Simon Laplace, Albert Einstein, Edwin Hubble, and finally the most common cosmological model accepted today (because it wouldn't be current science if everyone agreed on it).

Welcome to the first episode of HD and the Void, space edition! Start at the beginning of the universe with the Big Bang, then zoom to the beginning of records of humanity's astronomical observations with the Mesopotamian star chart MUL.APIN. Bonus fun facts: cosmic microwave background radiation, star catalogs, the constellation Triangulum, different kinds of calendars (solar, lunar, and luni-solar) and how to use constellations or seasons to track them, goat-fish, and retrograde motion.