Spectroscopy, which can identify objects via unique combinations of so-called “spectral lines,” can also be used to measure velocity, thanks to the Doppler effect. Leavitt used the “identification” properties of spectroscopy to find her law, but to find...
By the early 20th century, it was possible to see and measure a very different Universe than was accessible to the Ancients, or even to Galileo and Newton. It had many more stars, and it had beautiful collections of stars (then called “nebulae”) with...
In the 19th century, photography and spectroscopy entered astronomy, and ultimately changed everything. Long-exposure photographs revealed scores of beautiful nebulae and millions of previously unknown faint stars.
Spectroscopy showed clear evidence...
While thinkers prior to Hubble’s era disagreed on whether the Universe was infinite (Anaximander) or finite (Olbers), they essentially all agreed that it was unchanging (Aristotle) at some great distance from Earth.
Even during the Renaissance, which...
Of course, these two tricky questions can be avoided if a supernatural power pressed a "start" button on time, and controls whatever is "beyond" our Universe. In Ancient times thinkers across cultures believed the Universe was controlled at least in...
A wide variety of modern astronomical observations clearly show that our Universe had a beginning in time, known as the “big bang.” But, those same observations also show that the Universe expands in all directions simultaneously, meaning that it has no...
