Throughout history, determining the size of the solar system was a long-standing problem. Nearly two millennia ago Aristarchus measured the angle between the Moon and the Sun when the Moon was in its quarter phase (when half of it is illuminated from the Sun), and used trigonometry to determine that the Sun was about 20 times further away than the Moon. Some time later, Hipparchus used the parallax of the Moon to determine the Moon was about 60 times the radius of the Earth. These results weren’t particularly accurate, but they were the best to be had until at least the 1400s.
Welcome to the Future
With the dawn of 2015, there’s been a lot of references to the Back to the Future series. The original movie is now as far into the past as 1955 was for the original movie, and 2015 marked “the future” for the series. But despite the jokes, one could argue that in fact we are living in the future. At least as far as astronomy and astrophysics goes, we’ve come a long, long way in the past 30 years.
Elementary
In the early 1900s the general view of stars was that they contained about the same ratio of elements as Earth. That is, they were made largely of things like iron, silicon, oxygen and the like, and not much in the way of hydrogen and helium. That’s in direct contradiction with what we know today, but it was a reasonable assumption at the time.
Newtonmas
It’s often said that Isaac Newton was born on December 25, 1642. That’s true in the fact that Newton’s birth is indicated as that date in historical records, but it is more accurate to note that Newton was born on January 4, 1643. That’s is birthday in our modern Gregorian calendar. At the time of Newton’s birth, England used the older Julian calendar, hence the difference in dates.
The Last Astrologer
On this day in 1546, Tycho Brahe was born. Like countless sky-watchers before him, Tycho was an astrologer. He was born in a world before telescopes, where the stars were thought to be fixed an eternal, making their daily motion (along with the Sun, Moon and planets) about a divinely fixed Earth.
Capture the Stars
Although stars have been catalogued by their apparent brightness for centuries, cataloging stars by their color didn’t begin until the early 1900s. Much of this is due to the fact that when we look at stars with the naked eye, most of them appear white. There are a few that appear reddish, such as Betelgeuse, and some that appear slightly blue, such as Regulus. Although stars do vary in color, our eyes aren’t sensitive enough to distinguish it.
Clockwork Twin
The Antikythera mechanism is a strange astronomical calculator. It was discovered in a shipwreck off the Greek island of Antikythera in 1900, and is astoundingly complex. It was a bronze clockwork device with at least 30 gears, and looks like something from the 1400s. But recent research indicates that it likely dates earlier than 200 B.C.
Act of Frustration
Imagine you’re an astronomer interested in comets. You scan the sky with a small telescope, looking for a faint fuzzy patch in the sky. Soon enough you find one. But as you watch it over the next few nights you notice it isn’t moving against the background stars. So it’s not a comet, but rather a nebula. Looking through the …
Wonder Falls
There’s a new video from Human Universe where Brian Cox shows how, in a vacuum, a bowling ball and feathers fall at the same rate. The idea that all objects fall at the same rate regardless of their mass is often attributed to Galileo. It’s commonly said that Galileo proved this fact to be true by dropping masses off the leaning tower of Pisa. But in fact it’s quite likely that Galileo never performed the experiment. Given the experimental apparatus at the time, it’s unlikely that such an experiment would be conclusive anyway. So why was Galileo convinced that objects fall at the same rate?