Mon May 11, 2026 GENERAL RELATIVITY DAY
110 years ago, On May 11th, 1916, Albert Einstein's General Theory of Relativity was announced. It supplemented his earlier work on "special relativity", which stated that light travels at the same speed, whether you are moving toward the source of the light, or away from it. With general relativity, Einstein suggested that space itself is curved, the amount of curvature depending on the gravity fields of massive objects like stars and galaxies. Planets don't follow orbits because the sun is pulling on them; rather, they revolve because the sun's mass makes a big dent in the fabric of space-time, and the planets travel like marbles rolling on the inside of a funnel. Our sun’s gravity field is so great that the positions of distant stars are shifted by it. It's all pretty deep.
Tue May 12, 2026 NOVAE AND SUPERNOVAE
For the past couple of years I’ve been going outside every clear evening to look for a nova that is scheduled to appear sometime this year. So far, nothing. A nova is a very hot, dying white dwarf star that is pulling gas off of a nearby companion star. That gas spirals around the white dwarf, and when there’s a lot of it, the gas touches down on the surface of the white dwarf and ignites, creating a flare-up in the star. The white dwarf brightens considerably for a few days, then dims down again – until more gas has piled up around it and the cycle repeats itself. This can go on for years and years. This star, called t Coronae Borealis, flares up every 80 years. It did it in 1866, and again in 1946. If it does flare up again, it will appear as a fairly bright star well to the south of the Big Dipper’s handle. Stay tuned!
Wed May 13, 2026 BERENICE'S HAIR
In the northern sky this evening the faint constellation of Coma Berenices appears to the south of the Big Dipper’s handle. Berenice was the wife of one of the Ptolemies who ruled Egypt. Just before a great battle, Berenice promised to cut off her hair and place it in the temple as a sacrifice if Ptolemy survived. He did, and she did. Then somebody stole the hair – yes - a classic case of hair today and gone tomorrow! This got Ptolemy’s dander up! He ordered his soldiers to comb the palace until they found the hair; some tried to give him the brush-off, but the head priest made up a bald-faced lie: he pointed to this part of the sky and declared that Berenice’s hair had risen up to the heavens to commemorate the occasion. As a result, Berenice's Hair is now a permanent constellation, all because of some great hair-raising battle of long ago.
Thu May 14, 2026 GREAT GALAXY!
In the evening in the summer, or in the fall, or the winter, when the sky is clear and dark, the Milky Way can be seen as a faint band of cloudy light that stretches across the heavens. But in the springtime evening, the Milky Way hugs the horizon in all directions, completely encircling it, and it can be lost in the glow of streetlights. The Milky Way is our home galaxy, and we are inside it. But which is bigger – the Milky Way galaxy or our solar system? Solar systems are billions of miles in diameter, but the disc of our Milky Way is roughly 600 thousand trillion miles across – much bigger, and what’s more, it contains hundreds of billions of solar systems. All of the stars you see up there are part of our Milky Way – great galaxy!
Fri May 15, 2026 ARCTURUS THE INTRUDER
In the eastern sky this evening there is a star that doesn’t belong here – an intruder. It’s Arcturus, the fourth brightest star in our night sky. Most of the stars you see are moving along with our sun, traveling in nearly circular orbits about the hub of our Milky Way galaxy, but Arcturus, an old red giant star, moves at a sharp angle to all the others, plunging along an elliptical path through the disc from up above. Tonight, it’s a mere 37 light years away, that’s a bit more than 200 trillion miles, but in a half million years or so it will have shot down below us, and its ever-increasing distance will make it too dim to see without a telescope. So, enjoy viewing Arcturus while it’s still in the neighborhood!
