Mon July 21, 2025 APOLLO 11 LANDING ANNIVERSARY
On July 20th 1969 at 4:18 pm Eastern Daylight Time, Apollo astronauts Neil Armstrong and Buzz Aldrin, aboard their lunar spacecraft Eagle, touched down on the moon, landing on a basaltic rock lava basin called the Sea of Tranquility. At 10:56 pm, Neil Armstrong stepped onto the lunar surface, followed by Buzz Aldrin about ten minutes later. They were outside for two-and-a-half hours, setting up several lunar science experiments and collecting about fifty pounds of moon rocks. Shortly before 2 pm Eastern Daylight Time on July 21st, they blasted off from the moon and rejoined Command module pilot Mike Collins who was on board the Columbia spacecraft in lunar orbit. All three came back to earth on July 24th fifty-six years ago today. The last time anyone walked on the moon was back in 1972; when will we return?
Tue July 22, 2025 STARS OF THE SUMMER TRIANGLE
The Summer Triangle is made up of three bright stars that are well-placed in the eastern sky after sunset at this time of the year. The highest star, Vega, is the brightest of the three, but the star Altair, below and a little to the south of Vega, is almost as bright. The third star, the northernmost one, is called Deneb, and it’s no match for the brightnesses of the other two. But that’s because, as you may have guessed, Deneb is much farther away from us, so its light is correspondingly dimmer. Altair is a mere seventeen light years away – that’s a little over a hundred trillion miles. Vega is a little farther away, twenty-five light years, but it’s an intrinsically brighter star, and that extra luminosity makes it brighter. But Deneb, which is the dimmest star, is also about a hundred times more distant; if Deneb were as close to us as the other two, it would be bright enough to cast shadows!
Wed July 23, 2025 LOOK-BACK TIME
If you can manage to live for a full century, go outside at night on your 101st birthday and look at the star at the end of the handle of the Big Dipper, in the northwest this evening. The light from that star, Alkaid, left there the day you were born (This calculation comes from data collected by the Hipparcos satellite; some of my colleagues insist that Alkaid is really 104 light years away, so you may want to hang on a few more years just in case.) Now go farther out: in the south is the star Antares, 500 light years away. If it went supernova today, we wouldn’t know about it for another 500 years. It takes light time to travel across the Universe. This phenomenon, Look Back Time, means that the farther something is from us, the older it is. So when we look at the Andromeda Galaxy, 2.5 million light years away, it’s what that galaxy looked like 2 and a half million years ago. What does it look like now? Not sure, but I’ll know, in about 2 and a half million years!
Thu July 24, 2025 SUMMERTIME MILKY WAY
In the summertime, when the skies are clear and dark, it's possible to see a galaxy on display. This galaxy is called the Milky Way, and it is our home, a giant star city, one of hundreds of billions in the vast emptiness of the universe. The Milky Way is shaped like a spiral disc or pinwheel, some hundred thousand light years or so across. One light year equals six trillion miles, which means our galaxy is over six hundred thousand trillion miles in diameter - big! There are perhaps two hundred billion stars in the Milky Way, and our sun is but one solitary star about two-thirds of the way out from galactic center. Go out tonight and look for the arm of the Milky Way - a faint hazy band of light arching across the sky. In the late evening, around 10 PM, it stretches from due south – the constellations Scorpius and Sagittarius - toward the zenith – the three stars of the summer triangle, and then down to the constellation Cassiopeia in the north.
Fri July 25, 2025 THE MILKY WAY AND THE LOCAL GROUP
The Milky Way, part of it at least, can be seen tonight under clear dark skies. It spreads across the eastern sky, from Cassiopeia in the north to Sagittarius in the south. The Milky Way is our home galaxy; we live on a planet orbiting a star about two-thirds of the way out from its center. We have satellite galaxies, most notably the Large and Small Magellanic Clouds. And there’s a bigger spiral galaxy about 2 and a half million light years away: its catalog number is M31, but we know it best as the Andromeda Galaxy. Now besides the Milky Way and M31, there are about 30 other, smaller galaxies in the immediate neighborhood (and by “immediate neighborhood,” we mean anything that’s within a million parsecs of here.) This cluster of galaxies is called the Local Group. Most of them are fairly small and contain only a billion or so stars. M31 and the Milky Way are the Group’s gravitational “anchors”.
