Astronomers Confirm Youngest Supernova Ever Seen

The National Radio Astronomy Observatory reports the youngest supernova seen in the Milky Way. The former star is G1.9+0.3, located about 25,000 light years from Earth. The images below show the expanding remnants of the star over a 23-year period, from 1985 to 2008. From the speed of the expanding gases, astronomers can determine that we’re looking at the system about 140 years after the explosion. (The explosion didn’t occur in 1868, of course.)

Links:

• NRAO Press Release
• Tom’s Astronomy Blog
• Space.com article
• CNN article (Associated Press)
• Wired Science Live Blog of the Announcement

Thinking About Aliens, part 3: How Many Are There?

Note: this is the third and final part in a three-part series.

How many intelligent alien civilizations might exist in the galaxy? We estimate the answer with the Drake equation. This is a somewhat unusual equation. Instead of possessing an unknown quantity for which we might solve, it contains several estimated probabilities, multiplied together to predict the number of intelligent alien civilizations in the Milky Way:

Thinking About Aliens, part 2: What Aliens Might Look Like

Note: This is the second in a three-part series.

The typical alien creature in a science fiction film or television program is best described as a grotesque humanoid. This is likely due to the limitations on the producers, viz., time, money, special effects technology, and imagination. From a cost perspective, it’s easier to dress an actor in a suit than to design and somehow animate a creature whose body bears little resemblance to a human. It’s also much easier to imagine an alien as looking essentially like a human being. And so the great majority of alien creatures in sci-fi productions have a head with sense organs, especially eyes and mouth, in the “right” places, two arms, a torso, and two legs, and possibly a tail. Prominent examples include the peaceful though somewhat mischievous visitors in Close Encounters of the Third Kind (1977), the unnamed, lethal stowaway in Ridley Scott’s original Alien (1979), and the aggressive, well-camouflaged hunter in Predator (1987).

Fun With Orbits, Or How to Slow Down by Speeding Up

Orbits are cool. Let’s see how, shall we?

When a satellite orbits the Earth in a perfect circle, it experiences a centripetal acceleration that depends on its orbital speed v (a constant) and its orbital radius r (also constant):

A centripetal acceleration changes only your direction of motion.  A tangential acceleration changes your speed.  In your car, your steering wheel produces a centripetal acceleration, and your gas and brake pedals produce a tangential acceleration.

The centripetal acceleration experienced by an orbiting satellite is due to the Earth’s gravitational field:

where G is the universal gravitational constant and M is the mass of the Earth. (If you’re going to build a universe, you must decide how strong the force of gravity will be. You do this by setting the value of G. In our universe, and perhaps others, G has the value 6.673 x 10^-11 in SI units.)

50 Years in Space

Today is the 50th anniversary of Sputnik, the first artificial satellite in Earth-orbit, launched by the Soviet Union on 4 October 1957. Sputnik scared the daylights out of the U.S. (so the story goes), and initiated the space race. Twelve years later, two Americans stood on the surface of the Moon–an object never visited by the Russians. This morning, Phil Plait at the Bad Astronomy Blog has a nice article on Sputnik, with some good links.

Easter and the Modern Calendar

We take our calendar for granted, even as we depend on it to plan our lives. Many elements of the calendar seem somewhat arbitrary, such as the division into seven-day weeks and twelve approximately 30-day months. (The latter has its origin in the lunar cycle, which is nearly 30 days long.) But the length of the calendar year is not arbitrary. 365 days is the approximate time needed for the Earth to make a complete orbit of the Sun. This means that from our perspective on the surface of the planet, it takes approximately 365 days for the Sun to return to the same position on the Celestial Sphere.

Ancient Greek Astronomy

One of my astronomy classes this week focused on some of the highpoints of ancient thought about astronomy. It illustrated a fact often forgotten or never contemplated by modern people, that ancient peoples were just as intelligent, curious, and careful in their reasoning as modern thinkers.

10 Things About the Big Bang You Might Not Know

Ten things about the Big Bang you might not know:

1. The Big Bang was not an explosion of matter in the ordinary sense of the term. Explosion entails a previously-existing empty space into which matter is flung in all directions. But the Big Bang theory asserts the creation of space itself. The concept of “location” has no meaning prior to the Big Bang, and we cannot identify a particular location in the universe where the Big Bang occurred. Since the Big Bang is the creation of the universe, the Big Bang occurred everywhere in the universe.