In a few hours, many of us will get to see a rare total eclipse of the Sun. Total eclipses are rare because a very tight alignment of the Sun, the Moon, and the Earth are necessary. Even then, the alignment is so precise, the shadow of the Moon only cross a small stripe across the planet. As the “Great American Eclipse,” this is very well branded. We have driven to just outside Knoxville, from Maryland, where we will get about a minute and half of totality, during which night will fall. On the drive, the kids and I talked a lot about the event, and they thought these three facts were really cool.
The Moon is Getting Farther Away
The Moon’s gravity is responsible for the ocean’s tides. The tide goes in and the tide goes out, and it is very easy to explain. But the tidal forces are slowly wearing down the Earth, through a process called tidal friction. The result is that the Earth is slowing its rotation, making the day just a touch longer. This is why we get a leap second every couple of years.
But, if you recall from basic physics, we have to conserve energy. If energy is lost somewhere, it will get picked up somewhere else. And the Moon gets it! It makes the Moon go just a little bit faster in its orbit, as it spins around the Earth. Going just a little bit faster means it gets pushed out just a touch. The result is 4 centimeters per year, or about an inch and a half.
The Sun is Younger on the Inside
Einstein developed the laws of relativity, and things get weird here. One of the cooler things that happens with relativity is that gravity can seriously distort both space and time. The Sun, which isn’t that big as stars go, is still pretty massive and things with greater mass have greater gravity. And that means space and time are warped.
A few years back, three Danish physicists thought about this and using some basic math, figured out how much of a difference it makes. It means not only is the Sun younger on the inside, it is 39,000 years younger on the inside than the outside. But this isn’t an excuse for not losing weight. You can also watch this cool video about it here:
Speaking of the Sun, Light is Old
We probably all learned as kids that light takes just about 8 minutes and 20 seconds to get from the Sun to the Earth. But what we didn’t realize is this is from the surface. Light, or the energy that the light reveals, comes from the core of the Sun, where fusion takes place.
Light is sometimes a wave and sometimes a particle. Those particles, called photons, carry the actual energy of light. The photons originate in the core and they bounce around inside the Sun. They travel at 299,792,458 meters per second, which is quite a speed. But they bounce around inside the sun. It turns out, all that bouncing around and traversing layers of the Sun takes some time. It can be from 10,000 years to 170,000 years for a photon to get from the core to the surface. After it leaves the surface, it goes at full speed toward the Earth!