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Host: Fraser Cain
Guests: Thad Szabo, Scott Lewis, Ian O'Neill, Alan Boyle, Nancy Atkinson, David Dickinson, Jason Major, Matthew Francis, Nicole Gugliucci

LINKS:
(Check out the comments for some more excellent discussion!)
+Alan Boyle on Virgin Galactic: http://www.nbcnews.com/science/nbc-ai...
+Nancy Atkinson on the hybrid solar eclipse: http://www.universetoday.com/106045/h...
+Jason Major on baby supermassive black holes http://www.universetoday.com/106187/e...
+Ian O'Neill on quasars (BLACK HOLES DON'T SUCK) http://news.discovery.com/space/astro...
+Alan Boyle on Chelyabinsk http://www.nbcnews.com/science/russia...
Security cam of Chelyabinsk: http://www.universetoday.com/106226/n...
+Matthew Francis on LUX: http://arstechnica.com/science/2013/1...
+Nancy Atkinson on the sun (not literally) http://www.universetoday.com/106278/s...
+Scott Lewis on Frontier Fields: http://www.knowthecosmos.com/astronom...
+Matthew Francis on Earth-density exoplanet: http://arstechnica.com/science/2013/1...
+David Dickinson on GOCE: http://o.canada.com/technology/space/...
Kepler Orrery: http://www.universetoday.com/106168/h...
Fireball FAQs: http://www.amsmeteors.org/fireballs/f...

We enjoy the light from the Sun during the day, and then the comforting glow of the Moon at night.

But the light coming from the Moon is an illusion.

As you know, you're actually seeing the reflected light from the Sun, bouncing off the Moon which acts like a mirror.

A really terrible mirror.

When astronauts walked on the surface, they reported that it was dark grey, the color of pavement.

Because of its dark color and bumpy surface, it only reflects about 12% of the light that hits it.

Additionally, the amount of light we get from the Moon depends on the point of its orbit.

During its first and last quarters, the Moon is half illuminated, but it's only 8% as bright when it's full.

Just imagine the surface when its only partly illuminated.

With the Sun at a steep angle, the mountains cast long shadows.

This makes the lunar surface much darker than when it's directly illuminated.

During the full Moon, it's so bright that it obscures fainter objects in the night sky.

Many astronomers put their telescopes away during this phase, and wait for it to go away.

When the Moon is highly illuminated, it reflects so much light we can even see it during the day.

The brightness of the daytime sky completely washes out the light from the stars, but the Moon is even brighter, and so we can can see it in the sky during the day.

The Moon follows an elliptical orbit around the Earth, changing its distance and brightness quite a bit.

When it is at its closest point, and it's full, this is known as a supermoon.

This Moon can be 20% brighter than normal.

You've probably experienced how the Moon can cast shadows. In fact, there are three objects in the sky that can cast shadows.

The Sun, of course, the Moon... and Venus.

Venus is the next brightest object in the sky, after the Moon. It reflects 65% of the sunlight that hits it.

Every few months, Venus reaches its brightest time - that's when you can see your shadow.

On a night with no Moon, head far away from city lights.

Let your eyes adjust and watch as your hand casts a shadow on a white piece of paper, illuminated only by Venus.

One last thought on reflected light.

We talked about how bad a mirror the Moon is, reflecting only 12% of the light that hits it. That's nothing.

Saturn's moon Enceladus, on the other hand, reflects about 99% of the light that falls on it. If astronauts ever get the chance to walk on the surface of Enceladus, it'll feel like freshly fallen snow.

Dr. Thad Szabo is a professor of physics and astronomy at Cerritos College. He's also a regular contributor to many of our projects, like the Virtual Star Party and the Weekly Space Hangout. Thad has an encyclopedic knowledge of all things space, so we got him to explain a few fascinating concepts.
In this video, Thad explains the strange mystery of dark energy, and the even stranger idea of the Big Rip.

If we look at the expansion of the universe, at first it was thought that, as things are expanding while objects have mass, the mass is going to be attracted to other mass, and that should slow the expansion. Then, in the late 1990's, you have the supernova surveys that are looking deeper into space than we've ever looked before, and measuring distances accurately to greater distances than we've ever seen before. Something really surprising came out, and that was what we'll now use "dark energy" now to explain, and that is that the acceleration is not actually slowing down - it's not even stopped. It's actually getting faster, and if you look at the most distant objects, they're actually moving away from us and the acceleration is increasing the acceleration of expansion. This is actually a huge result.

One of the ideas of trying to explain it is to use the "cosmological constant," which is something that Einstein actually introduced to his field equations to try to keep the universe the same size. He didn't like the idea of a universe changing, so he just kind of cooked up this term and threw it into the equations to say, alright, well if it isn't supposed to expand or contract, if I make this little mathematical adjustment, it stays the same size.

Hubble comes along about ten years later, and is observing galaxies and measuring their red shifts and their distances, and says wait a minute - no the universe is expanding. And actually we should really credit that to Georges Lemaître, who was able to interpret Hubble's data to come up with the idea of what we now call the Big Bang.

So, the expansion's happening - wait, it's getting faster. And now the attempt is to try to understand how dark energy works. Right now, most of the evidence points to this idea that the expansion will continue in the space between galaxies. That the forces of gravity, and especially magnetism and the strong nuclear force that holds protons and neutrons together in the center of an atom, would be strong enough that dark energy is never going to be able to pull those objects apart.

However, there's a possibility that it doesn't work like that. There's actually a little bit of experimental evidence right now that, although it's not well-established, that there's a little bit of a bias with certain experiments that dark energy may get stronger over time. And, if it does so, the distances won't matter - that any object will be pulled apart. So first, you will see all galaxies recede from each other, as space starts to grow bigger and bigger, faster and faster. Then the galaxies will start to be pulled apart. Then star systems, then planets from their stars, then stars themselves, and then other objects that would typically be held together by the much stronger forces, the electromagnetic force objects held by that will be pulled apart, and then eventually, nuclei in atoms.

So if dark energy behaves so that it gets stronger and stronger over time, it will eventually overcome everything, and you'll have a universe with nothing left. That's the 'Big Rip' - if dark energy gets stronger and stronger over time, it will eventually overcome any forces of attraction, and then everything is torn apart.