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Hosts: Fraser Cain, Scott Lewis

Astronomers: Bill McLaughlin, David Dickinson, Tom Nathe, Mike Phillips

Viewing: M103, Cocoon Nebula, Comet Lovejoy, more to come!

The Earth orbits the Sun in the Solar System, and the Solar System is embedded within a vast galaxy of stars.

Just one in hundreds of billions of galaxies in the Universe.

Ours is called the Milky Way because the disk of the galaxy runs across the sky as a band of glowing light, like spilled milk.

Astronomers had suspected the Milky Way was made up of stars, but it wasn't proven until 1610, when Galileo Galilei turned his rudimentary telescope towards the heavens and resolved individual stars in the band across the sky.

With the help of telescopes, astronomers realized that there were many many more stars in the sky, and all of the stars that we can see are a part of the Milky Way.

If you could travel outside the galaxy and look down on it from above, you'd see that the Milky Way is a barred spiral galaxy measuring about 120,000 light-years across and about 1,000 light-years thick.

For the longest time, the Milky Way was thought to have 4 spiral arms, but newer surveys have determined that it actually seems to just have 2 spiral arms: they are called Scutum--Centaurus and Carina--Sagittarius.

It's very difficult to figure out what the Milky Way looks like exactly, because we're embedded inside it. If you'd never been out of your house, you wouldn't know what it looked like from outside. But you'd get a sense by looking at other houses in your neighborhood.

Our Sun is located in the Orion Arm, a region of space in between the two major arms of the Milky Way.

The spiral arms are formed from density waves that orbit around the Milky Way. As these density waves move through an area, they compress the gas and dust, leading to a period of active star formation for the region.

Astronomers estimate that there are between 100 and 400 billion stars in the Milky Way, and think that each star has at least one planet. So there are likely hundreds of billions of planets in the Milky Way, and at least 17 billion of those are the size and mass of the Earth.

Our Sun is located about 27,000 light years from the galactic core. At the heart of the Milky Way is a supermassive black hole, just like all of the other galaxies.

This monster is more than 4 million times the mass of the Sun.

Our Sun takes about 240 million years to orbit the Milky Way once.

Just imagine, the last time the Sun was at this region of the galaxy, dinosaurs roamed the Earth, and the Sun has only made 18-20 trips around in its entire life.

The Milky Way, like all galaxies, is surrounded by a vast halo of dark matter. Nobody knows what it is, but its mass helps keep the galaxy from tearing itself apart as it rotates.

It's believed that our galaxy formed through the collisions of smaller galaxies, early in the Universe. These mergers are still going on, and the Milky Way is expected to collide with Andromeda in 3-4 billion years. The two galaxies will combine to form a giant elliptical galaxy, and their supermassive black holes might even merge.

The Milky Way and Andromeda are part of a larger collection of galaxies known as the Local Group. And these are contained within an even larger region called the Virgo Supercluster.

You might be amazed to know that dung beetles actually navigate at night using the Milky Way.

If you've never seen the Milky Way with your own eyes, you should take the chance when you can. Go to a place with nice dark skies, free from light pollution.

Look up and appreciate the Milky Way, and wave hello to all the neighboring stars who share our galaxy with us.

Virgin Galactic CEO George Whitesides

Previously, I've talked about how quickly the Earth is rotating, and I've talked about why it's spinning.

But what would happen if the Earth suddenly stopped rotating?

Keep in mind, this is totally impossible.

Still, I find topics like this super interesting to think about.

If the Earth actually stopped rotating instantly, it would be very *very* bad for everything on the surface of the planet.

Consider this. If you're standing on the equator, you're traveling at 465 meters/second from West to East.

If the Earth put on the brakes, your momentum would keep you flying at the same speed until *friction* slowed you down.

Imagine the jumbled forests, oceans, buildings and unfortunate animals after that event - it would be carnage.

The atmosphere is also turning at 465 meters/second with us. If everything suddenly stopped, it would be like a simultaneous hurricane of epic proportions on almost every part of the planet.

The closer you get to the poles, however, the less damage it would cause.

If you were standing on the North Pole, you'd hardly feel it.

Let's imagine the Earth slowed down more gradually, taking a few days to come to a halt that didn't tear the landscape into fine mist of dirt, seawater and a variety of organic material.

The stars would hang fixed in the sky; only the planets would move around, continuing their paths around the Sun.

A day on Earth would now last 365 days. In other words, it would take a full year for Earth to fully orbit the Sun, bringing it back to the same location in the sky. Each year would include one long day, and then one long night. You can imagine how that would be devastating to plants and animals.

We get a hint of this at the poles, where you can experience weeks of permanent night and then weeks of permanent day. But imagine 6 months of night, followed by 6 months of day.

The planet's tilt gives us our seasons. As we define the Earth's tilt as its rotation in relation to the Sun. A stationary planet would effectively have no tilt at all.

Without that tilt, there'd be no axis, and no seasons. Although we would still have North and South poles.

Because of its rotation, turning once every day, the Earth is actually a flattened ball, or if you prefer, an oblate spheroid.

Without that rotation the Earth would become a perfect sphere. This sounds interesting and probably harmless, but it's actually a *big* problem.

Because of the Earth's bulge in the middle, the oceans are held out at the equator by 8 km. On perfect sphere Earth, the world's oceans would redistribute, flooding many regions of the planet with an immense volume of water.

We'd end up with a single continent around the middle of the planet, with oceans surrounding the north and south poles.

Let's assume that if the Earth stopped turning, the Earth's core would stop rotating within it as well.

This natural dynamo generates the magnetic field that surrounds our planet and protects life from radiation from space.

Whatever life still alive would be irradiated from the Sun and cosmic rays if it didn't live underground.

So, if the Earth suddenly stopped turning, it would be very bad, even catastrophically bad.

Fortunately, it's completely impossible for this to happen.

Sometimes the Sun is quiet, and other times the Sun gets downright unruly. During the peak of its 11-year cycle, the surface of the Sun is littered with darker sunspots. And its from these sunspots that the Sun generates massive solar flares, which can spew radiation and material in our direction. What causes these flares, and how worried should we be about them in our modern age of fragile technology?

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We record Astronomy Cast as a live Google+ Hangout on Air every Monday at 12:00 pm Pacific / 3:00 pm Eastern. You can watch here on Universe Today or from the Astronomy Cast Google+ page

Welcome to the Universe Today YouTube channel.

Learn about space and astronomy from our various videos.

Guide to Space: Short explainer videos from Fraser Cain investigating various concepts in space and astronomy.

Astronomy Cast - A weekly fact-based journey through the cosmos with Universe Today publisher Fraser Cain and Dr. Pamela Gay, a professor at the University of Southern Illinois, Edwardsville.

Weekly Space Hangout - A weekly roundup of the big space and astronomy news stories of the week with a team of space and astronomy journalists. Hosted by Fraser Cain.

Virtual Star Party - Join Fraser Cain, Scott Lewis and a team of astronomers for a live view of the night sky. We'll broadcast whatever's up in the sky with whatever telescopes aren't rained out. See the Sun, Moon, planets and deep sky objects, live on your screen.

The number of protons defines an element, but the number of neutrons can vary. We call these different flavors of an element isotopes, and use these isotopes to solve some challenging mysteries in physics and astronomy. Some isotopes occur naturally, and others need to be made in nuclear reactors and particle accelerators.

Some astronomers are control freaks. It's not enough to buy a telescope, they want to craft every part of the experience with their own hands. If you're ready, and willing to get your hands dirty (and covered in glass dust), you can join thousands of amateur telescope makers and build your own telescope from scratch.

The Universe is filled with hot fusion, in the cores of stars. And scientists have even been able to replicate this stellar process in expensive experiments. But wouldn't it be amazing if you could produce energy from fusion without all that equipment, and high temperatures and pressures? Pons and Fleischmann announced exactly that back in 1989, but things didn't quite turn out as planned...