As astronomers discovered that we live in a great big universe, they considered a fundamental question: is the universe the same everywhere? Imagine if gravity was stronger billions of light years away… Or in the past. It sounds like a simple question, but the answer has been tricky to unravel.

We did a wildly popular three part series about the center, size and shape of the Universe. But every good trilogy needs a 4th episode. This week we look at age of the Universe. How old is the Universe, and how do we know? And how has this number changed over time as astronomers have gotten better tools and techniques?

This week we find out when stars get torn apart from gravity, how we can see supermassive black holes, how liquid water could have existed on Mars in the past, and much more. If you've got a question for the Astronomy Cast team, please email it in to [email protected] and we'll try to tackle it for a future show. Please include your location and a way to pronounce your name.

As we've mentioned before, the Universe is trying to kill you. And for astronauts, that's truer than ever. One step out into the vacuum of space would be a world of hurt for an unprotected astronaut: the freezing cold temperature, the lack of atmospheric pressure, and the deadly radiation, just to name a few hazards. That's why the smart astronaut always puts on a spacesuit first. Let's take a look at the smallest spaceship around.

With Christmas just around the corner, we thought we'd investigate a mystery that has puzzled historians for hundreds of years. In the bible, the birth of Jesus was announced by a bright star in the sky that led the three wise men to his birthplace. What are some possible astronomical objects that might look like such a bright star in the sky? And were there any unusual events that happened at that time?

This week we find out the difference between an astronomer, an astrophysicist, and a cosmologist, the search for the stars that shared our nebula, hidden objects in Lagrange points, and much more. If you've got a question for the Astronomy Cast team, please email it in to [email protected] and we'll try to tackle it for a future show. Please include your location and a way to pronounce your name.

Space is totally inhospitable. If the freezing temperatures don't get you, the intense radiation will kill you. Or the vacuum, or the lack of breathable atmosphere, or meteoroid impacts. Well… you get the idea. That's why most space exploration is done by hardy robots. They don't need to eat, drink or breathe. They get their energy from the Sun, and they've proven they've got the right stuff to explore every planet and major moon in the Solar System. Let's hear it for the space robots.

This week we find out the distance between Betelgeuse and Bellatrex, how astronomers measure distance between objects, the possibility that an object could mess up the orbit of Earth, and the reason for different sizes of stars.

In the old days, astronomers had to beg for telescope time. They'd put together a proposal, convince observatories to gather data for them, crunch that data and release the results. No telescope, no results. But everything's different now. Fleets of robotic telescopes constantly scan the skies, building up a vast database of raw data about the Universe. Anyone who wants can access the information through the Internet, download what they need to do real science. No telescope necessary. Let's look at the development of sky surveys, and how they're changing how astronomy gets done.

Today, time rules our lives. We live each day with the moments broken up into hours, minutes and seconds. We never seem to have enough time. But can you imagine not being able to tell time at all, where the movements of the Sun and the stars was the only way to know what time it was? Let's learn about the history of time, methods of telling time, and Einstein's historic discovery that time isn't as fixed as we thought it was.