What is a supernova?

There are actually two kinds of supernova (pl. supernovae). The one referred to as a Type II supernova is generally the one people think of when they hear the word “supernova.”

During the “life” of a star, the pressure created by nuclear fusion exerts an outward force that is balanced by the inward force of gravity. When the star runs out of fuel, the pressure is gone and the inward force of gravity causes the star to collapse. As the star collapses it releases gravitational energy that heats and ejects the outer layers of the star. It’s these exploding outer layers that can briefly out shine the entire Galaxy and create what we see as a supernova.

What makes our sky the colour blue?

This may seem somewhat of an optical illusion. Our Earth’s atmosphere is made up of mostly nitrogen molecules. And, it is these molecules that scatter blue light when sunlight passes through them, which makes the sky appear blue.

You’ve probably noticed that when you look at mountains at a distance, they appear blue in colour. And, the more distant the mountains, the more blue they appear to be. This is because you are looking at them through more nitrogen molecules.

Here’s another interesting tidbit. It is because we see the sky as blue, that we are tricked into seeing our Sun as the colour yellow. Can we always believe what we see? Stay tuned to find out the true colour of our Sun.

How big is our Galaxy?

Just how big is our Galaxy? Let’s put this into perspective by using the speed of light. Our Sun is 150,000,000 km away and at that distance it takes light about eight-and-a-half minutes to reach the Earth. Although we can use this as a measure of distance, it is a bit awkward and a little too small to use. Stars are much, much farther away. So, astronomers use the distance light travels in one year, which is about 9.5 trillion km. The disc of our Galaxy is 100,000 light-years in diameter and the halo of globular clusters is 200,000 light-years in diameter. Think about that; it takes light, the fastest thing in the universe, 100,000 years to travel across the disc of our Galaxy. That adds up to 9,500,000,000,000,000,000 km! Can you imagine?

How long does it take to get to the moon?

The answer to that question is a bit like it would be on Earth; it depends on how fast you travel. One of the problems with space travel is that you can’t just step on the brakes to stop. You have to fire your engines in the opposite direction and this uses a lot of fuel. So, the Apollo missions needed enough speed to escape the Earth’s gravity but not too much speed or they would have had to carry a lot of braking fuel to get into a lunar orbit in order to land. The Astronauts ended up taking three days to get to the moon, which probably didn’t make them happy. Image being stuck in a vehicle a bit smaller than a Volkswagen bug with two other people for three days! Fortunately, the trip home was faster.

How old is the universe?

So, how many birthdays has the universe had? We all know how old we are. Someone, who was around when we were born, told us on what date we were born and then we count forward from that time. The problem is no one was around when the universe was born so we can’t use that method.

We can figure out how old stars are and assume the oldest stars in the universe must still be younger than the universe itself. Since the universe is expanding we could "run the clock backwards" and arrive at an age for the universe. As the universe expands it also cools down. With this in mind, we could measure the temperature of this Cosmic Background Radiation and arrive at an age.

Do stars really twinkle?
 
Why do stars twinkle? Well, they don’t always twinkle. The reason they twinkle, or sometimes don’t, is because of the Earth’s atmosphere.

There are small pockets of air that have different temperatures and these small pockets bend light from the stars in different directions. If the direction is away from our eyes the star seems to disappear. And, if the direction is towards our eyes the stars reappears. This creates the twinkling effect.

What does this mean? The more turbulent our atmosphere is the more the stars twinkle, which is why on a warm, windless summer night that you can look straight up and the stars appear very steady and even feel a little bit closer.

Why is the planet Mars red?

Everyone has heard Mars described as the red planet, but where does that red colour come from? To put it simply, Mars is covered in iron oxide dust — known by its more common name rust that is red.

Now, where did the rust come from if there’s no water on Mars? Originally, the rust was considered to be evidence that there was once water on Mars and it was during this period that the rust had formed. The discovery of hematite, which is a type of iron oxide that forms in the presence of water, supports the idea of a wet past for Mars.

The planet’s thin atmosphere is still strong enough to whip up powerful dust storms that scour the rust from the rocks and send tiny flakes high into the atmosphere to be deposited all over the planet. And, that’s how we see Mars as the red planet.