Date: November 28, 2009

Title: An Armchair Tour of the Universe in 10 Minutes

Podcaster: Rob Bowman

Organization: None

Description: The universe is simply vast. It’s enormous in ways our brains cannot fully comprehend. Despite this, we also have the sort of brains that need to at least try to make sense of the scale of things if we hope to understand them. In this short podcast we will be taking a tour of the entire universe, so hold on to your hats! Along the way, we’ll see moons, planets, stars, galaxies, vast clouds of interstellar dust and distant beacons. We’ll see the very ancient history of the universe and we’ll mention some of the ways that we actually know how far away things are. It’s a breathless ride, so let’s get started right away…

Bio: Rob Bowman is an electronics/software engineer by day and an armchair astronomer by night. He lives under the orange glow of city skies, so contents himself with downloading and manipulating images from the world’s great telescopes, reading and listening to any astronomy media he can get his hands on, and wondering if 43 is too old to become a professional astronomer.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by Joseph Brimacombe.

Transcript:

Hi this is Rob Bowman for 365 days of astronomy.

The universe is simply vast. It’s enormous in ways our brains cannot fully comprehend. Despite this, we also have the sort of brains that need to at least try to make sense of the scale of things if we hope to understand them. In this short podcast we will be taking a tour of the entire universe, so hold on to your hats! Along the way, we’ll see moons, planets, stars, galaxies, vast clouds of interstellar dust and distant beacons. We’ll see the very ancient history of the universe and we’ll mention some of the ways that we actually know how far away things are. It’s a breathless ride, so let’s get started right away …

Here on earth, we have a certain distance scale that we’re used to. We think it’s a long way across the Atlantic, say from London to New York. It’s about five and a half thousand km, or eight hours in a jet plane. Our brains have evolved to understand slow journeys of tens or hundreds of km, not thousands, so that seems a long way, but compared to the distance scales of the observable universe, it is microscopic.

On July 16th 1969, the Apollo 11 mission launched from the Kennedy Space Centre in Florida, and reached the moon about three days later, having travelled over 385,000 km. One of the many things the crew achieved whilst on the surface, was to place a special kind of mirror called a retro reflector. To this day we are bouncing a laser off this mirror and timing the round trip of the reflected light, so we know how far away the moon is to great accuracy. The Apache point observatory in New Mexico can do this experiment and get a moon distance accurate to a few millimetres.

So the moon’s quite a long way away. Well, we’ll see about that. Let’s take a trip to the Sun using the Apollo craft. Pack plenty of food, because it’s going to take us about 4 years. The sun is about 150 million kilometres away on average, and we call this distance an Astronomical Unit, or AU for short. Maybe we could invent a craft that could travel at the speed of light, then get in it and zip to the Sun instantly. Not even then. Light takes a full 8 minutes to get from the Sun to earth. Some solar flares can spew out huge gobs of hot plasma at very high speeds, but thankfully they still take hours or days to get here, giving us just enough time to turn off our satellites to minimise the risk of them being fried.

OK, so it’s a long way to the Sun. Well, not really. Our solar system as a whole is much, much bigger. Pluto, the lonely outer planet, or dwarf planet if you prefer, orbits the Sun forty times further away in a distant region known as the Kuiper belt. The Voyager 1 space probe, launched in 1977, is the fastest ship ever built by Humankind. It is currently travelling at a whopping 62,000 kilometres per hour, and yet it took about 10 years to pass the orbit of Pluto. Voyager 1 is currently about 110 astronomical units away. The edge of the Solar System is often considered to be the heliopause – a theoretical boundary where the Sun’s solar wind is stopped by the interstellar medium; where the solar wind’s strength is no longer great enough to push back the stellar winds of the surrounding stars. We don’t really know how far away the heliopause lies, but Voyager is probably there or thereabouts. So, we have sent a spacecraft to the outer reaches of our Solar System.

Excellent news indeed – next stop the stars? Well, no – not really. It’s true to say that our solar system is gigantic, because it is many orders of magnitude larger than anything of human scale. On the other hand, the solar system is a mere speck in our galaxy. Our sun’s nearest stellar neighbour, Proxima Centauri, is a red dwarf star in the southern constellation of Centaurus. It is absolutely in our back yard, being only thirty-nine trillion, nine hundred billion kilometres away. That’s about 268,136 astronomical units. OK, we definitely need some help with our units here, because the numbers are getting out of hand. If you’re a hardcore astronomer, you’ll probably want me to start talking about Parsecs at this juncture, but, at the risk of disappointing all you space junkies, I’m going to use light years because I think they’re more intuitive in this context. We’ve already met light minutes – remember it takes light about 8 minutes to travel from the sun to the earth. Well, a light year is simply the distance travelled by light in one year. Proxima Centauri is about 4 light years away. In cosmic terms it is bang slap next to us – think of it being your neighbours house, with all the planets and junk in between as the lawns, hedges and driveways. And yet it IS very distant. Any craft we could build would take several hundred or perhaps a few thousand years to reach it. Even radio signals have a round trip time of eight and a half years, making communication with the neighbours a bit tricky. As for going to parties there, forget it.

When we find, sorry I mean IF we find intelligent life around Proxima Centauri, we will have to control our excitement, tempering it with patience almost beyond human endurance. Talking to our neighbours is going to be a long drawn out affair. Imagine sending them a radio transmission, which propagates across space at the speed of light, perhaps just a simple “Hello” to start with. We’d have to wait over eight years for a reply!

So, we can now just about emotionally understand the distance to our nearest stellar neighbour – but what about our galaxy? How big is it? Well, it’s about one hundred thousand light years across its disk. It’s not actually a very big galaxy, though. The nearest spiral galaxy similar to our own is the Andromeda Galaxy which lies about 2.5 million light years away. Take a piece of paper and draw a pretty little spiral galaxy about a centimetre across to represent our galaxy – Andromeda would be 25 metres away. That’s a lot of empty space between galaxies, and yet Andromeda is part of what we consider to be our local group of galaxies.

We can continue travelling through the universe in our minds, and as we do so, the objects we encounter are vast and truly very distant from each other. It’s not called space for nothing – most of it is just a very hard vacuum. Travel now two hundred thousand light years to the Tarantula Nebula, then realise it’s still five hundred light years to the other side of the gigantic glowing gas cloud.

Some of the most distant observable objects in the universe are known as quasi-stellar objects, or quasars. They are galaxies that have at their core a supermassive and unimaginably dense object such as a black hole. As gas and dust and stars spiral into the rotating core at a significant fraction of light speed, very very bright beams of energy are flung outwards because of these motions and also the core’s very powerful magnetic field. Some quasars are trillions of times brighter than our sun. You wouldn’t want to live near one, but their extreme luminosity means we can see them even though they are billions of light years away. Because they are so very far away, we can use them as reference points – they don’t appear to move in the sky by parallax as we change our position in space whilst orbiting the sun. We use these fixed points to measure the parallax motion of closer stars, which means that using some simple geometry we have measured the distance of about a million stars within a range of about ???????? We Humans just love making maps.

I really hope that this podcast has helped with your own understanding of the enormity of our universe. I can sort of understand these scales and distances on a gut feel level, and they never cease to amaze me.

End of podcast:

365 Days of Astronomy
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The 365 Days of Astronomy Podcast is produced by the New Media Working Group of the International Year of Astronomy 2009. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.