Archives For space

Line 1. Let’s start with ‘typical’ humans. The average human adult male is 1.75 metres tall – that’s 3.83 cubits or 5.74 feet. The average female is 1.62 metres – that’s 5.4 light-nanoseconds or 0.008 furlongs.

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You live on Earth (Sol d, perhaps?). This is an Earth-like planet in a Sun-like star system. The third planet of eight in a rich system, including a least one planet populated entirely by robots (Mars, perhaps?). Earth is 12,742 km in diameter and thus has a circumference of 40,000 km or roughly 25,000 miles. Humans live in a thin layer (~20km) around the surface called the troposphere. If the Earth was a beach ball then all life on Earth exists within just 1mm around the surface.

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Through many years of international effort we have managed to keep a ‘space’ station in orbit – just above this troposphere – 1cm above the beach ball. But not high enough up that it can totally avoid the atmosphere – the ISS has to constantly boost itself back up because of air drag. We have sent just 24 people out into deep space, beyond the Earth’s atmosphere. All of then visited the Moon and the last ones returned in 1972: 42 years ago. They were all men, all white, and all American. We could do it again, we could do it better – but we chose not do so. (Mostly for political reasons IMHO.)

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Those astronauts visited the nearest body in space: the Moon – the second brightest thing in the sky . They were kind enough to return some photos to show us how teeny tiny we are, and how delicate out world really is. The Moon sits about a quarter of a million miles away (384,000 km). You could fit all the Solar System’s other planets in that gap.

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But that doesn’t include the Sun – the brightest thing in the sky. The Sun is truly huge. You can fit the Earth inside the Sun a million times. It has more than enough room for all the planets and then some. The Sun itself sits 93 million miles away – which means that light takes 8 minutes to reach us from the Sun. The Sun could have gone out 7.9 minutes ago and you’d only find out… now. Nope: we’re ok. For now.

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And yet we have flung robots into space and downloaded the images they have recorded. Sometimes we take extremely long-range selfies of a sort. Images of the Earth, of humanity reduced to a pixel or two. Here’s one from Mars, one from Saturn and one from out near the edge of the Solar System – taken by Voyager. These images collectively earn us the moniker ‘pale blue dot’. Out by Pluto, the Sun itself is has dimmed to look like an other stars. From Saturn, we are just a couple of pixels as seen by the Cassini probe:

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And truthfully, the Sun isn’t so special. In fact there are stars which make the Sun look even smaller than the Earth does here. VY Canis Major is staggeringly big – and could encompass the Sun 1,000,000,000 times. That’s a million trillion Earths. Oh and VY Canis Major isn’t even visible to the naked eye because it’s so far away that we can’t detect its photons without aid of telescopes or binoculars.

Which brings us to the Galaxy. The Sun is just one of hundred of billions of stars orbiting around the Milky Way. If the Sun was a blood cell then the Milky Way is the size of Europe. The Milky Way is staggeringly big also staggering diffuse – so much so that if you took two Milky Ways, and hit one with the other, then in all likelihood no two stars would collide. They would pass though each other like smoke.

In fact this will happen. The Andromeda galaxy – which is a lot like the Milky Way – is on a collision course with us. In about 4 billion years it will begin to merge with our galaxy in a spectacular collision. We see these happening elsewhere but the sheer scale of this vision in our own night sky makes me want to get a time machine and jump forward to see it happen. The Earth is unlikely to be affected by this, because of the lack of collisions – however our night sky will be spectacularly altered for hundred of billions of years. Makes you realise how dull it is right now. Just kidding!

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But the Milky Way and Andromeda are just two out of hundred of billions of galaxies in the Universe. Gigantic stellar continents floating in a vast, void of almost nothing. Galaxies themselves form structures, and as we have looked deep into the cosmos we have seen one such structure: the Sloan Great Wall. A thick chain of galaxies, loosely bound to each other by gravity, stretching 1.4 billion light years across the Universe and about 1 billion light years from the Milky Way. It’s 1/60 of the Universe across. And yet there are even bigger thing out there.

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The largest known structure in the Universe is the Hercules–Corona Borealis Great Wall. At 10 billion light years across, this huge filament of galaxies in 1/10 the size of the observable Universe. It’s 100,000 time the size of the Milky Way, and 70 million trillion times bigger than than the Sun. We don’t have a good picture of it, but we know it’s there. It’s 7,000,000,000,000,000,000,000 times bigger than the Earth, which is very much bigger than you. I refer you to line 1.

I got into a conversation recently about how some astronomical photos can totally change your whole perspective of yourself and your place in the Universe. There’s several images that come to mind right away – here are my own favourites:

1. The Milky Way (from a very dark location)

Milky Way

Seeing the night sky from a dark site is something most people don’t do very often, now that most of us live in cities. The vision of the Milky Way overhead can be startling, and a pair of binoculars make it more so; revealing that its delicate structure is made of millions of stars. This long-exposure photo of the dust lanes in our galaxy [1] is our first image that can really change your perspective on yourself and your place in the cosmos.

2. Earthshine on a crescent moon

Young Crescent Moon with Earthshine

When the Moon is just a thin crescent in the evening sky you can often see the rest of its face, dimly lit, and slightly reddened. This part of the Moon is not being illuminated by the Sun, like the crescent shape itself, but rather by the reflection of light from the Earth where the Sun has not yet gone down over the horizon. You’re seeing other people’s daylight, bounced back at you from around the world [2][3].

3. Aurora and lightning from the ISS

Sometimes a change in perspective can be quite literal – as with this video of the Earth seen from the International Space Station. The green structures are aurora- the Northern Lights over Canada in this case. You can also catch the occasional flash of lightning. This time-lapse is haunting and shows you a view you could probably never otherwise see.

4. M31 compared to a full moon

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The Andromeda Galaxy is our nearest neighbouring galaxy and can be seen as a faint fuzzy patch in the Northern Sky. What is amazing though, is to realise that in fact it is quite a large object – bigger than our own Moon in our sky. Out eyes just don’t see it very well! Long-exposure images show just how big it really is. Combine this with the fact that it is 200 million light years away [4] and you begin to realise that the galaxy next door is truly enormous. It’s about the same shape, size, and type as our own Milky Way too. So we will look pretty similar to anyone looking up at the sky from a planet in the Andromeda galaxy.

5. Earth from Saturn (and other places)

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There are perhaps no images quite as humbling and shifting as the set of images we would probably call the ‘pale blue dots’. These are the small set of mages of the Earth from far, far away taken by the robots we have sent out into the Solar System. Voyager 1 took one in 1990 from 4.7 billion light years away; Cassini has taken more than one from the Saturnian system (like the one above); a few have been taken from Mars too. All of them show the Earth as just a pixel or so across: encompassing all of humanity, the world, and all life as we know it into a teeny tiny speck against the cosmos.

6. Orion’s Proplyds

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These dark blobs hidden within the star-forming complex of the Orion nebula are known as proplyds – or protoplanetary disks. These are embryonic solar systems in the making. Each of these blobs is far larger than our own Solar System (they get smaller as they evolve into spinning orbits) which gives you some idea as to how large the Orion Nebula is in total. We were once shrouded in such a dusty blob ourselves – though long before the Earth formed.

7. The Sloan Great Wall

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The largest surveys of galaxies reveal a structure in the Universe so vast that is practically beyond comprehension – but let’s try anyway shall we? The Sloan Great Wall is a filament of galaxies, snaking through the Universe that appear to be physically connected to each other – bound by gravity. The ‘wall’ is 1.38 billion light years across. That’s 1/67th of the observable Universe! When light is emitted on one side it doesn’t reach the other end for 1.38 billion years. It is 1,600 times a long as the distance between the Milky Way and Andromeda. I told you it was hard to imagine.

8. Apollo 8 on Christmas Eve 1968

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I thought it would be good to end on something a little closer to home. On December 24th 1968 astronauts Bill Anders, Jim Lovell, and Frank Borman were the voices heard on one of the most-watched television broadcast of all time. As they read passages from the Bible’s Book of Genesis, they broadcast a grainy image of the Earth, as seen from the orbit of the Moon. The world watched themselves from space for the first time, and saw the Earth as a singular marble, set against the deep black of space. The image has since been remastered and still represents an era, and a moment in human history, that many find totally perspective changing. A symbol of a race of beings from a tiny planet, venturing outward to explore space and the worlds beyond their own. Remarkable.


[1] I recently had my first go at some proper astrophotography from a dark site. My target was the Milky Way and the result was this image of the dust lanes of our galaxy toward the centre of the galaxy. I’m pretty happy with it for a first go.

[2] This effect can also be seen on other moons around other planets and is generically called ‘Planetshine‘.

[3] This also serves as a good reminder that there is a part of the Moon we never see – the far side – which is lit by the Sun, but just never seen from Earth.

[4] That distance gets smaller all the time, and Andromeda will actually collide with us in about 4 billion years.

The Real Orbiting Frogs

September 13, 2013 — Leave a comment

Don’t worry I’m not about to start a reality show. You might have seen the picture that’s been circulating of a frog being catapulted from the launchpad of LADEE, the spacecraft is making its way to the Moon now to study dust in the lunar exosphere.

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This amazing image has prompted several people to suggest that perhaps he’s the real ‘orbiting frog’? I’m afraid not.

My blog/twitter name is inspired by a tragicomic 1970 NASA space program called the Orbiting Frog Otolith (OFO). The poor frog who (presumably) lost his life during the LADEE launch had it easy in compared to the OFO bullfrogs that were launched into orbit and later left there to perish whilst sitting in a comical iron-lung-esque device. You can read all about it – and the two frogs – on the OFO Wikipedia page.

I say the LADEE frog ‘presumably’ lost his life. but I suppose we’ll never really know. If he was survived then I think a reality show may be entirely justified.

That’s No Supermoon

June 24, 2013 — 4 Comments

The periodic mention of a ‘supermoon‘ in the news cycle is starting to annoy me. A supermoon is simply not that much bigger than any other Moon!  It’s apparently just perceptible but by no means would you call it ‘super’. Annoyingly though, observation of the so-called supermoon is wrapped up in another effect: the Moon Illusion. This means that people enthusiastically report seeing a really big Moon, but don’t realize that they would likely have thought it big on any other Full Moon night too.

So let me put my rant in some context. The term supermoon was coined by astrologer Richard Nolle about 30 years ago. It refers to a Full Moon or New Moon that occurs when the Moon is in the closest part of its orbit around the Earth. The Moon’s orbit is not perfectly circular and there is a closest point in every cycle (perigee) and a most-distant point too (apogee). At perigee the Moon is closer to the Earth by about 50,000 km (30,000 miles), which is enough to make the Moon appear slightly larger in the night sky. In fact it is about 1.1 times larger in it’s angular diameter on the sky. Expert Moon watchers can see a subtle difference but it’s pretty slight and hardly warrants the title of a ‘super’ moon.

The Moon's motion over one cycle.

The Moon going through one complete orbit as seen from the Earth.

This animated GIF shows a Moon going through one entire orbit (apogee-perigee-apogee) and you can see the changing size (you can also see it undergoing libration, which is the wobbling motion). You can a direct size comparison below. In both these cases you’re seeing it close-up – imaging these things hanging in the sky at a distance. The size change is happening in every cycle, but is most prominent when the Full Moon coincides with perigee, as was the case this week.

Size Comparison for the Moon at Apogee and Perigee

Size Comparison for the Moon at Apogee and Perigee [Source: http://www.fourmilab.ch/earthview/moon_ap_per.html%5D

So there is a difference in the appearance of the Moon but it is very small and you’re unlikely to be seeing this when you go outside to look at a supermoon. What you’re actually experiencing is most likely the Moon Illusion: the optical illusion that the Moon looks larger when it is near the horizon than when it is high in the sky. The Moon Illusion is not well understood but most astronomers are very familiar with it. It may be partially caused by the Ebbinghaus illusion, which is the one that makes the two central circles in the following image appear to be different sizes when they are, of course, the same. When close to the horizon the Moon is compared to objects like rooftops, hills and clouds. When high in the sky is mostly seen in wide-open space. Another explanation may lie in the processes that govern our binocular vision; it might be that the Moon Illusion does not occur of you stand on your head, for example. This has not (yet) been tested widely.

Ebbinghaus Illusion

So what happened over the weekend was that people heard about a supermoon and so went outside to see it. Given that it any observable supermoon is a Full Moon, this means people went out to see it when it was low down in the sky, because Full Moon’s rise late in the evening. Thus they probably experienced the Moon Illusion and reported that indeed the Moon looked very large.

On a final point: the supermoon is also given silly superpowers by some new outlets too. The natural oscillation of the Moon’s distance does indeed affect tides a little, but it does not cause earthquakes, madness or werewolves.