Archive for category Astronomy
A bit of shameless scaremongering
The media loves to grab onto any new technology or experiment that has even the tiniest whiff of controversy about it and whip up some fanciful scare stories about how it will (not if, will) end the world and we all have to sign a petition and protest. Fair enough, with big experiments there is always going to be a small risk involved. The potential benefits to science and progress always far outweigh the potential risks, however, as if they didn’t the experiment just wouldn’t be feasible.
A recent example is the LHC. Everyone got into a huge panic shortly before the first beam last September when the idea came to light that a micro black hole might be formed. People immediately hear the words ‘black hole’ and ‘new experiment’ and ‘expensive’ and immediately assume a group of geurilla scientists are trying to take over the world. These people should not be allowed to leave the house.
The purpose of this post is not to address these trivial issues though. It is infact to address a much more serious and much more likely issue. That a nearby supernova will wipe out all life on Earth.
A supernova is what happens when a massive star begins to collapse under its own gravity, then, not being able to take the immense pressures and forces involved, suddenly begins rapid nuclear fusion and catastrophically explodes, expelling a vast amount of energy and leaving behind a neutron star or black hole.
One of the most famous supernovae is SN1987A, which is the first supernova to occur in 1987. It was highly luminous and even visible to the naked eye for a while. But even then, 1987A was a distant supernova.
A supernova closer to home, say, within a kiloparsec, has a high chance of ending a lot of life.
Some calculations:
Assumptions:
1. The stars in the Milky Way are spherically distributed.
2. The mass of the Milky Way is entirely composed of stellar objects.
3. All stars in the Milky Way are roughly as massive as the Sun.
Taking these assumptions into consideration, we will most likely come out with an underestimate of the stellar number density of the Milky Way, purely based on assumption number 1.
Mass of the Milky Way: ~ 6×10^11 Solar Masses (1.42×10^42 kg)
Radius of the Milky Way: ~ 50,000 Light Years (4.7×10^20 m)
Average Density of the Milky Way: ~ 3.2×10^-21 kg/m^3
Now assumption number 4, the stars are uniformly distributed throughout the Milky Way.
Density within a radius of 1kpc: ~4×10^38 kg
Stars within a radius of 1kpc (using assumptions 2 and 3): ~200,000,000
So if we make an underestimate that 1% of the stars in the Milky Way are large enough to produce enough energy in a supernova to kill us all, that makes close to 2 million high mass stars that are close enough to wipe out all life on Earth.
In fact, it’s been proposed that the reason for one of the mass extinctions in the Earth’s history was caused by a nearby supernova.
The reason we aren’t all kicking up a fuss about it? Well, for one, there’s absolutely nothing we can do about it. There’s no way to predict when a supernova will happen (aside from observe the stars for evidence of their evolutionary stage) and there’s definately no way to stop one. The second reason is that a supernova is a relatively rare event. The Milky Way has around 100 billion stars. The average rate of supernovae in our galaxy is around 5 per century. So the probability of a single star in the Milky Way going supernova is around 3×10^-14. This means that we can expect a nearby (within 1kpc) star to go supernova around once every 1,000,000 years.
A mass extinction caused by a nearby supernova has, literally, a one in a million chance of happening.
Stargazing
One of my favourite things to do on a clear night is stargaze. It is one of the most common aspects of our lives, yet never fails to be fascinating.
On any given night, given a good clear sky and a location free of too much light pollution, one can easily find the band of the Milky Way, stretching all the way across the sky, our neighbour galaxy Andromeda (or M31), various meteorites, Saturn, Jupiter, Mars, Venus (only around dusk/dawn), and of course the Moon. Occasionally it is even possible to see Mercury, although its postion as nearest planet to the Sun makes it only visible close to Sunrise/Sunset, and succeptible to being drowned out by the light of the Sun.
Observing the planets requires a favourable position in both our and the planets orbit, but a lot of the time at least one planet is visible.
Taking this fascination with the night sky further, one can observe with a telescope (or a good pair of binoculars). This then allows an observer to see even more objects, various star clusters and nebulae are faintly visible, but definately there.
The best thing to do if you get the chance to stargaze with an instrument is to study the Moon. The Lunar surface is riddled with impact craters and vast mountain ranges, many of which are clearly visible, even with a small pair of binoculars. Just scanning over the Lunar surface can make hours of fascinating observation time.
More distant than the moon, the planets offer another fantastic observation opportunity. Venus waxes and wanes as it goes along its orbit, the rings of Saturn are distinguishable, and even the four moons of Jupiter, Galileo’s very own observation, are visible.
Another thing which immensely fascinates me is Astrophotography. For this to be done best, it requires a good digital SLR camera with a long exposure on a nice clear night. I, however, lack this equipment, so am forced into taking pictures of the Moon. Still, some very good pictures can still be taken, showing the detail on the surface of the Moon.
Here’s a picture I took of the Moon with my telescope and a standard digital camera.
For better pictures, head over to Astronomy Picture of the Day.
Ah, the Perseids
It’s that time of year again. The Perseids reach their peak and everyone goes meteor shower crazy.
I will admit, spotting a meteorite just as it ‘flashes’ is a pretty spectacular event and it never gets old. I was just hanging out of my bedroom window trying to spot a few myself.
Reaching a peak at around 22:20pm (on the 12th August) and then again at around 3:20am, with just over 1 meteor per minute, it’s pretty easy to find a few just by staring at the constellation Perseus.
I find it pretty fascinating where they come from.
Everyone has heard of comets, right?
Well, comets orbit the Sun, and in their wake they leave a trail of ice and rock. As Earth continues on its own orbit, it intercepts some of these trails at certain points of the year. The meteorite trails you see in the sky are formed when the icy part of the trail melts and the rocks burn up as they enter the atmosphere.
Now, the Perseids shower originates from the debris from the comet Swift-Tuttle. Not a very well known comet, but nevertheless it has a funny name…
A more famous comet associated with a popular meteor shower is Halley’s comet. This gives rise to the Orionid meteor shower, so called because the meteors radiate from the constellation Orion. This shower occurs around mid October, and is a bit dimmer than the Perseid shower, but is so much cooler because it’s Halley’s comet.
Even better than that, however, are the Taurids.
Caused by a lesser known comet, comet Encke, they also produce a relatively dim shower. However it occurs close to Hallowe’en, which earns it some cool points. The debris stream of the comet has also been disrupted by the gravity of larger planets, like Jupiter, into two distinct streams, which can be seen as the Northern Taurids and Southern Taurids.
Even bettter than that, though, is the possible claim the Taurids can make.
They may be the cause of the Star of Bethlehem.
Now, a quick disclaimer. This doesn’t have to assume that the Christian religion is correct, or that a ‘God’ even exists. Just that Jesus Christ was born around the time we all know…
With that out of the way, the Taurids have a periodicity. This means that it has a peak in activity roughly every 3000 years. Astronomers have estimated that the next peak in activity will occur around 3000AD. Which makes the previous peak around 0AD. Jesus’ Birthday.
This is a kind of nice thought, and it has Astronomical credability, although a more likely scenario would be the triple conjunction of Jupiter and Saturn that also occured at that time. That event can also be placed at that time with a bit more accuracy.
The conjunction of two planets means that they ‘overlap’ each other on the sky. Now, they may not exactly overlap, and the light from the planets will add together to make a particularly bright point of light. If this happened around that time, it would have definately seemed like a ‘divine message’, it’s not everyday that you see a bright light appear in the sky three times in a row…
But then, this is all moot as we then have to assume that three ‘wise’ men would follow a strange bright star on a whim and that it would lead them to a newborn child in a barn…
Make of the mythology what you will, but the astronomy stands up 
A Space Odyssey
Posted by Tom in Astronomy, Science, Technology on July 28th, 2009
It’s been 40 years since the Apollo missions and the first manned lunar landings and I, for one, have been watching the TV programmes quite a bit. It’s all the same old knowledge though, filled with things everyone already knew. The crew of Apollo 11 underestimating their position and having to land in precarious circumstances, the cancellations of the later Apollo missions due to lack of political will, the more recent US revival in space exploration by ‘Dubya’ and his directing NASA to get a man on Mars in the next few decades.
What I found more interesting was the missions planned by other nations. Particularly China.
OK, so many people know that China have a lunar exploration programme. Many people know that China plan to land men on the moon around 2020/30.
What I didn’t know was that following their manned missions, China will begin construction of a permanently occupied lunar base!
If this did happen, it would completely change space exploration. I’m thinking along the lines of 2001 here. Minus the evil computer.
Whoever decided to build an extremely powerful artificial intelligence and give it a BRIGHT RED EYE anyway?!
A lunar base would not only be exceedingly cool, but would offer a ‘recharge station’ for spacecraft going from Earth to more distant destinations, not needing anything like the huge rockets required to take a craft to the escape velocity of Earth. Taking off from the Moon would be a much easier task.
Hopefully once it’s all completed the Chinese will share their lunar base with the other nations, perhaps there’ll even be an Earth-wide space exploration programme and all of the political agendas involved in space exploration will be gone. Maybe I’m wishing there though.
None of this is fully OFFICIAL yet, but the renewed interest in space exploration is definately a good sign of things to come!
Further reading:
Solstice
So today, 21st June, marks the summer solstice. The longest day of the year and the midpoint of summer.
If you were to mark out the position of the sun on the sky at midday every day for a year, the summer solstice is the day when the Sun is at its highest point in the sky. Conversely, the winter solstice (21st December) is the day when the Sun is at the lowest point of the year at midday. This naturally leads to the solstices being the longest and shortest days (or shortest/longest nights) of the year, as in summer, the sun has longer to travel on the sky from sunrise to sunset, and shorter in winter.
The reason we have the solstices is for the same reason we have seasons, the Earth is tilted on its axis. In the summer, in whatever hemisphere you are in, the Earth is tilted towards the Sun, in the winter, it is tilted away from the Sun. The summer solstice marks the point in the Earth’s orbit when the axis is most tilted towards the Sun, and when it is the summer solstice in the northern hemisphere, it’s the winter solstice in the southern hemisphere.
Now, you probably already know about the summer and winter solstices, but not everyone has heard of the vernal or autumnal equinoxes (around March 21st and September 22nd), . These are analagous to the solstices, in that they mark the midpoint of spring and autumn (or fall) respectively. However, the equinoxes mark the time when day and night are of the same length, which corresponds to the perpendicular points on the Earth’s orbit to the solstices.
The equinoxes are formally recognised when the position of the Sun on the sky crosses the Celestial Equator, which is the projection on the sky of the Earth’s equator.
With a bit of simple stellar geometry it is quite simple to prove all of this stuff, but I’ll not bother here.
I’m sure someone out there finds this stuff interesting!
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