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Archive for the ‘Astronomy’ Category

Or The Space Game, by ESA.

The Space Game Screenshot

Minimize delta vee by moving the planets around (this changes the probe's arrival time at the planet). This shows my best solution so far, with some playing one evening, about 13 km/s

This is a nice javascript webpage where a probe is shot from Earth to Jupiter with gravity assists at Venus (twice), Earth and Mars. You try to achieve the lowest propulsive delta vee. You decide when the spacecraft arrives at each encounter and the program basically calculates the rest. It’s quite a nifty little piece of Javascript, the future of web applications is like this. It works fine with Chrome on Linux at least. Probably IE will have problems but who uses that anyway?

I’m ranked at #39 at 12.74 km/s… Far behind the gurus who get below 10 km/s readings! There are apparently some prizes for the top three, but I think people are in it for the fun of it.

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Tim Lambert exposes another one of Tim Blair’s articles. How can Blair be one of Australia’s top bloggers (in terms of traffic)? Just read some comments at Blair’s – they’re horrible excercises in outrage based on completely false information. The article ultimately linked to that’s supposed to be the source of all this knowledge doesn’t support their points – it opposes them diametrically.

The sun has always been recognized a factor in Earth’s climate, but it is only a minor factor in recent 20-30 year changes. It is factored in the climate models that are shown in the IPCC reports. This article that supposedly started this furor continues in the exactly same line.

And then these people are voting, based on this information they get from the media, like Blair. This can not result in anything but regression.

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“On the internet, everybody is an expert.” “Knowledge seems to correlate inversely with confidence.” And many other one-liners proven true in a godawful blogpost. Jennifer Marohasy has been a policy advisor for the Australian government, a prominent think tank member and an invited person to talk at many places. And here she attempts to refute the greenhouse effect altogether, and manages to violate conservation of energy at the same time (due to the confusion about energy versus power, see explanation below). It’s sad that people lacking basic high school level physics knowledge post something like this and others flock to defend it. It is just plain wrong. There is no opinion in these matters of physics, the model either describes nature well or it utterly fails.

If these are the people that set the policies in the western world, the decline has already started. I wonder if the internet has actually sped up this, or will it help prevent it? Are the experts always outnumbered by the lay people? Or would most people have the education (or logic capability and the time to quickly learn) to understand that what is peddled here is completely wrong?

Ultimately, when you get deeper into any complex issue, be it science or diplomacy, it becomes impossible for the average person to understand completely what is going on, and they have to trust others on what to do, how to expend the resources. But of course, the question becomes, who to trust. This is where peer review and open science should make it trustworthy. Spreading incorrect physics does not further public policy. You can’t get the right decisions out, if the data that goes in, is wrong.

The Greenhouse Effect Explained

In an equilibrium, an object receives an energy flow, and the energy also flows out at the same rate, otherwise it would be accumulating somewhere. This is the case with Earth. Energy is measured in Joules while power is Joules per second which also has the short hand Watts.

Now, Earth is in a vacuum so energy can flow in and flow out only via radiation. Also, objects that have more energy, that is, hotter objects, radiate more of their energy per second (the radiation power is dependent on the fourth power of temperature).

So, if the power going in is increased (like the sun getting brighter), then, initially, more energy is flowing in to Earth than flowing out, and Earth starts getting hotter (accumulating energy). The temperature increases and Earth starts radiating more and more, until it reaches an equilibrium where it radiates out as much as it gets in from the sun. Then the energy flows are in balance. So the result of cranking up the sun for Earth was an equilibrium state where there is more radiation in, more radiation out and more energy on Earth.

In the greenhouse effect, energy flows in normally but the energy flow coming out is limited slightly by some factor. Because the inflow is greater than the outflow, this starts accumulating energy on the object. Again the temperature (energy level) rises and the object radiates more and more, until it radiates exactly the amount that it is getting in from the sun. Then it is in equilibrium again and doesn’t heat up anymore.

There are lots of possible analogies. Water level can be thought of as energy, and water flow as energy flow or power. Then, a bucket with lots of holes can reach an equilibrium, where the amount poured in per second is the same that comes out of the holes. You can increase the water level either by increasing the rate you pour in (crank up the sun), or blocking some of the holes (the greenhouse effect).

Also, a clear night is usually much colder than a cloudy one. That is because when the sky is clear, the warm Earth can radiate it’s energy straight into space, while when there are clouds, the warmth stays in.

Designing spacecrafts, the concepts of power, energy, heat and radiation are very important too. In the vacuum of space, computer processors produce some heat that is hard to carry away (on Earth the heat is put into ambient air which is carried away by cooling fans, but there’s no air in space). They heat and heat until they simply radiate the heat away. But if there are some spacecraft walls, they might reflect the heat back. Hence there are radiators onboard spacecraft, where you pump coolant fluid from warm stuff inside to the outside where the heat radiates into space. If you have a nuclear reactor in space, the power system requires a temperature difference. The reactor is hot and the radiator is cool. If the flow to the radiator is cut, the reactor gets hotter (there is nowhere for the energy flow to go) and hotter until it melts and breaks. Then it probably goes subcritical, and the energy flow is cut. The heat radiates from the glowing droplets that are left behind.

And of course the last analogy is sleeping with a blanket. Your body produces some heat and that heat’s flow out is hindered by the blanket, hence you stay warmer. The blanket does not produce any energy and actually the blanket stays colder than your body at all times. Also, you can’t heat up a cold passive object by just wrapping it in blanket. The power (energy rate) produced by the body is constant and hence in an equilibrium the power flow out must be the same. A blanket lets through more energy when the temperature difference is larger. Hence your body temperature (energy level) grows until the heat flowing out is the same as what your body produces. You can get too hot easily with a thick blanket.

So, on Earth, how is it possible to only limit outgoing energy but not limit the incoming at the same time? This is because the energy comes in from the sun as mostly visible light, but the warm earth radiates in infrared. The greenhouse gases block only infrared light, hence blocking outflow but not intflow.

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Nowadays new exoplanets are found every week. Exoplanet blog systemic has an article from February about possible Earth-like planets around Alpha Centauri B.

What’s remarkable is the easiness with which they could be detected if some resources are spent. And if a planet like that exist, it’s one of the top destinations for future interstellar probes and eventually human craft, because of the short four light year distance.

I’ve always found exoplanets very fascinating. They represent truly new knowledge that wasn’t yet available to us only a few years ago. If the graph below is to believe, the trend is promising, and in only a few years we might have even publicly notable results about Earth-like planets.

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Our solar system is only marginally stable, and also “filled to the brim” with planets. If you added another planet, the system would eject planets until it reached stability. During the disk accretion and the planetary embryo collisions, small variations determined the characteristics of the system, for example how many rocky planets would result from the chaotic process. A lot of stuff was ejected from the system into interstellar space.

So, with nature’s tendency to “fill all the slots”, expect many earth-like planets to be found in the habitable zones of stars in the future, when detection methods advance sufficiently. Currently, they only favor big planets close to small stars.

There is an excellent medium length article on this from the astrobiology magazine (found initially spacedaily’s blog) that was written in September 2007.

Classic Drake Musings

When looking at the history of Earth , half of the time there has been only single cell life. And only the latter half of the existence of Earth has been with an oxygen rich atmosphere. (Public domain picture from Wikipedia.)

History Of Life On Earth, Linear Time

Here is a good page summarizing life very well too at California Space Institute.

Thus the current rapid change and development phase with humans is extraordinary. It is hard to imagine what the next 100 million years will be like, as humans have only existed a few million years. Will we go extinct and will another species dig our remains and wonder why it all was destroyed? Do we have some fundamental flaws that will be our doom? Or will a random natural disaster destroy us? There are some tests of time ahead for humanity, that is certain.

And if there are lots of other Earth-like planets in this galaxy, what is their history like? As a first cut, if there are 100 billion stars in the galaxy. A large portion of them are sun-like stars and a large portion of them have earth-like planets. For example, this recent article at Centauri Dreams says how many young sun-like stars harbor warm dust at earth-distance or AU, a sign that they will develop rocky planets there later – and the older stars don’t have dust anymore, possibly indicating that the planets have formed. The rocky planet harboring number could be twenty to sixty percent of F5 to K3 spectral type stars.

So there could be thousands or even millions of civilizations on the milky way. And perhaps half of them could be millions of years older than ours.

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In the end of January, a 100 m class asteroid called 2007 TU24 will pass near earth, somewhat beyond moon’s distance. It’s not visible with the naked eye, but only with reasonable size amateur telescopes.  JPL has more.

This was only detected  in November 2007. If some other big one was headed towards earth one day, it’s possible there wouldn’t be much time for warning…

Here is a nice calculator to estimate the impact effects. The energy equivalent of a 200 m low velocity asteroid is about 100 megatons TNT or twice the biggest hydrogen bomb ever. At 100 km distance, a loud bang would be heard.

The best and most cost effective way to currently work with the asteroid threat is extensive sky surveys, which are already being carried out. Later, something more is required.

Of course, humanity has many other threats facing its comfort (an asteroid wiping out humanity to extinction is a nonexistent threat) and if those are more probable, they need to command more attention than asteroids.

That is, if rational resource allocation is used.

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I can link you some nice images:

A good thank-you to the people who produce this stuff for the benefit of all to the internet. This whole phenomenon was only starting at large about ten years ago. Information availability is so much better nowadays than in the past, and it is a marvellous thing.

Also a more personal thanks to all the commenters, linkers and readers during the fall!

Sergei Pavlovich I can be somewhat busy here, although not as busy as Sergei Pavlovich seen here, but I’ll try eventually posting all the things I’ve promised in the past. 🙂

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