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Your favourite Solar System facts

Zapp Brannigan said:
Think of it a bit like temperature. All human experience is in the realm of a bit cold to a bit hot, so you'd think there's no limit to how cold something can be - whatever the record cold is, just go a bit colder. But that's not the case, there is a physical constraint placed on the property of temperature, namely absolute zero where all molecular activity comes to a standstill. There is no such thing as -1K.

Time is similar. However far back you go, you'd think can always go 1 second earlier. Except you can't, because there is a physical constraint on time (namely the existence of this universe) which means there is a time zero*. There is no such thing as before time zero.

*This is a simplified version which assumes time as linear. Not strictly true, but for practical purposes let's go with it.
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No. I get the concept of absolute zero and how it can’t physically be achieved and that. But I can’t accept that there was nothing and from that nothing a singularity erupted in to the universe, which then expanded and continues to expand, in to nothing, not empty space, but nothing. Strikes me as an explanation that works to allow other stuff to be worked on, but doesn’t really satisfy the answer to the question of what the nothing was where the singularity exploded in to and to where it continues to expand in to.
 
Bahnhof Strasse said:
No. I get the concept of absolute zero and how it can’t physically be achieved and that. But I can’t accept that there was nothing and from that nothing a singularity erupted in to the universe, which then expanded and continues to expand, in to nothing, not empty space, but nothing. Strikes me as an explanation that works to allow other stuff to be worked on, but doesn’t really satisfy the answer to the question of what the nothing was where the singularity exploded in to and to where it continues to expand in to.
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As soon as anyone say the universe started as a singularity and us expanding, there's an obvious parallel with a balloon being blown up. The difficulty is that the balloon is only expanding in 3 dimensions, whereas the universe itself is expanding in at least 4 dimensions* which makes it almost impossible to visualise. It means that the universe is finite in size but has no boundary edge, unlike the balloon which has its surface. Having no boundary edge means it's not expanding into anything, or even expanding into nothing - there is no outside, it's simply becoming a bigger version of itself.

Travel at the speed of light for an incredibly long time and you would end up back where you started in 3 dimensions, except it wouldn't be where you started because of the 4th dimension (time) and you would be outside the expected timescale for the existence of the universe.

*IIRC 11 is quoted by Stephen Hawking? I could be mis-remembering.
 
It's not quite in our solar system but I'm intrigued by the so far inexplicable KIC 8462852, aka the WTF Star or Tabby's Star. Some say it might be a megastructure built by aliens. It's probably not, but for the moment it's billed as the most mysterious star in the universe. Tabby explains:
 
Bahnhof Strasse said:
Ah, you’ve been taken in by that old chancer. He was OK in the Simpsons, but the rest of it was made up as he went along.
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Tbf I'm trying to remember from A Brief History of Time and the Quest for the Theory of Everything, but he was merely reporting the accepted thinking of the time. It wasn't his own research that led to that conclusion.

But yeah, his biggest achievement was the Simpsons :D
 
Helps to imagine time not as a linear, 1 dimensional measurement but as 2 dimensions ("real" time + "imaginary" time at right angles to it).

If you take longitude/latitude as such an example, you can plot this on the surface of a sphere (globe) and you'll see it's possible to circumnavigate back to the same "spot"
 
Apparently, despite not being the furthest planet from the sun, Uranus is the coldest. How is that possible?
 
Nylock said:
Apparently, despite not being the furthest planet from the sun, Uranus is the coldest. How is that possible?
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Total guess, but imagine it's similar to why Venus, not Mercury, is the hottest - temperature is determined by climate/surface conditions, as well as distance from the Sun.

For example, in the case of hottest planet: Mercury has no (little) atmosphere, so doesn't retain the heat, whereas Venus has a dense atmosphere and so retains a lot of heat and is therefore 'hotter' than Mercury. I believe it's referred to as "the hell planet" or similar :D
 
Lord Camomile said:
Total guess, but imagine it's similar to why Venus, not Mercury, is the hottest - temperature is determined by climate/surface conditions, as well as distance from the Sun.
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Yes, they're measuring the temperature of the top of the atmosphere, so heat-trapping gases and the amount of convection will affect that. It's also thought to have lost more of its internal heat early on in a collision that knocked it onto its side.

Why is Uranus the coldest planet in the Solar System? | BBC Sky at Night Magazine

A big mystery about Uranus is its lack of heat. Uranus is the coldest planet in the Solar System, temperatures in its cloud tops averaging –224°C.
www.skyatnightmagazine.com
 
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