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  # 1786562 23-May-2017 11:22
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jpoc:

 

Whatever is doing it, it is at it again:

 

http://www.nzherald.co.nz/technology/news/article.cfm?c_id=5&objectid=11861251

 

The star entered a new dimming phase at the end of last week and the race is on to point some serious telescopes at it.

 

This is important because all we know up to now is that the star's luminosity dips but we have no measurements of how the light spectrum changes during those dips.

 

If we can get that information, we will be a lot closer to working out what is actually going on.

 

 

I love it when "scientists' are trying to solve something they know very little of (just can't get much data from so far away, it's like trying to see if a hangi in Auckland is cooked while sitting in a football stadium in Manchester, without any temperature data other than Auckland airport temperature is rising and falling over 3 hours.

 

All these while they can't even figure out something that they sit on everyday - gravity! Or why planets rotate around their axis!





Involuntary autocorrect in operation on mobile device. Apologies in advance.


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  # 1787836 24-May-2017 23:49
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The current dimming phase seems to be at an end, it lasted around 5 days and saw a maximum dimming of around 3%.Earlier dimming phases had several events, generally starting with smaller ones and getting bigger and then seeing smaller events on the way out. The next few weeks will be very interesting as we can expect full data analysis from the current event as well as perhaps some more dimming events to come.


 
 
 
 


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  # 1787837 24-May-2017 23:52
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joker97:

 

<snip>

 

All these while they can't even figure out something that they sit on everyday - gravity! Or why planets rotate around their axis!

 

 

The rotation of planets is fairly well understood. Our planet formed from a rotating cloud of gas, dust and small rocks. It still has pretty much the same angular momentum as that rotating cloud because angular momentum is conserved.


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  # 1787877 25-May-2017 08:30
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jpoc:

 

joker97:

 

<snip>

 

All these while they can't even figure out something that they sit on everyday - gravity! Or why planets rotate around their axis!

 

 

The rotation of planets is fairly well understood. Our planet formed from a rotating cloud of gas, dust and small rocks. It still has pretty much the same angular momentum as that rotating cloud because angular momentum is conserved.

 

 

Except for Venus which rotates in the opposite direction (and Uranus - which rotates with an axis pointing to the sun)

 

Of course this needs explanation, so the explanation is usually given that this must have been the result of an asteroid impact. Actually AFAIK there's no evidence at all that it was from an asteroid impact, except for the observation that they don't rotate as expected - and there are alternative theories to explain how this might have happened.  

 

 

 

 


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  # 1787881 25-May-2017 08:43
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Hold on, So are you guys saying that they based a game off a 1970 book called Ringworld?
They called it Halo?


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  # 1788454 25-May-2017 23:58
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Fred99:

 

<snip>

 

Except for Venus which rotates in the opposite direction (and Uranus - which rotates with an axis pointing to the sun)

 

Of course this needs explanation, so the explanation is usually given that this must have been the result of an asteroid impact. Actually AFAIK there's no evidence at all that it was from an asteroid impact, except for the observation that they don't rotate as expected - and there are alternative theories to explain how this might have happened.  

 

 

 

I do not think that is correct.

 

In the case of Uranus, an impact (with a protoplanet) is generally considered to be the best explanation and there is evidence for this. Uranus has a thermal anomaly. It radiates a lot less heat than would be expected in comparison to other planets in the solar system. This suggests that its core is colder and this would be accounted for if an exoplanet impact was enough to knock the rotational axis of the planet and also to eject a substantial part of the planet's core.

 

In the case of Venus, there is no need to suggest an impact. The planet has a super-dense atmosphere and most of the insolation that strikes the planet goes to heating the atmosphere and generating extremely strong winds. The atmosphere is orders of magnitude more dense than that of the earth and average winds are around one order of magnitude up on ours. That means that there is enough force exerted on the planet to have a significant effect on its rotation. The combination of wind forces and the tidal effects from the sun are enough to mean that the rotation of Venus varies chaotically over astronomical timescales. One interesting point is of course that we must be able to account for the change in angular momentum as the rotation of Venus speeds up or slows down. There is a transfer of angular momentum between the rotation of the planet about its axis and its orbit around the sun. There will also be a transfer between the planet's atmosphere and the solar wind.


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