|
Science and Astronomy Questions
|
|
| Huesudo | Date: Saturday, 08.10.2016, 08:59 | Message # 811 |
|
Observer
Group: Users
Spain
Messages: 11
Status: Offline
| Quote PlutonianEmpire (  ) or the answer that Alf Cen cant have Gas giants like Avatar
I'm curious about that. Is there a post explaining the reason?
|
| |
| |
| JackDole | Date: Saturday, 08.10.2016, 09:35 | Message # 812 |
 Star Engineer
Group: Local Moderators
Germany
Messages: 1742
Status: Offline
| Quote PlutonianEmpire ( ) that Astrology is bogus?
I did not know this was scientifically proven!
I do not believe in astrology.
But that stars have an influence on my life, I do not consider it to be more improbable than the quantum entanglement.
Quote PlutonianEmpire ( ) that Alf Cen cant have Gas giants like Avatar
Why can Alpha Centauri not have gas giants? (Of course there can be no Unobtanium. Therefore, it is called Unobtanium. If there was an element with the properties, it would not be a Unobtanium.)
The speed of light is, of course, a problem.
I have only understood it (to some extent) when I realized that the speed of light is not the highest speed attainable in the universe, but that it is the only speed that exists in the Universe!
Everything that exists in the universe moves with the speed of light through space-time.
A photon, which moves with the speed of light through the three spatial dimensions, stands still on the time axis.
There is no 'time' for the photon.
For objects like us, which move only minimally in the spatial dimensions, goes almost every movement into the time.
This means that we are moving at almost the speed of light on the time axis.
And the faster we move in space, for example with a space ship, the slower we move in time.
If we were able to fly with the speed of light, time would stand still. If we were able to fly to Alpha Centauri like a photon, about 4.5 years would pass in the outer world. For us, there would be no time at all because we were standing still on the time axis.
But the real speed with which we move is always the speed of light.
( For me, it's perfectly fine if people are a little skeptical about the things that are told by scientists (the village elders, the shamans, the wise man of the tribe, whatever).
Otherwise we would still stare at the mountains on the horizon, and think that is the edge of the world that can not be overcome.)
Don't forget to look here.
Edited by JackDole - Saturday, 08.10.2016, 11:10 |
| |
| |
| apenpaap | Date: Saturday, 08.10.2016, 09:51 | Message # 813 |
 World Builder
Group: Users
Antarctica
Messages: 1063
Status: Offline
| Quote JackDole ( ) I did not know this was scientifically proven!
I do not believe in astrology.
But that stars have an influence on my life, I do not consider it to be more improbable than the quantum entanglement.
Well, it's practically impossible to prove a negative, so technically it's not scientifically proven that astrology is bogus. However, we can test its predictions and find that they don't come true more often than random chance indicates. Put another way, you can take any horoscope, switch around the predictions between signs, and you'll find people still report the prophecies mostly came true, even though they're now getting prophecies for the wrong sign.
Quote Quote PlutonianEmpire ()
that Alf Cen cant have Gas giants like Avatar
Why can Alpha Centauri not have gas giants? (Of course there can be no Unobtanium. Therefore, it is called Unobtanium. If there was an element with the properties, it would not be a Unobtanium.)
Alpha Centauri can't have gas giants because we would have found them by now. Since Alpha Centauri is so nearby, we can place an upper limit on the mass of any undiscovered planets that could still be there just by the limits of our current methods. I'm not sure exactly where this limit lies, but it's below gas giant level.
I occasionally stream at http://www.twitch.tv/magistermystax. Sometimes SE, sometimes other games.
|
| |
| |
| JackDole | Date: Saturday, 08.10.2016, 11:06 | Message # 814 |
|
Star Engineer
Group: Local Moderators
Germany
Messages: 1742
Status: Offline
| Quote apenpaap ( ) Put another way, you can take any horoscope, switch around the predictions between signs, and you'll find people still report the prophecies mostly came true, even though they're now getting prophecies for the wrong sign.
This proves only that so far no one has succeeded in making exact predictions.
Or rather, if someone has made any exact predictions, he has kept them to himself, and they are not generally known.
But it does not prove that astrology is nonsense.
Although I personally think astrology is nonsense. But even I myself have occasionally been wrong. 
Quote apenpaap ( ) Alpha Centauri can't have gas giants because we would have found them by now.
Okay, I did not think of it. I think I can accept that.
However, I must confess that I am generally somewhat skeptical about our ability to discover exoplanets.
It is the talk of measured values which are so enormously small that, statistically speaking, they are almost not true.
But of course I can not really judge this. 
Don't forget to look here.
|
| |
| |
| steeljaw354 | Date: Saturday, 08.10.2016, 11:38 | Message # 815 |
 World Builder
Group: Users
Pirate
Messages: 862
Status: Offline
| Watsisname, I mean if that moon would stay in the orbit our current moon is in and rotate once every 6 days, like the earth was never hit by the mars size object and captured this moon into the orbit we have currently.
|
| |
| |
| Huesudo | Date: Saturday, 08.10.2016, 13:21 | Message # 816 |
|
Observer
Group: Users
Spain
Messages: 11
Status: Offline
| Quote apenpaap ( ) Alpha Centauri can't have gas giants because we would have found them by now.
Oh, I thought you meant that something impeded A Cen from having gas giants
|
| |
| |
| PlutonianEmpire | Date: Saturday, 08.10.2016, 18:49 | Message # 817 |
 Pioneer
Group: Users
United States
Messages: 475
Status: Offline
| Yeah, the current upper mass limit for worlds orbiting Alf Cen is approximately 10 Earth masses, based on RV measurements. 
Specs: Dell Inspiron 5547 (Laptop); 8 gigabytes of RAM; Processor: Intel® Core™ i5-4210U CPU @ 1.70GHz (4 CPUs), ~2.4GHz; Operating System: Windows 7 Home Premium 64-bit; Graphics: Intel® HD Graphics 4400 (That's all there is :( )
|
| |
| |
| Watsisname | Date: Saturday, 08.10.2016, 22:57 | Message # 818 |
 Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| Quote JackDole ( ) It is the talk of measured values which are so enormously small that, statistically speaking, they are almost not true.
Well, the the charge of the electron is 0.0000000000000000001602 Coulombs, but we can measure it and know it's true. It's mass is 0.0000000000000000000000000000009109 kilograms, but we can measure it and know it's true.
Measurement of small numbers is not in itself a problem at all. The problem is precision. To distinguish any number from zero, your measurement must be of sufficient precision such that the number itself is significant. A quantity might even be huge -- say 100 kilometers. But if your ability to measure distance is only precise to 1000km, then 100km is indistinguishable from zero.
If a planet causes its star to wobble by only 1 meter per second, then to discover it you must be precise to tenths of a meter per second. Which we can do! Similar idea for transit method. We must be able to measure changes in the brightness of the star to hundredths, thousandths, or even ten thousandths. Which we can do. Then, further confidence that this measurement is real -- that it really is a planet -- comes from repeated observation. A real planet must consistently produce the same result with each orbit.
Quote steeljaw354 ( ) Watsisname, I mean if that moon would stay in the orbit our current moon is in and rotate once every 6 days, like the earth was never hit by the mars size object and captured this moon into the orbit we have currently.
Oh, I completely missed your second post -- sorry! Ok, so first off, it's pretty hard to know what Earth's rotation rate would be in this scenario.
Earth's current rotation rate slows down due to the tidal interaction. The rate of change of the rotation rate is proportional to the square of the Moon's mass (some really neat astrophysics behind this), so the 62% more massive moon would slow Earth's rotation rate about 2.6 times faster. Instead of losing about 1.7 milliseconds per century, we'd be losing 4.4 milliseconds per century.
However, this rate of change isn't constant and depends very sensitively on how far away the moon is. Since the real moon was formed from the impact and was originally much closer to Earth, there's a complex history of change in Earth's rotation rate. And the moon-forming impact itself surely changed Earth's rotation as well, which would not happen in this captured-moon scenario. So we can't really say what the length of day on Earth would be now -- we can only say how quickly it is changing.
What would the moon look like? It would be 62% bigger, and 2.6 times brighter when full. It would be a bit more impressive of a presence in the sky, but not a whole lot. Correction: it's 62% more massive, not 62% larger. It's actually smaller -- 79% the size of our Moon. It is 38% fainter when full. Less impressive in the sky, but it makes bigger tides. Neat.
It would be interesting if it has a 6 day rotation rate. People, or whatever other intelligent life exists in this world, would not only see different phases of the moon but also different faces.
Tidal evolution would also affect the moon's 6-day rotation rate. Using the formula for tidal locking timescale:
The moon would become tidally locked pretty quickly -- only about 10 million years.
|
| |
| |
| steeljaw354 | Date: Sunday, 09.10.2016, 00:32 | Message # 819 |
|
World Builder
Group: Users
Pirate
Messages: 862
Status: Offline
| Watsisname, Why would it be smaller? Can you make this in Space Engine?
Edited by steeljaw354 - Sunday, 09.10.2016, 00:45 |
| |
| |
| Watsisname | Date: Sunday, 09.10.2016, 02:15 | Message # 820 |
|
Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| I was going by the properties of the moon you showed, which is smaller and denser. It doesn't have to be that way. If you are looking at a scenario where Theia, instead of impacting the Earth to form the Moon, settles into orbit to become a moon itself, then that moon would be much larger and more massive -- something like 10% of Earth's mass and half the diameter of Earth. It would raise larger tides, be bigger on the sky and provide more light. It would still become tidally locked very quickly. But the exact numbers depend on exactly what Theia was, and this varies across different models.
This can be made in Space Engine. See the tutorial for how to make a planet.
|
| |
| |
| steeljaw354 | Date: Sunday, 09.10.2016, 02:42 | Message # 821 |
|
World Builder
Group: Users
Pirate
Messages: 862
Status: Offline
| Watsisname, I just made it. The Barycenter and orbital period is probably dead wrong. What would it be like to have Theia as a moon?
Edited by steeljaw354 - Sunday, 09.10.2016, 02:42 |
| |
| |
| Watsisname | Date: Sunday, 09.10.2016, 07:23 | Message # 822 |
|
Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| The tides would be big: five or six times larger than the tidal change now.
The moon would be about 75% larger on the sky and provide three times as much light, assuming the same albedo.
The barycenter would be well outside the Earth: about 21,400 miles from the center and 17,500 miles above the surface.
|
| |
| |
| steeljaw354 | Date: Sunday, 09.10.2016, 14:43 | Message # 823 |
|
World Builder
Group: Users
Pirate
Messages: 862
Status: Offline
| Watsisname, Would Earth and Theia tidally lock to eachother like Pluto and Charon?
|
| |
| |
| Watsisname | Date: Sunday, 09.10.2016, 22:05 | Message # 824 |
|
Galaxy Architect
Group: Global Moderators
United States
Messages: 2613
Status: Offline
| Yes, and fairly quickly (on geologic timescales). If we set them at the current Earth-moon distance and let them both start with a rotation period of 12 hours, then Theia would become tidally locked in a few million years, and Earth would become locked in a few hundred million years.
|
| |
| |
| steeljaw354 | Date: Sunday, 09.10.2016, 22:28 | Message # 825 |
|
World Builder
Group: Users
Pirate
Messages: 862
Status: Offline
| Watsisname, Interesting! Could life possibly form on both worlds? Would Theia stay in it's current orbit or will it move out or in?
|
| |
| |
ENG
New site
Spain 
Germany 
Antarctica 
Pirate 
United States 
