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Math problem

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- Fri, 26 Sep 2014 14:29:27 EST vUNowU0Q No.54441
File: 1411756167954.png -(17766B / 17.35KB, 640x558) Thumbnail displayed, click image for full size. Math problem
Anyone want to help me out with this problem? I'm new to astronomy/physics and I haven't the faintest.
8 posts omitted. Click View Thread to read.
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Paul Goldsmith - Fri, 24 Jul 2015 21:11:43 EST euFuFwSC No.55558 Reply
>>54441

> A mass is dropped directly on top of a half circle. As it rolls of the side...

Top lel
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Edwin Salpeter - Mon, 31 Aug 2015 01:06:20 EST OMGzRHpD No.55646 Reply
1440997580737.jpg -(163342B / 159.51KB, 483x572) Thumbnail displayed, click image for full size.
is mass M a sphere or a cylinder? that changes the moment of inertia and the angular momentum of mass M. you said no friction but it's rolling so I'm lead to believe we are operating under the rolling-without-slipping regime (translational speed 'v' = radius of the mass M 'r' x 'omega', the angular velocity).

set up a force diagram for the mass at location X. the weight force 'mg' points straight down, we'll split into components in a moment. The normal force 'N' of the hemisphere on mass M points radially outward (in this case north-east). We'll be solving for the condition where N --> 0 (i.e., it juuust loses contact with the hemisphere)

cont.
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Edwin Salpeter - Mon, 31 Aug 2015 01:26:04 EST OMGzRHpD No.55647 Reply
now the weight force 'mg' can be split into components. one component points radially inward from X with value mgcos(theta). the other component points in the direction of mass M's velocity vector, tangent to the hemisphere or south-east, with value mgsin(theta). the first component balances with the normal force N and provides the centripetal acceleration for mass M. the second component does the accelerating of mass M down the hemisphere.

As >>54457 said, now do the conservation of energy. The translational kinetic energy 1/2mv^2 plus the rotational kinetic energy 1/2Iomega^2 will equal mg(R-y) where y is the height of location X. if you want it dimensionless (R=1) then R-y = 1-sin(theta). make the v = r x omega substitution and solve for v.

the inward radial componenet mgcos(theta) provides the centripetal acceleration v^2/R. So mgcos(theta) = mv^2/R ... too distracted to finish the rest but solve for the max v that the inward radial component can still provide a = v^2/R, then you can solve for the value of cos(theta)

frikkin relativity

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- Sun, 02 Aug 2015 19:56:50 EST Du35j2Lj No.55576
File: 1438559810297.jpg -(295824B / 288.89KB, 1041x1041) Thumbnail displayed, click image for full size. frikkin relativity
This has certainly been asked here before but please help me understand this.
A space ship travels around earth near lightspeed. I understand that velocity makes
time aboard the ship seem slower to a spectator on earth. And when the ship stopped moving the crew would have aged less then this spectator. But here's what i dont get. Why does the spectators time also seem to move slower to the crew on the ship? Wouldnt earth look like someone pressed fast forward? But lets say earth time seems to move slower, what happens when the ship slows down, does light from everything that happened come towards it like a flash?
I know i sound dumb, but that's okay.
2 posts omitted. Click View Thread to read.
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Pierre-Simon Laplace - Mon, 03 Aug 2015 06:26:06 EST v2I6+0VG No.55579 Reply
That's not a dumb question at all. In special relativity, there is no preferred reference frame. If a rocket ship is travelling past the Earth, from the rockets perspective, the Earth is travelling past the rocket. So each will see the other's clocks as ticking slower to their own. This symmetry only holds for inertial reference frames though (no acceleration or deceleration). In your example, the space ship is constantly accelerating to move in a circle, and this destroys the symmetry. A more illustrative example is the one of the twin paradox. In the twin paradox, the ship leaves Earth and travels near the speed of light for a while and then turns around and returns to Earth. One twin is stays behind on Earth, and the other travels on the ship. The one who stayed behind on Earth has aged more than the voyager twin. It's a seeming paradox, because each twin witnesses the same thing: the other twin flies off at breakneck speed and returns at the same speed. The difference is that the space ship twin feels an acceleration. It's this acceleration that causes the jump in time - known as gravitational time dilation. This is an aspect of general relativity - beyond the scope of special relativity. So yeah, as soon as the ship starts accelerating or decelerating (as in your example), the events on Earth will play out in fast-forward from the ship's perspective.

https://en.wikipedia.org/wiki/Twin_paradox
https://en.wikipedia.org/wiki/Gravitational_time_dilation
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Grote Reuber - Mon, 03 Aug 2015 08:00:44 EST Du35j2Lj No.55580 Reply
>>55579

Thanks you! That clears my thoughts somewhat. It's still hard to grasp though.
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Fred Whipple - Tue, 25 Aug 2015 23:42:03 EST P+fSJ1RL No.55636 Reply
>>55580
Don't worry. Our brains didn't evolve with innate knowledge of spacetime. Our universe has been what we see for a long long time. Recent science and tools have shown us more cogs of the universe we may never have other wise been made aware of.

That people here can even explain these things is incredible in itself. SpaceTime is no simple algebra that's for sure.

Night v/s day

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- Mon, 24 Aug 2015 22:12:00 EST Fk84gn/u No.55620
File: 1440468720383.jpg -(149638B / 146.13KB, 778x740) Thumbnail displayed, click image for full size. Night v/s day
Hey, so just as here on earth we've got longer days in the summer and longer nights in winter, is there a possibility for a planet, any earth-sized planet, to have a 6 hour day and, I don't know, a 40 hour long night?
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James Mother Fucking Randi !lwriJ94kMg - Tue, 25 Aug 2015 05:31:05 EST yA35CPLh No.55625 Reply
This reminds me of Time cube for some reason.

Discuss...

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!oj3475yHBQ - Wed, 08 Jul 2015 20:14:54 EST NjsLJs2P No.55484
File: 1436400894839.jpg -(114479B / 111.80KB, 854x687) Thumbnail displayed, click image for full size. Discuss...
If time is equal to the distance that light travels, yet slows as one approaches the speed of light, does this not indicate that the speed of light is actually timeless?

If the speed of light is timeless, yet time is equal to the distance that light travels, does it not mean that the observer is responsible for the conception of distance in relation to light?

If time is equal to the distance that light travels, yet the speed of light is timeless, than space/time is actually light, as a measurement of time is actually a measurement of light.

If a measurement of time is actually a measurement of light, but the speed of light is timeless, does this not mean that to measure light is to create time?
20 posts and 2 images omitted. Click View Thread to read.
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Karl Jansky - Tue, 11 Aug 2015 09:12:09 EST YHjXylC8 No.55591 Reply
11.jpg -(80085B / 78.21KB, 666x69) Thumbnail displayed, click image for full size.
>>55589
>Theoretically, if one could obtain a unicorn that could wish you to the nearest star system...
Even your imaginary unicorn would have difficulty, the top equation is time dilation at constant acceleration.
c= the speed of light, v=velocity. If v<c, you end up with an imaginary number.
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Bernard Burke - Tue, 11 Aug 2015 22:36:58 EST 415JX8nG No.55592 Reply
>>55484
It's relative.
If you yourself are traveling the speed of light, the closer you get to c, the slower time gets for you only, the rest of the universe starts to fast forward.

I guess a photon itself would be a timeless object, it has to interact with something to change.. but nothing quantum mechanical exists singularly, it exists in the context of the nature around it.
I guess in photon time, the universe is only a tiny fraction of a second old, if that is even an accurate description.
But the rest of the universe still matters.

The way I think of quantum mechanical objects is that they aren't like a ball or anything concrete like that.
A beam of electromagnetic energy is like a river.
You can run up to it with a glass, take a scoop out, and proclaim you have an electron.
You are measuring the location of that electron, as it is in your hand, but it's not going anywhere. You could then spill that electron out of the glass, back into the river. Although you don't know where that electron is anymore, you could figure out what it's speed is and where it is likely going based on the contours of the river, or getting out of the metaphor, the physical nature of what is going on around it.

Photons are only timeless to themselves, the rest of the universe collapses any notion of them existing in a timeless place.
If light didn't exist in time, I imagine, if the universe was able to form in the first place, it would just look like a big clump of white noise
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Fritz Zwicky - Thu, 13 Aug 2015 19:25:39 EST BF8zYeiD No.55595 Reply
>>55592
It sounds like you have a pretty decent understanding of what you're talking about, and you're good at communicating those ideas understandably.

The Universe and Your Significance

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- Wed, 21 Jan 2015 17:42:34 EST 7UdqYDqD No.54926
File: 1421880154554.jpg -(416926B / 407.15KB, 2560x1440) Thumbnail displayed, click image for full size. The Universe and Your Significance
I've noticed this a lot when people take about outer space and the universe they always like to mention how "insignificant" it makes them feel.
"Yeah man space, wow, you know it really puts my life into perspective; how insignificant we are in the grander scheme of things."

This is my opinion but I think that's such a belittling thing to say its also unsettling how common it is a thing to say when talking about the universe.

Granted the universe is huge, and in comparison us tiny humans are very very tiny. Doesn't make us insignificant though, or our lives meaningless.
You are the most significant person in your life, because without you, your life wouldn't exist. Who cares if you don't become famous or invent something that changes the world, you are the universe experiencing itself through your life, defining it with every thought, action, emotion and experience you have.

Sure you are a tiny droplet in an ocean of water, however what is an ocean but a multitude of droplets?
43 posts and 5 images omitted. Click View Thread to read.
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Gerard Kuiper - Tue, 10 Feb 2015 17:00:43 EST KSSVR3HT No.55021 Reply
We can compare for significance if we want. Compared to a rock im significant, I think. But we dont know what is actually significant, because we dont know what the fuck is going on.
I certainly dont see any reason to believe that all of this is good or bad, significant or not, either way.
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Terror Incognito - Fri, 20 Feb 2015 15:22:25 EST 7DU4fAaH No.55056 Reply
1424463745712.jpg -(16755B / 16.36KB, 375x500) Thumbnail displayed, click image for full size.
>>54926

The fact that we're alive right now, able to experience and observe all that is in the universe makes us the most significant part of it, regardless of how small we appear to be on a specific scale of perception.

Time dilation and the Alcubierre drive

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- Thu, 30 Jul 2015 12:30:55 EST /fL15l2I No.55567
File: 1438273855753.jpg -(16840B / 16.45KB, 200x303) Thumbnail displayed, click image for full size. Time dilation and the Alcubierre drive
if one were traveling above c in a ship using an Alcubierre drive, would they experience time dilation?
as i understand it, the object affected by the drive isn't moving but rather space is simply expanding and contracting around it. the object has no velocity and isn't moving in the normal sense.
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Karl Swarzchild - Thu, 30 Jul 2015 13:05:05 EST lHGvTKQL No.55568 Reply
>>55567
No, because the entire ship is contained within it's own stationary spacetime bubble.

The negative time generated by dilation will only speed up the journey relatively to the speed of light.

Stephen Hawking - Aliens

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- Wed, 22 Jul 2015 09:52:58 EST eZ452btZ No.55537
File: 1437573178193.gif -(145178B / 141.78KB, 250x250) Thumbnail displayed, click image for full size. Stephen Hawking - Aliens
Discuss

http://m.space.com/29999-stephen-hawking-intelligent-alien-life-danger.html

http://news.bbc.co.uk/2/hi/8642558.stm
7 posts and 4 images omitted. Click View Thread to read.
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Alan Guth - Wed, 22 Jul 2015 16:29:07 EST YHjXylC8 No.55545 Reply
1437596947747.png -(60177B / 58.77KB, 740x391) Thumbnail displayed, click image for full size.
>>55543
>the stars we observe every night are already dead.
Unless you're using a telescope to look at galaxies very far away, they're all within a hundred thousand light years and probably aren't dead.

>>55544
Pic related is a much better explanation for UFOs.
>>
Johann Bode - Wed, 22 Jul 2015 17:08:26 EST 415JX8nG No.55547 Reply
>>55545
Hahaha that's awesome.
It would be an interesting statistic to see how the numbers change from populations with lots of alien cultural references to others were it's less prevalent, and how it changes with the scientific education levels of the respective populations effect the out come as well.

I've seen one ufo, it was probably a meteor, about twice the size of the full moon, comparable color and brightness, but it didn't have a tail and it flew right over me. I've seen large (good fraction of the full moon size) meteors before, and the big ones still had tails, but maybe it was a simple perspective issue, as the ones I saw with tails were all on the horizon. It still scared me though and I'm a super tough guy whose not afraid of anything

MFW

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- Thu, 16 Jul 2015 05:52:22 EST LD9WXxz6 No.55518
File: 1437040342119.jpg -(144755B / 141.36KB, 459x403) Thumbnail displayed, click image for full size. MFW
I realize we will never set it for ourselves.
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Alan Guth - Wed, 22 Jul 2015 08:35:39 EST YHjXylC8 No.55536 Reply
1437568539747.jpg -(1097252B / 1.05MB, 2400x2290) Thumbnail displayed, click image for full size.
>>55534
Yeah, but we're really far away too. If we were closer (and blocked out light from other sources, we see dim objects near very bright objects by covering up the bright object), some structures would be brighter, to an extent.
But nebulae are so big and diffuse they've be invisible up close. The face of OP's unicorn is about a light year long.

The IAU currently does not recognize space-unicorn as an alternative to light-year.
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William Huggins - Wed, 22 Jul 2015 16:49:15 EST rIYomINL No.55546 Reply
>>55534
That doesn't mean they aren't real or aren't visible light.
>>
Irwin Shapiro - Thu, 23 Jul 2015 00:48:39 EST OXINl/7g No.55549 Reply
>>55546
They're definitely *real*, but they're not as visible as the photos make them appear. Most of those awesome nebula photos are long exposures, yes, but they're also composites of infrared, x-ray, and visible light, with some coloration and hue/contrast added to make them "pop." It's a real thing in the photo, but it's not the "natural" way it looks.

the sun has fallen down

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- Tue, 16 Jun 2015 22:13:13 EST fhuRENSe No.55412
File: 1434507193485.png -(22297B / 21.77KB, 411x411) Thumbnail displayed, click image for full size. the sun has fallen down
what would happen to the earth and the rest of the pack in the system if suddenly the sun dissapeared? how quickly would the planet freeze?
6 posts and 2 images omitted. Click View Thread to read.
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Thomas Gold - Wed, 15 Jul 2015 23:13:49 EST 415JX8nG No.55517 Reply
>>55416
If my imagination is allowed to run wild, I would put the earth in orbit around Jupiter, close enough to cause a decent amount of geologic activity and keep some sort of an atmosphere, even if it's toxic and much less dense than ours is today.

The center piece of civilization would probably be fusion/fission nuclear reactors, we could mine hydrogen from Jupiter. But we would need manufacturing hubs, mines, and genetically modified plants in vertical farms. I think it might be best to put residential areas around hydrothermal vents. But the other stuff will probably need to be above ground

Gentlemen...

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- Tue, 14 Jul 2015 22:24:03 EST lHGvTKQL No.55511
File: 1436927043339.jpg -(10788B / 10.54KB, 512x480) Thumbnail displayed, click image for full size. Gentlemen...
BEHOLD!

The mission was a success.

We have a picture of Pluto now.
5 posts and 2 images omitted. Click View Thread to read.
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Pierre-Simon Laplace - Fri, 17 Jul 2015 14:53:48 EST P+fSJ1RL No.55520 Reply
>>55514
I love that they call it Mordor. It so perfectly marks the time table of our exploration beyond our world. All planets in our system maintain old Latin names of old gods and deities. Now one holds a name from almost 100 years ago and has a region photographed and named Mordor.

Wonder if we find any other sneaky moons around the Jovians what will the names be?
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Pierre-Simon Laplace - Fri, 17 Jul 2015 14:55:42 EST P+fSJ1RL No.55521 Reply
>>55520
derp charon has mordor and was discovered only just back in 78. Didn't mordor exist in tolkiens books by then? What ever still impressed by the difference in names in system based on time discovered. nb
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Alan Guth - Fri, 17 Jul 2015 20:19:27 EST okoywjgZ No.55524 Reply
1437178767194.jpg -(30206B / 29.50KB, 636x318) Thumbnail displayed, click image for full size.
>>55520
I hope it becomes official some day, it also fits the underworld theme the IAU wants

Here's a map of Pluto with names suggested by NASA

Venus and Jupiter June 2015

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- Sun, 21 Jun 2015 23:01:02 EST Mx4j4tsI No.55436
File: 1434942062578.jpg -(34158B / 33.36KB, 560x475) Thumbnail displayed, click image for full size. Venus and Jupiter June 2015
The best view in northern hemisphere for June, and not ONE thread about it?
Where are all my Venus and Jupiter observers at?
15 posts and 7 images omitted. Click View Thread to read.
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Chushiro Hayashi - Sun, 28 Jun 2015 17:16:18 EST jOF47H5F No.55465 Reply
>>55464
>He stole his data from Tycho.

In the end that's ultimately what he had to do, but you're conveniently disregarding everything he went through up until that point. Maybe you should read up about the man some time.
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Karl Jansky - Fri, 03 Jul 2015 18:44:29 EST 0TqljQT/ No.55467 Reply
>>55465
No. He didn't have to do anything, he chose to. Just as you chose to neglect the fact his data was stolen and accuse me of ignoring history. Pot? Black?
Personal difficulty does not change the facts, Kepler was brilliant but the data was stolen.

And no the sentence "the universe is a high-dimensional object constantly rotating within itself" isn't going to cause anyone to stumble onto some new cosmology, it's so vague it doesn't many anything, it's technobabble.
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Tadashi Nakajima - Thu, 06 Apr 2017 14:34:06 EST S0k+HZwt No.56907 Reply
>>55467

Yes, some things you morally HAVE to do(would you watch your significant other (or self) be tortured over and over again, while unbound and free with a cell phone? No you'd be compelled to do something different, or your guilty of doing nothing when a huge injustice is being done(injustice is an open ended term I know) and you can do something about it... Or guilty of being a sadist/masochist.

The shape of Galaxies.

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- Sun, 14 Jun 2015 00:27:54 EST kfQx+w9j No.55402
File: 1434256074283.jpg -(638900B / 623.93KB, 1920x1200) Thumbnail displayed, click image for full size. The shape of Galaxies.
So if I'm correct, every galaxy has a supermassive black hole at the center of it. Every galaxy was once an active Quasar and then cooled after the black hole at the center of the galaxy spewed and consumed all the matter around it. So if a black hole has angular momentum at the center of a galaxy, does that mean the galaxy would result in a spiral shape? And would non rotating black holes instead form more of an irregular galaxy shape? I'm thinking in terms of galaxy evolution and the various shapes different galaxies take. Cheers.
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Roger Penrose - Sun, 28 Jun 2015 09:38:23 EST IQY0YtFB No.55461 Reply
Eventually the spiral forms take shape of malicious code and Avira antivirus will detect them as false positives, You should try a Linux Distro, OP.
Just sayin'
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Kiyotsugu Hirayama - Sun, 28 Jun 2015 14:38:04 EST L3OB90Tk No.55463 Reply
>>55441
>>55446

You're both sort of right. Before major mergers when galaxies shave a lot of gas and are actively forming stars most of the big ones are spirals, some of the small ones can be irregular bit that's a different story. Left to it's on devices a spiral will not evolve or normalise into an elliptical.

A major merger is when two roughly equally sized galaxies collide and merger. It is believed elliptical form major mergers of spirals. As part of this merger the gas is usually stripped out and star formation shuts down with nothing to make stars out of (After the merger is finished). When it reaches a steady state it will be an elliptical, it will not evolve back into a spiral. The reason ellipticals have older stars is because they don't form any new ones, the oldest stars in each galaxy will not be significantly older or younger than the other.

>>55431

Frame dragging is a tiny effect, it doesn't affect things like that.

Aw Shit

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- Wed, 17 Jun 2015 17:51:11 EST KlwZpL5U No.55418
File: 1434577871926.jpg -(325142B / 317.52KB, 650x488) Thumbnail displayed, click image for full size. Aw Shit
I just started work at MIT, working on the Transiting Exoplanet Survey Satellite [TESS] program. Ask me stuff about space & shit, I can answer it for you.
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Fred Hoyle - Fri, 19 Jun 2015 06:44:57 EST YHjXylC8 No.55426 Reply
1434710697724.png -(795268B / 776.63KB, 1259x696) Thumbnail displayed, click image for full size.
Do you feel the current method of detecting planets in the habitable zone is exhaustive enough to extrapolate an upper bound on how frequently rocky planets where water exists in all three phases occur, at least for certain classes of stars?

Also, did you get a cool mission patch?
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William Herschel - Fri, 19 Jun 2015 22:26:23 EST KlwZpL5U No.55427 Reply
>>55426
Good question!
This mission is designed to find candidate star systems for follow up observation by more sophisticated telescopes, like the JWST or GMT. What this means is that our mission is to simply characterize and catalogue as many candidate systems as possible. After speaking with a professor on the program yesterday, he explained that simulations of one year of operation showed a potential catologue of up to 75 earth mass exoplanets, up to 150 between earth and Neptune mass, and more in the Jupiter size class.
However, These candidates are going to be in orbit around the best candidate stars for water to exist, namely red dwarfs and smaller main sequence stars. It is hard to say which ones could have all three phases. At least what TESS can tell you is the mass, period, and a brief sniff of the atmosphere (if you subtract the star spectra before a transit from the spectra during a transit, you get a vague idea of the atmosphere composition).

Alas I have not gotten my patch yet. I'm hoping to score a TESS patch and a CHANDRA patch, cause that's' another one of our missions.
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William Herschel - Fri, 19 Jun 2015 22:27:25 EST KlwZpL5U No.55428 Reply
I'm also on my phone, so, sorry for the wall of text with no format.
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