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Betelgeuse captured by ALMA

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Re: Betelgeuse captured by ALMA

#51
post #38

That's amazing resolving power, even if it's been done (maybe not in the exact same way) for quite a while now. Hopefully newer telescopes like the James Webb Telescope will be able to resolve even the _planets_ around other stars, which we are already able to do with the biggest of exoplanets today (good example -> [1]). [1] http://phenomena.nationalgeographic.com/files/2014/05/1RSX_J...

Keep in mind that JWT is a space-based telescope and ALMA is ground based (and an interferometer, not a single dish).

Used JWT more as an example of increasingly advanced telescopes, not as a specific type of telescope, but maybe it wasn't the best example...

Re: Betelgeuse captured by ALMA

#52
post #17

A 1.64 billion km diameter sphere 600 light years away will have an apparent width of 2.9 x 10^-7 radians. That's roughly equivalent to looking at an object 250nm wide at arm's length. A red blood cell is approximately 8000nm wide. Crazy resolving power.

Optical interferometers have resolved Betelgeuse down to 9 milliarcseconds (4 x 10^-8 radians), so this isn't even the highest resolution image yet of this star[1].

[1] http://blogs.discovermagazine.com/badastronomy/2010/01/12/sp...

Re: Betelgeuse captured by ALMA

#53

Earlier quoted context omitted.

What is the right way to think about this? If we observe a supernova 600LY away, do we say that event is happening "now" from our frame of reference? Or should we think of it as happening "600 years ago", and the light from the event is only now reaching us? If you think of causality itself moving at the speed of light (which of course it does), and think in light cones rather than referring to a nonexistent universa…

It is happening in our NOW and that's all that matters from a cosmic perspective, since no signal can travel faster than light. In that sense there's only the NOW, even when you're observing your friend a few meters away. We might say that physics itself travels at light speed.

I think even that undersells it. Existence itself moves at light speed.

Re: Betelgeuse captured by ALMA

#55

That's amazing resolving power, even if it's been done (maybe not in the exact same way) for quite a while now. Hopefully newer telescopes like the James Webb Telescope will be able to resolve even the _planets_ around other stars, which we are already able to do with the biggest of exoplanets today (good example -> [1]). [1] http://phenomena.nationalgeographic.com/files/2014/05/1RSX_J...

That image is quite stunning. As the 2008 press release [1] states, this image was one of the first successes at direct imaging an exoplanet. It raised some interesting questions, such as why such a massive planet could be found so far out (330 AU!) The scientific paper for this observation can be found in [2] for those interested more astrophysical detail.

I feel compelled to offer an astronomer's clarification though. The planet in this image is not "resolved" in the technical sense. A resolved image usually means that fine details about the object are discernible spatially. For example, unresolved images of Betelgeuse provide a point source image, without details; a resolved image of Betelgeuse allows you to find spatial features such as that enormous bubble. Another example is, say, Jupiter: by eye or with a very modest telescope, Jupiter is a (bright) point of light. But with a moderate increase in resolving power, you can see all sorts of interesting features, such as the Great Red Spot, and the various cloud layers that vary with latitude.

Individual exoplanets are simply too small to resolve, even with JWST. Even being generous - assuming that the planet is bright enough to detect and that the host star doesn't overwhelm the signal - the angular sizes of exoplanets are miniscule. Lets assume some very generous numbers: a hypothetical exoplanet ten times the diameter of Jupiter (very large), and very, very close to Earth - let's say, 10 lightyears for simplicity and generosity. In arcseconds, the angular diameter of such an object on the sky is about 0.003". Smaller planets at more reasonable distances are even smaller. (The angular size of an object is just small angle trigonometry: in radians, about the width of the object divided by its distance.) Currently, science-class telescopes usually require about 1" resolution. JWST has about 0.1" resolution [3]; an interferometer like ALMA can, at its very best, achieve maybe 0.02" [4], though interferometers (as mentioned in other answers) sacrifice some things in exchange for spatial resolution.

This isn't to say you can't just detect exoplanets - you can, even with a ground based telescope like Gemini - but you probably won't resolve them, at least in this generation of telescopes, including JWST. But you can do a lot without spatial resolution - for example, you don't need to resolve the object to measure its spectrum, and spectral analysis can tell you a great deal.

[1] http://www.gemini.edu/sunstarplanet [2] https://arxiv.org/abs/0809.1424 [3] https://jwst.nasa.gov/faq.html#webbbetter (question 25) [4] https://almascience.eso.org/about-alma/alma-basics (section: spatial resolution)

Re: Betelgeuse captured by ALMA

#56
post #27

At the risk of uncovering my ancientness, I remember reading astronomy books as a kid which specified that stars are so far away that they can't appear as anything more than dots of light even when viewed through the largest telescopes. Always makes me wonder what can be achieved in the future, especially since we're probably somewhere on an exponential progress curve. Of course, assuming a lot of optimism about not…

I think it was in Cixin Liu's 'The Dark Forest' where there's a giant telescope at the edge of the solar system with twelve independently floating lenses focused and corrected by tiny thrusters...

What a terrible book. Naively written, leaves the impression that the author is more showing off that he can write about every sci-fi meme in existence ("I'm a big boy now, I know about that topic too!"). Unfocused, meandering plot. Nonsensical end. I regret wasting my time with it.

Re: Betelgeuse captured by ALMA

#57
post #27

At the risk of uncovering my ancientness, I remember reading astronomy books as a kid which specified that stars are so far away that they can't appear as anything more than dots of light even when viewed through the largest telescopes. Always makes me wonder what can be achieved in the future, especially since we're probably somewhere on an exponential progress curve. Of course, assuming a lot of optimism about not…

Regarding visible spectrum observations, I've been waiting to see if anyone can come up with a way to develop a consumer-accessible instrument that can sample a high enough resolution, to image all of the moon landing sites. For as long as I can remember, the same thing has been said about the surface of the moon, which is the primary fuel for hoax narratives. With all the buzz about high-resolution arrays being cobb…

Interesting read on the subject of capturing the lander sites: http://curious.astro.cornell.edu/about-us/45-our-solar-syste...

Re: Betelgeuse captured by ALMA

#58

That's amazing resolving power, even if it's been done (maybe not in the exact same way) for quite a while now. Hopefully newer telescopes like the James Webb Telescope will be able to resolve even the _planets_ around other stars, which we are already able to do with the biggest of exoplanets today (good example -> [1]). [1] http://phenomena.nationalgeographic.com/files/2014/05/1RSX_J...

That image is quite stunning. As the 2008 press release [1] states, this image was one of the first successes at direct imaging an exoplanet. It raised some interesting questions, such as why such a massive planet could be found so far out (330 AU!) The scientific paper for this observation can be found in [2] for those interested more astrophysical detail. I feel compelled to offer an astronomer's clarification thou…

I think maybe your definition of "resolved" is a little skewed. It is not about the features of the object, but more by the Rayleigh Criterion [1][2]

So we can already (and have been able to for a long time) to "resolve" things as apparently-small as exoplanets, but for resolving _surface details_ we are one order of magnitude away for interferometers and two orders of magnitude away for standard single-mirror telescopes. Right?

[1] https://en.wikipedia.org/wiki/Angular_resolution#Explanation [2] Lord Rayleigh, F.R.S. (1879). "Investigations in optics, with special reference to the spectroscope".

Re: Betelgeuse captured by ALMA

#59
post #46

Earlier quoted context omitted.

IIRC we're talking about it reaching apparent magnitude ~ -12, given or taken a couple magnitudes (or about as bright as the full Moon - Just imagine that much light coming from an infinitely tiny dot instead). BTW with a declination of ~ +7° Betelgeuse is very close to the celestial equator, so the supernova will be visible from anywhere on Earth, save a very small region within 7° from the South Pole.

It's fun to ponder how it will be that bright at every point that is the same distance. Imagine a sphere centered on Betelgeuse with a 600 light year radius with Earth on the surface of this sphere. The fact that enough photons reach my eyeballs to be able to see it at night is difficult to comprehend - the amount of energy needed to sprinkle every square millimeter of a sphere that size is just unimaginable. Now mak…

Rigel, the blueish star on the other side of Orion, is a bit brighter (magnitude 0.13 vs. 0.5), and is a bit further away (860 ly vs. 640).

Re: Betelgeuse captured by ALMA

#60

Something about the contrast in the image makes it seem to "pulse" as I look at it...eerie! Edit: Maybe it's just the coffee I drank?

I sort of see it too.

I think it's caused by a mix of 2 things, first when you stare at something for a while the details tend to fade away, and this image is very susceptible to it since it has very soft colors on the border, and the gradients are from the outside towards the inside so that causes the perceived object to shrink. Second, the eye constantly has small involuntary saccadic movements, and whenever that happens the first effect gets "reset", and the perceived image grows to its real size again.

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