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midtskogen
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04 Jun 2017 09:06

Is it possible to watch Betelgeuse close up (say, from a distance where its diameter is 5 degrees) with the unprotected eye?  I did some very quick calculations, and the density near Betelgeuse's fuzzy edge is very low, similar to that of a hydrogen balloon far up in Earth's atmosphere (assuming uniform density, so the density is surely lower), so how much can it really glow?

The sun is about 8*1010 times brighter than Betelgeuse in the sky.  But the sun's area is about 3.4*109 times larger in the sky (angular radius 800" vs 0.0275").  So, this should make the Betelgeuse's surface 4% as bright as the sun's.

In the movie Sunshine the computer tells Searle that he will receive permanent eye damage above 3.1% when he wants to look at the sun close up in all its glory.  So he asks for 3.1% for 30 seconds.  Clearly, it wasn't very healthy.

I guess the answer to my original question is clearly no.  Perhaps it's possible to endure the sight for a second with powerful sunglasses.  The heat radiation would be intense, though.
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04 Jun 2017 09:34

midtskogen wrote:
Is it possible to watch Betelgeuse close up (say, from a distance where its diameter is 5 degrees) with the unprotected eye?  I did some very quick calculations, and the density near Betelgeuse's fuzzy edge is very low, similar to that of a hydrogen balloon far up in Earth's atmosphere (assuming uniform density, so the density is surely lower), so how much can it really glow?

The sun is about 8*1010 times brighter than Betelgeuse in the sky.  But the sun's area is about 3.4*109 times larger in the sky (angular radius 800" vs 0.0275").  So, this should make the Betelgeuse's surface 4% as bright as the sun's.

In the movie Sunshine the computer tells Searle that he will receive permanent eye damage above 3.1% when he wants to look at the sun close up in all its glory.  So he asks for 3.1% for 30 seconds.  Clearly, it wasn't very healthy.

I guess the answer to my original question is clearly no.  Perhaps it's possible to endure the sight for a second with powerful sunglasses.  The heat radiation would be intense, though.

I made some calcualtions as well.
  • Betelgeuse's size: Wikipedia tell that Betelgeuse is estimated at 887 Solar radii, so its diameter is 1.234.171.800 km
  • Distance: With this radius and at an angular size of 5°, the distance is about 14.134.000.000 km, or 0.0015 ly (http://www.1728.org/angsize.htm)
  • Luminosity: Wikipedia says the Absolute Magnitude of Betelgeuse is around -5.85
  • Magnitude: At this luminosity and distance, Betelgeuse's mangitude would be in the ballpark of -27.537 (http://www.1728.org/magntudj.htm)
The Sun's apparent magnitude from Earth is -26.74, 2 times fainter, so yeah, you probably shouldn't look at it.
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04 Jun 2017 15:16

According to Mr.Eclipse, 

The luminous transmittance of the filter, when determined as described in clause 6 of EN167, shall not exceed 0.0032%. Filter transmittance in the waveband 280 to 380 nm (ultraviolet radiation) shall not exceed 0.003% at any wavelength. Transmittance in the near infrared waveband (780 to 1400 nm) shall not exceed 0.027% at any wavelength. Filters with luminous transmittance (in the waveband 380 to 780 nm) equivalent to scale number 12 to 16 as specified in Table 1 of EN169:1992 are considered suitable for direct observation of the sun. It should be noted that many observers will find the solar image uncomfortably bright when filters with scale numbers of 12 or 13 are used.


A filter which transmits 4% of the sunlight is roughly equivalent to a neutral density filter ND 1.4, or welder's glass #4.  Definitely not good enough.  For comparison, #12 transmits just 0.002% of the light, and #13 is 0.0007%.  So looking at Betelgeuse from up close would be very painful, you would not see any details, and gazing for too long will blind you.

A more insidious part of this is the infrared, which we are underestimating because it does not count to the visual magnitude but still damages the retina.  The surface temperature of Betelgeuse is about 3500K, compared to 5770K for the Sun, so the ratio of surface flux (intensity over all wavelengths) is that ratio to the 4th power, which is 13.5%.  That's like looking at the Sun with Welder's glass #3 or neutral density filter ND 0.9.  Don't do it.

I guess this naturally leads to the question -- what filter would you need to safely look at Betelgeuse from up close?  Since we're starting at 13.5% of the Sun's surface brightness, we must use a filter that transmits 0.014% of that to be the equivalent of looking at the Sun through a #12 shade. So we need a #10 shade at least to safely look at Betelgeuse!
 
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04 Jun 2017 22:22

midtskogen wrote:
Source of the post In the movie Sunshine the computer tells Searle that he will receive permanent eye damage above 3.1% when he wants to look at the sun close up in all its glory.  So he asks for 3.1% for 30 seconds.  Clearly, it wasn't very healthy.

Also, keep in mind that at the start of the movie, the Icarus II is already nearing Mercury (the computer itself says 63 million miles), so the Sun's luminosity at that point is almost 670% of the one from Earth. 3.1% there equals 20% here.


Btw, I love that movie.
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05 Jun 2017 03:00

XBrain130 wrote:
Source of the post Also, keep in mind that at the start of the movie, the Icarus II is already nearing Mercury (the computer itself says 63 million miles), so the Sun's luminosity at that point is almost 670% of the one from Earth. 3.1% there equals 20% here.

The total luminosity, but the surface luminosity remains the same.  The larger the sun, the more retina area the sun will spread over.  You damage your eyes if you look at a welding light even though the total luminosity is less than the entire daytime sky.  So I think there are two thresholds of damage, one for exposure / area and one for total exposure.
XBrain130 wrote:
Source of the post Btw, I love that movie.

The first half is beautiful, the second half is *facepalm*-
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05 Jun 2017 10:22

midtskogen wrote:
Source of the post The first half is beautiful, the second half is *facepalm*-

agree, it could be science related but then turned to horror-fiction thing
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05 Jun 2017 23:49

The story and the science were awful, but I liked the movie throughout for its visual style and music/sound design, and how they used the lighting and color palette to affect the mood in different scenes.  It's a surprisingly artsy film if you ignore the slasher-horror dumbness.
 
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06 Jun 2017 10:41

Watsisname, i am not an expert, but such a thing that happend in the movie to the sun could happen in reality?
it doesnt make sense to me that the sun will be colder (like out of fuel or something)
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06 Jun 2017 11:54

Spacer wrote:
Watsisname, i am not an expert, but such a thing that happend in the movie to the sun could happen in reality?
it doesnt make sense to me that the sun will be colder (like out of fuel or something)

Yeah, normally a main sequence star get brighter and hotter as it ages, and certainly there isn't much change in 50 years.
From what I understood reading on internet (in-universe it wasn't mentioned at all), it only happened in the movie because a lump of exotic matter called Q-ball formed inside the sun and interferred with the nuclear fusion. That's what they were aiming the megabomb at. Of course it means that the entire thing is pure speculation, which would explain why Capa kept saying that they had absolutely no certainty that they could succeed.
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06 Jun 2017 12:11

The movie's science advisor Brian Cox suggested that this could happen if turns out that the sun contains a Q-ball.  I suppose the script said that the sun had to be dying, and Cox had to come up with a plausible scientific scenario for it.  However, there is no evidence that the sun or any other star contains such a thing that will cause a premature star death.
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06 Jun 2017 14:22

I have a question.

Why there are negative stellar parallaxes? what does that mean?
 
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06 Jun 2017 15:15

Massive stars typically live for a few million years, so how come so many can be found outside the galaxy in SE (typically near the central bulge, seen in the image) if the distance required to travel is longer than their lifespan? Also how can massive stars be distributed in a galaxy were they aren't near their stellar siblings/nursery due to their short lives? Am I overestimating?
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06 Jun 2017 19:47

Watsisname wrote:
Source of the post O's and B's aren't shown here and are generally thought to lack these surface features

So their photosphere is featureless? Do sunspots even exist on such hot stars?
 
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06 Jun 2017 21:54

FastFourierTransform wrote:
Source of the post Why there are negative stellar parallaxes? what does that mean?

If the light from a distant star is bent by a foreground object with measurable parallax, the parallax of the distant star could appear negative.
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07 Jun 2017 00:12

FastFourierTransform wrote:
Source of the post Why there are negative stellar parallaxes? what does that mean?

Which catalog, and how negative is it?  If it's only slightly negative then the reason is probably uncertainty.  Parallax angle should approach zero as the distance of the star goes to infinity, but since these are measurements, and every measurement has some uncertainty, sometimes the raw data produces an answer that is slightly negative.

It would be like measuring a mass to be -0.1 +/- 0.2 grams.  You know a negative mass makes no sense, but what this result actually means is that it is indistinguishable from zero.


midtskogen wrote:
If the light from a distant star is bent by a foreground object with measurable parallax, the parallax of the distant star could appear negative.


This is generally unimportant in the context of measuring stellar parallaxes -- lensing is just too weak on those scales.  It's more important for microlensing events (which just brightens the star rather than displacing it), or for distorting images of galaxies in clusters.  The Sun also does this measurably (the famous eclipse test for general relativity), but we don't measure parallaxes when stars are anywhere near the Sun.


spaceguy wrote:
Source of the post Massive stars typically live for a few million years, so how come so many can be found outside the galaxy in SE (typically near the central bulge, seen in the image) if the distance required to travel is longer than their lifespan? Also how can massive stars be distributed in a galaxy were they aren't near their stellar siblings/nursery due to their short lives? Am I overestimating?

It's just how the current generation system works.  Space Engine generates stars using the initial mass function (so it has the correct relative abundance of stars by mass), but it does not say "here's where star formation regions are" and determine how to place massive stars relative to them.

spaceguy wrote:
Source of the post So their photosphere is featureless? Do sunspots even exist on such hot stars?

More or less and probably not. There is ongoing study as to what their photospheres are like and what roles magnetic fields might play, but we don't think they have sunspots like the cooler stars do.  You'll find there are no sunspots on hot stars in Space Engine either.

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