Staring at a Red Dwarf harmful?


by AndromedaRXJ
Tags: dwarf, harmful, staring
AndromedaRXJ
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#1
Apr11-13, 07:33 PM
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If we lived in a solar system with a red dwarf, and it had the same apparent size as the Sun, would it be harmful for our eyes to look at?

If not, then how much closer would you have to get?

Just curious, and I might use this info for fiction.
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Mordred
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Apr11-13, 10:06 PM
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The habitable zone for a planet would have to be much closer.
The HZ zone for a planet with a Red dwarf sun with a luminosity of 0.02 the HZ would be roughly 0.14 the distance between Earth and our own sun.
the visual L isn't hazardous to the eyes unless one considers the HZ distance. Although red dwarfs produce high X UV radiation. Much of that can be filtered out by atmosphere.

However the closeness of the HZ is in high risk of stellar activity such as solar flares etc.
Mordred
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Apr11-13, 10:39 PM
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I located the article that I recalled that HZ distance from.
http://arxiv.org/abs/0901.1860

mfb
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#4
Apr13-13, 12:00 PM
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Staring at a Red Dwarf harmful?


Stars with 2% the solar luminosity have a surface temperature of ~3400K, or ~1/16 times the brightness of sun. I would expect that this is still dangerous.
Vanadium 50
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#5
Apr13-13, 12:30 PM
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Looking at the sun during an eclipse is dangerous - I can't imagine looking at a redder star without a moon in front of it could possibly be less dangerous.
Mordred
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Apr13-13, 04:14 PM
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Look at a candle flame long enough can be harmful to the eyes. If I misimplied that in my earlier post that was not my intention.
Bandersnatch
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#7
Apr13-13, 04:38 PM
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Quote Quote by Mordred View Post
Although red dwarfs produce high X UV radiation.
Wait, why is that? Shoudn't they have the radiation spectrum shifted towards infrared, rather than UV?(as compared to the Sun). It is a black body spectrum, after all - or so I thought.
Mordred
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Apr13-13, 05:00 PM
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The high X UV is created during flare ups I was going to post another article that mentions it but I'm having trouble getting the link to work from my phone lol
Bandersnatch
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Apr13-13, 05:39 PM
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Quote Quote by Mordred View Post
The high X UV is created during flare ups I was going to post another article that mentions it but I'm having trouble getting the link to work from my phone lol
I swear you've had this article linked here just a moment ago, but now you don't:
http://www.as.utexas.edu/astronomy/e...calo/heath.pdf

Maybe it's my saturday's altered sobriety playing funky games with my brain, but assuming that you had, then it(the paper) seems to say that during the largest flares the UV band irradiation merely reaches the regular, quiescent levels we get from the Sun:

We put the biological implications of observed increases in stellar UV during
flares in perspective by pointing out that the quiescent UV outputs of dMe stars
are very low compared with the Sun. Using data from Worden et al. (1984), YZ
Canis Minoris (Teff = 3097 K) has a total luminosity around 0.01 L⊙ , but in the
U-bandpass it is not quite 2.0 × 10−4 as luminous as the Sun. For a planet receiving
Ie (0.10 AU), the U-bandpass output of YZ Cmi would have to rise by a factor of
50 (4.2 stellar magnitudes) for incident UV-A to match that arriving continuously
at the top of the Earth’s atmosphere from the quiescent Sun. UV Ceti with less
than 3.0 × 10−3 L⊙ (Leggett et al., 1997) has a quiescent U-bandpass output some
1.1 × 10−5 that of out Sun (Lacy et al., 1976). A U-bandpass upsurge of over 260
times (>6.0 magnitudes) would be necessary before incident U-bandpass radiation
matched continuous Earth values at the Ie radius of 0.05 AU). Moreover, even
when flare UV exceeds the latter, it may be maintained for only a short time. UV
Ceti flare stars, as a typical example (described by Mochnacki and Zirin, 1980),
generally rise to a peak within 10 s and declined substantially within about 20 sec).
The quiescent U-bandpass component of insolation from AD Leonis (Teff = 3400
K), is just 0.03 solar at the Ie radius (0.15 AU). The ‘Great Flare’ of April 12,
1985 exceeded 4.6 magnitudes (an increase by a factor of >60) in the U-bandpass,
so UV-A at the Ie radius would have climbed to the continuous Earth level within
about 8 min, peaked sharply at 1.8 times the Earth level at 10 min, and fallen
below Earth level after 18 min.
Mordred
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Apr13-13, 06:05 PM
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Yeah that was the article for some reason it was linking wrong when I used my phone.

Thanks for the clarification on the UV levels I was wondering on that myself hence looking for other references
AndromedaRXJ
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Apr13-13, 07:28 PM
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Quote Quote by Vanadium 50 View Post
Looking at the sun during an eclipse is dangerous - I can't imagine looking at a redder star without a moon in front of it could possibly be less dangerous.
If it's a total eclipse, you can stare at it though. Can't you?

Quote Quote by Mordred View Post
Look at a candle flame long enough can be harmful to the eyes. If I misimplied that in my earlier post that was not my intention.
Well of course. I can imagine, any light source can be harmful with the right distance and time.

But with the Sun, it doesn't take very long at all to be harmful. So I'm wondering how a red dwarf, with the same apparent size, would compare.
Vanadium 50
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#12
Apr13-13, 08:11 PM
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Quote Quote by AndromedaRXJ View Post
If it's a total eclipse, you can stare at it though. Can't you?
Well, you can, I suppose. Doesn't mean you should. 1% of the sun is more than enough to cause eye damage.


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