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Old 03-04-2003, 01:32 PM
Jaak Suurpere
 
Posts: n/a
Default New Alpha Centauri data

Erik Max Francis wrote in message ...
Jonathan Silverlight wrote:

It's interesting to compare that with the depiction in David Hardy's
painting "Proxima's Planet" - I've got the print over my desk. He
shows
them in a dusty red sky, which makes sense as -6 stars would be
visible
in daylight even on Earth with our blue sky, but they are about one
inch
(2.5 cm) apart which corresponds to at least a couple of degrees at
normal viewing distance.


But this only takes into account the brightness of the A and B
components. Proxima itself would be very bright, because for it to be
in the habitable zone (presuming that's where it is, I'm not familiar
with the painting), the planet needs to be very close to Proxima. For
it to be in the habitable zone, in fact, it needs to be at a position
where the intensity of sunlight is the same as at Earth's orbit, which
means that Proxima will have the same brightness as the Sun, about
magnitude -27 -- a little less because Proxima has enough infrared
excess that that will go into heating the planet a little, requiring
less raw illumination in the form of visible light.

Do you have any idea how much less?

A and B will be easily visible, but most of the illumination will come
from Proxima itself. It will be a cool, red light, but it will be
nearly as bright as the Sun on a full day. Almost by definition.


How large bolometric correction towards red would be acceptable for
terraforming?

On Earth, temperate and tropical shadow-tolerant land plants
habitually grow in 1/100 of total sunshine. Indeed, photosynthesis
suffers from "light inhibition". But what light they do get has a lot
of blue (scattered from sky) or at least red (filtered through leaves
of other plants).

How low light temperature can plants evolved on Earth endure? And what
would be the corresponding bolometric correction?

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Old 04-04-2003, 05:44 AM
Erik Max Francis
 
Posts: n/a
Default New Alpha Centauri data

Jaak Suurpere wrote:

Do you have any idea how much less?


Someone else compared the bolometric magnitudes, which is a pretty good
first order approximation (the total influx of stellar energy would be
the same, but a red star would appear significantly dimmer than a yellow
one). By that reckoning it would be a difference of about 4 magnitudes
(less than a factor of 100 in illumination), but that only brings the
the magnitude from -27 to something like -23.

How large bolometric correction towards red would be acceptable for
terraforming?


I have no idea.

--
Erik Max Francis / / http://www.alcyone.com/max/
__ San Jose, CA, USA / 37 20 N 121 53 W / &tSftDotIotE
/ \ Listen to my song
\__/ Chante Moore
Lsystem / http://www.alcyone.com/pyos/lsystem/
A Lindenmayer systems explorer in Python.
  #3   Report Post  
Old 20-04-2003, 03:08 PM
Jaak Suurpere
 
Posts: n/a
Default New Alpha Centauri data

Erik Max Francis wrote in message ...
Jonathan Silverlight wrote:

It's interesting to compare that with the depiction in David Hardy's
painting "Proxima's Planet" - I've got the print over my desk. He
shows
them in a dusty red sky, which makes sense as -6 stars would be
visible
in daylight even on Earth with our blue sky, but they are about one
inch
(2.5 cm) apart which corresponds to at least a couple of degrees at
normal viewing distance.


But this only takes into account the brightness of the A and B
components. Proxima itself would be very bright, because for it to be
in the habitable zone (presuming that's where it is, I'm not familiar
with the painting), the planet needs to be very close to Proxima. For
it to be in the habitable zone, in fact, it needs to be at a position
where the intensity of sunlight is the same as at Earth's orbit, which
means that Proxima will have the same brightness as the Sun, about
magnitude -27 -- a little less because Proxima has enough infrared
excess that that will go into heating the planet a little, requiring
less raw illumination in the form of visible light.

Do you have any idea how much less?

A and B will be easily visible, but most of the illumination will come
from Proxima itself. It will be a cool, red light, but it will be
nearly as bright as the Sun on a full day. Almost by definition.


How large bolometric correction towards red would be acceptable for
terraforming?

On Earth, temperate and tropical shadow-tolerant land plants
habitually grow in 1/100 of total sunshine. Indeed, photosynthesis
suffers from "light inhibition". But what light they do get has a lot
of blue (scattered from sky) or at least red (filtered through leaves
of other plants).

How low light temperature can plants evolved on Earth endure? And what
would be the corresponding bolometric correction?
  #4   Report Post  
Old 26-04-2003, 02:31 PM
Erik Max Francis
 
Posts: n/a
Default New Alpha Centauri data

Jaak Suurpere wrote:

Do you have any idea how much less?


Someone else compared the bolometric magnitudes, which is a pretty good
first order approximation (the total influx of stellar energy would be
the same, but a red star would appear significantly dimmer than a yellow
one). By that reckoning it would be a difference of about 4 magnitudes
(less than a factor of 100 in illumination), but that only brings the
the magnitude from -27 to something like -23.

How large bolometric correction towards red would be acceptable for
terraforming?


I have no idea.

--
Erik Max Francis / / http://www.alcyone.com/max/
__ San Jose, CA, USA / 37 20 N 121 53 W / &tSftDotIotE
/ \ Listen to my song
\__/ Chante Moore
Lsystem / http://www.alcyone.com/pyos/lsystem/
A Lindenmayer systems explorer in Python.


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