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Peter B
2001-Oct-29, 04:43 AM
I'm in the process of writing a short story, and one of the relevant points I'd like to get right is the classification of a star.

Now, if I remember it right, the sequence goes something like W, O, B, A, F, G, K, M, N. And our Sun is a G, with a lifespan of about 10 billion years, yes?

What I'd like to know is the classification for a star which would have a lifespan of about 1 billion years. Also, how big would such a star be, how bright and what colour?Also, how far from it would an Earth-like planet have to orbit, roughly?

Nick
2001-Oct-29, 09:00 AM
Here's a quick link:

http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml

It does state life span, though.

Nick /phpBB/images/smiles/icon_smile.gif

Kaptain K
2001-Oct-29, 09:50 AM
A star with a billion year life span would be somewhere in the F range.

The habitable range would be on the order of 2.5 AU (the distance of the inner asteroids).

These numbers are very approximate and are subject to correction by those here who know more about this than I, but they should be in the "ballpark".

Hat Monster
2001-Oct-29, 10:18 AM
A star with a life time of around a billion years would be extremely similar to Sirius, which is an A2. Life would be impossible around such a star, the proper distance would be about 3AU but the hard UV radiation would be intense because brighter stars give off far more UV than they do visible.
I don't think it's possible to have life around anything that isn't F, G or K.

David Simmons
2001-Oct-29, 12:49 PM
On 2001-10-29 05:18, Hat Monster wrote:

I don't think it's possible to have life around anything that isn't F, G or K.



Possibly. But it is not a good idea to underestimate the ablility of life, in some form or other, to evolve in pretty unusual (by our standards) circumstances.

CJSF
2001-Oct-29, 02:02 PM
On 2001-10-29 05:18, Hat Monster wrote:
A star with a life time of around a billion years would be extremely similar to Sirius, which is an A2. Life would be impossible around such a star, the proper distance would be about 3AU but the hard UV radiation would be intense because brighter stars give off far more UV than they do visible.
I don't think it's possible to have life around anything that isn't F, G or K.



EARTH life would be impossible.. but who's to say if said fictional planet wouldn't have some way of blocking the UV, like a super ozone layer or some other mechanism? Maybe the native biota have some UV blocking exoskeletons or other means of blocking or even USING the UV?

Perhaps the planet is rich in some resouce, so it is inhabited, but everyone lives in sheilded dwellings and such. This is for a short story after all.

CJSF

<font size=-1>[ This Message was edited by: Christopher Ferro on 2001-10-29 09:05 ]</font>

Mnemonia
2001-Oct-29, 03:28 PM
Life would be impossible around such a star, the proper distance would be about 3AU but the hard UV radiation would be intense because brighter stars give off far more UV than they do visible.
I don't think it's possible to have life around anything that isn't F, G or K.


Our own Sun gives off more than enough UV to kill us. We just happen to live on a world with an atmosphere that blocks most of it.

Peter B
2001-Oct-30, 12:44 AM
Folks

Thanks for your help, everyone.

Now to stretch the friendship (and the topic).

Imagine early Earth, when life first emerged. What would a visitor see - what colour would the rocks be? What gases would the atmosphere contain? Would there be a blue sky (other colour maybe?), or would there be cloud everywhere? What would the temperature be on the surface?

Again, rough answers are fine - this is all for a work of fiction.

Russ
2001-Oct-30, 01:35 PM
On 2001-10-29 19:44, Peter B wrote:
Folks

Thanks for your help, everyone.

Now to stretch the friendship (and the topic).

Imagine early Earth, when life first emerged. What would a visitor see - what colour would the rocks be? What gases would the atmosphere contain? Would there be a blue sky (other colour maybe?), or would there be cloud everywhere? What would the temperature be on the surface?

Again, rough answers are fine - this is all for a work of fiction.


I'll take a stab at this one. Starting about 650 million years ago, there were single celled biota called prokaryots (pro car e oats) that are called "blue/green algae". For about 150 million years they grew in the oceans and on rocks and tide pools on the shore. If I remember correctly the atmosphere was mostly amonia and CO2.

During that time the sea and sky would look pretty much as they do now. The dry land would have been bare rock as in an open pit mine or rock quarry. Tempuratures would be, roughly speaking, on the hotter side of what they are today.

This may be wrong in the details but correct in the generalities. Anybody have a better response.

Mnemonia
2001-Oct-30, 02:06 PM
On 2001-10-30 08:35, Russ wrote:
I'll take a stab at this one. Starting about 650 million years ago, there were single celled biota called prokaryots (pro car e oats) that are called "blue/green algae". For about 150 million years they grew in the oceans and on rocks and tide pools on the shore. If I remember correctly the atmosphere was mostly amonia and CO2.

During that time the sea and sky would look pretty much as they do now. The dry land would have been bare rock as in an open pit mine or rock quarry. Tempuratures would be, roughly speaking, on the hotter side of what they are today.

This may be wrong in the details but correct in the generalities. Anybody have a better response.


I'm not so sure about the CO2 as recent as 650 million years ago. Most of the Earth's CO2 is locked up in carbonate rocks and the oceans, which formed a long time before 650 million years ago. The amtosphere was probably mostly Nitrogen, with significant amounts of Water vapor, and traces of oxygen, C02, argon, and the other trace elements we have today (with exception to CO /phpBB/images/smiles/icon_frown.gif ).

It was more than likely much like our atmosphere today, without most of the O2 and CO, and since both of those are colorless, the atmosphere likely looked blue (from the ground!) then, too. Cloud cover was probably about the same as well, but varies depending on whether the Earth is in an ice age or not at that time. I doubt Earth would have been totally cloudy or cloudless, but the case could be made that a quarter or 4 times as many clouds have existed at some time in the past.

There would have been less of a greenhouse effect though without life pumping fresh CO2 into the atmophsere - so the Earth as a whole would have been colder, not hotter.

The Earth rotated faster and the moon was both closer and revolved more quickly back then though. So daytime and nighttime came more often. I seem to remember reading Earth had something like 480 16-hour days to a year long ago, but that estimate may not be correct for 650 million years ago.

Bob
2001-Oct-30, 03:35 PM
http://www.ucmp.berkeley.edu/precambrian/archaean.html

The earliest fossilized evidence for single celled bacteria is dated back 3.5B years, amazingly soon after the formation of the Earth about 4.5B years. As noted in the link, the atmosphere then was probably methane, ammonia, and other unpleasant stuff.

Nick
2001-Oct-30, 05:07 PM
You all realise, folks, that we have just all become 'unpaid' authors of a sci-fi book!!!

Nick /phpBB/images/smiles/icon_wink.gif

<font size=-1>[ This Message was edited by: Nick on 2001-10-30 12:08 ]</font>

Kaptain K
2001-Oct-30, 06:22 PM
Not authors, technical consultants. /phpBB/images/smiles/icon_wink.gif

Peter B
2001-Oct-31, 12:11 AM
Nick accurately observed that you've all become unpaid authors.

Congratulations! /phpBB/images/smiles/icon_smile.gif

You'll earn as much from the exercise as I will. /phpBB/images/smiles/icon_wink.gif

Seriously, though, in the first billion years or so of the Earth's history, can we be reasonably certain that the Earth's atmosphere was methane and ammonia, or was it nitrogen and water vapour?

Simon
2001-Nov-01, 08:05 PM
Do we get our names in the Aknowledgements? /phpBB/images/smiles/icon_biggrin.gif

Erm, I don't know a whole lot about it, but nitrogen and water vapor seems much more likely to me. Nitrogen is very chemically inert, so if you have some there it stays there. And you get water vapor just by having water. You might have a fair bit of CO2 though -the earth was very volcanically active then, wasn't it? Might have some traces of methane, but I doubt that there'll be much.

jkmccrann
2005-Nov-15, 02:54 PM
I'm in the process of writing a short story, and one of the relevant points I'd like to get right is the classification of a star.

Now, if I remember it right, the sequence goes something like W, O, B, A, F, G, K, M, N. And our Sun is a G, with a lifespan of about 10 billion years, yes?

What I'd like to know is the classification for a star which would have a lifespan of about 1 billion years. Also, how big would such a star be, how bright and what colour?Also, how far from it would an Earth-like planet have to orbit, roughly?

I'm interested to know if this project ever got off the ground Peter B? Can you share the fruits of your creativity?

:)

trinitree88
2005-Nov-15, 03:37 PM
I think the earliest photosensitive pigments were in brown algae, followed by red, then the blue-green. It usually takes a multi-photon process to free an electron in them.The brown used the red end of the spectrum. When the red (anthocyanins) evolved, they used the blue end. The evolution of chlorophyll produced a bioform that competed for available energy over both predecessors spectral needs simultaneously. In green plants,the red end stimulates maturation, and flowering. The blue end stimulates short stocky growth. This allowed green plant life to eventually dominate, and evolve more rapidly. When you walk a weedy saltwater beach you often see some of all three types. Leave it to my Irish ancestors to eat red dulce...yuk. Of course all your chocolate ice cream is loaded with carrageenan...brown algae, here, here! Pete.

tracer
2005-Nov-15, 07:40 PM
Starting about 650 million years ago, there were single celled biota called prokaryots (pro car e oats) that are called "blue/green algae". For about 150 million years they grew in the oceans and on rocks and tide pools on the shore.
Your time scale is a bit off.

The blue-green "algae", more properly called cyanobacteria, appeared on the Earth shortly after life began. (The oldest fossils ever discovered, 3.5 billion years old, are in fact the fossil remains of cyanobacteria.) They were photosynthetic organsims that produced a toxic waste gas called "oxygen", which spelled instant death to any of the many non-aerotolerant life forms it touched.

By about 2.5 billion years ago, the cyanobacteria had become so successful that the oceans had become saturated with oxygen. Non-aerotolerant anaerobes were driven from the open seas and had to find refuge in hidden places where the oxygen could not reach, or perish. (This mass-extinction is known as the "oxygen holocaust." It is the worst case of air pollution in Earth's history.) The oxygen bubbled out of the ocean and into the air, eventually giving us the 20% oxygen atmosphere and the Ozone Layers we know today.

It is important to note that life had no problems thriving in the oceans long before Earth had any ozone layers. Water will also shield out ultraviolet light. (And visible light, too -- ever see those movies they film in the deep oceans? It's totally pitch black all around, except for the submersible's lights and the few bioluminescent critters that scuttle by.)

Vhear
2005-Nov-15, 09:47 PM
Now, if I remember it right, the sequence goes something like W, O, B, A, F, G, K, M, N. And our Sun is a G, with a lifespan of about 10 billion years, yes?

I never heard of the sequence starting with W or ending with N.:eh: No star has been found that is a higher spectral class than O3.

Doesn't the new sequence goes something like this: O,B,A,F,G,K,M,L,T

THE SPECTRAL SEQUENCE
Class
O ionized and neutral helium, weakened hydrogen, bluish, above 31,000 K
B neutral helium, stronger hydrogen, blue-white, 9750-31,000 K
A strong hydrogen, ionized metals, white, 7100-9750 K
F weaker hydrogen, ionized metals, yellowish white, 5950-7100 K
G still weaker hydrogen, ionized and neutral metals, yellowish, 5250-5950 K
K weak hydrogen, neutral metals, orange, 3800-5250 K
M little or no hydrogen, neutral metals, molecules, reddish, 2200-3800 K
L no hydrogen, metallic hydrides, alkalai metals, red-infrared, 1500-2200 K
T methane bands, infrared, 1000 K

Kullat Nunu
2005-Nov-15, 10:56 PM
W stars are Wolf-Rayet stars. They are very massive stars that have blown out their outer envelopes, or they have lost them to their stellar companions. Therefore these stars are very hot. Types N (and R) are no longer used, they're combined to type C carbon stars. There are another type of carbon stars, S stars. S and C are roughly equivalent to types G, K, and M. None of these spectral types belong to the main sequence you described.

Kullat Nunu
2005-Nov-15, 11:04 PM
I'd like to add that there were eukaryotes (organisms with nuclei in their cells) way before 650 Ma, first ones appeared around 2 billion years ago. Modern eukaryotes include all protists, plants, fungi and animals.

tracer
2005-Nov-16, 01:54 AM
I'd like to add that there were eukaryotes (organisms with nuclei in their cells) way before 650 Ma, first ones appeared around 2 billion years ago.
A couple of years ago, I read a surprising article about the discovery of eukaryote fossils dating to before the Oxygen Holocaust.

Before that, I'd always figured it was the O2 Holocaust that drove the evolution of the eukaryotic forms, or at least opened up the environmental niches they needed to thrive. (What with eukaryotes being aerotolerant and all.) Now, though, it looks like the eukaryotes came first, and the O2 Holocaust was just a happy accident that paved the way for their eventual conquest.

wollery
2005-Nov-18, 05:18 PM
I never heard of the sequence starting with W or ending with N.:eh: No star has been found that is a higher spectral class than O3.

Doesn't the new sequence goes something like this: O,B,A,F,G,K,M,L,T

THE SPECTRAL SEQUENCE
Class
O ionized and neutral helium, weakened hydrogen, bluish, above 31,000 K
B neutral helium, stronger hydrogen, blue-white, 9750-31,000 K
A strong hydrogen, ionized metals, white, 7100-9750 K
F weaker hydrogen, ionized metals, yellowish white, 5950-7100 K
G still weaker hydrogen, ionized and neutral metals, yellowish, 5250-5950 K
K weak hydrogen, neutral metals, orange, 3800-5250 K
M little or no hydrogen, neutral metals, molecules, reddish, 2200-3800 K
L no hydrogen, metallic hydrides, alkalai metals, red-infrared, 1500-2200 K
T methane bands, infrared, 1000 K
Just to clarify that point, L and T types are substellar, ie brown dwarfs.