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EckJerome
2002-Jan-11, 11:29 PM
Ah, here is a ubiquitous piece of Bad Astronomy:

From "Eye Safety And Solar Eclipses" linked to at http://www.williams.edu/Astronomy/IAU_eclipses/


The only time that the Sun can be viewed safely with the naked eye is during a total eclipse...


Excuse me? The sun is not visible during totality, it is blocked by the moon. There is NEVER a time that the sun can be viewed safely with the naked eye.

Sometimes it is correctly stated that the only time to safely view an "eclipse" (of the solar variety) is during totality.

Eric

MongotheGreat
2002-Jan-12, 01:11 AM
On 2002-01-11 18:29, EckJerome wrote:
Ah, here is a ubiquitous piece of Bad Astronomy:

From "Eye Safety And Solar Eclipses" linked to at http://www.williams.edu/Astronomy/IAU_eclipses/


The only time that the Sun can be viewed safely with the naked eye is during a total eclipse...


Excuse me? The sun is not visible during totality, it is blocked by the moon. There is NEVER a time that the sun can be viewed safely with the naked eye.

Sometimes it is correctly stated that the only time to safely view an "eclipse" (of the solar variety) is during totality.

Eric


Isn't the corona a part of the sun? So the sun can be seen during totality. But not the whole sun. But then the corona can only be seen during totality. So maybe the corona is the only part of the sun that is safe to look at.

EckJerome
2002-Jan-14, 03:35 PM
Isn't the corona a part of the sun?


Is it? My textbook understanding is that the corona is plasma resulting from the sun's intense magnetic field.

I'm not sure, but I would pose that the corona is not a part of the sun itself. That would be akin to saying that Earth's van Allen Belts are a part of Earth itself. Could you say you had seen the "Earth" if you only see the van Allen Belts?

Food for thought. Maybe my analogy is off.

Eric

Silas
2002-Jan-15, 11:28 PM
It's fodder for nitpickers: the Corona is as much "part" of the sun as the tail of a comet is "part" of the comet. Yes? No? More a matter of law than of science, e.g., it depends on how you want to define it.

(Are the very highest layers of the earth's atmosphere "part of the earth?")

Silas

MongotheGreat
2002-Jan-16, 01:27 AM
My textbook understanding is that the corona is plasma resulting from the sun's intense magnetic field.


According to what I learned in my general astronomy course, the corona is part of the sun. While the sun's "surface" is the photosphere, the corona is still part of the stellar atmosphere. There is no strict defining line between the photsphere and the less dense parts of the sun (the corona), that is, there is a general decline in pressure.

Mongo

DStahl
2002-Jan-16, 06:41 AM
Mongo, would that stand up in real estate court?

Sorry, it's late and I'm a bit giddy. Here's a serious question: Does the corona rotate in lockstep with the photosphere? (I'd assume that the Sun's magnetic field would cause it to, but, er, I am sometimes wrong.)

--Don, yes, not DoctorDon

MongotheGreat
2002-Jan-16, 06:55 AM
Well, that sure is a good question, one that I don't know the answer to. I would think that it wouldn't, at least not "In lockstep" with the photosphere. That would mean that particles at the edge of the corona would have to have the same angular velocity as on the photosphere.
I'm just not sure about what, if any, structure the corona has. I am going to try to look into this though.

Dr. Mongo (how's that sound?)

GrapesOfWrath
2002-Jan-16, 09:38 AM
The photosphere doesn't even rotate in lockstep, does it?

So, do you mean, is the patch of corona just above a particular patch of photosphere moving in approximately the same direction? It'd pretty much have to, depending on how you described "approximately". There'd be a corliolis effect of course.

Kaptain K
2002-Jan-16, 10:31 AM
No part of the Sun rotates in lockstep. The core rotates about once a week. The photosphere rotates about once every 28 days at the equator, every 35 days at the poles.

DStahl
2002-Jan-16, 08:04 PM
Hey, Captain my Captain, I thought I had read something describing all sorts of rotational complications in the layers of the Sun.

Is the corona part of the sun? Heck, if the photosphere doesn't even rotate at the same rate as the core, is it part of the sun? I once played devil's advocate in a field botany class, noting that the supposedly seperate species Iris tenax and Iris chrysophylla interbreed in parts of their range and therefore are not really seperate species. The professor impatiently corrected me: these distinctions are human constructs imposed on the natural world and do not, in many cases, correspond to a cut-and-dried separation of phenomena. Nature abhors classification.

(Best teacher I ever had, bar none. If you attended his class and didn't learn it sure as heck wasn't because he hadn't given you every opportunity.)

--Don

<font size=-1>[ This Message was edited by: DStahl on 2002-01-16 15:06 ]</font>

SeanF
2002-Jan-16, 09:03 PM
On 2002-01-16 15:04, DStahl wrote:

I once played devil's advocate in a field botany class, noting that the supposedly seperate species Iris tenax and Iris chrysophylla interbreed in parts of their range and therefore are not really seperate species. The professor impatiently corrected me: these distinctions are human constructs imposed on the natural world and do not, in many cases, correspond to a cut-and-dried separation of phenomena. Nature abhors classification.



Well, now, wait a second. Shouldn't your professor simply have said that different species which are closely enough related can interbreed -- that the ability to interbreed is not a deciding factor in the definition of "species"? The general admonition on distinctions quoted above sounds an awful lot like "They're different species if we/I/the PTB say they're different species, and they're not if we say they're not."

GrapesOfWrath
2002-Jan-16, 09:34 PM
Careful, there, Don, the Earth's core doesn't rotate at the same rate as the mantle, apparently. And we know that the atmosphere moves around a lot.