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22 votes

Can one see a black hole?

I think, that's a bit semantics, and a question of what do you call 'I see something': If you see the shadow cast by an object on a bright background - do you see the object? Do you see Mercury or ...
planetmaker's user avatar
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12 votes

Can one see a black hole?

No, you cannot "see" a black hole, only the way that it interacts with objects or light in its vicinity. In terms of interacting with other objects, the classic observations that betray the presence ...
ProfRob's user avatar
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8 votes
Accepted

Why does the solar wind switch to flowing straight by the time it reaches Earth?

When plasma moves in a magnetic field then the charged particles follow helical paths around the field lines, due to the $q\vec{v}\times \vec{B}$ Lorentz force. If the radius of gyration is small, ...
ProfRob's user avatar
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7 votes

Density of Plasma in Solar Corona

It depends on which region you consider. The lower corona has a plasma number density of the order of $10^9 cm^{-3}$, the upper corona about $10^5 cm^{-3}$. This is all quite variable though, ...
Thomas's user avatar
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6 votes

Can one see a black hole?

Yes, we can, indeed, "see" a black hole and we just did not too long ago. You see, being able to "see" an object is not solely about "reflection" alone: rather, you "see" things by them interacting ...
The_Sympathizer's user avatar
5 votes

Can one see a black hole?

This article explains what the image shows. This distinct structure is a result of the warped spacetime around massive objects like black holes. The ring of light is comprised of photons from the ...
Steve Linton's user avatar
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3 votes

Why is solar corona in visible light filamentary?

The coronal plasma is not spatially homogeneous. It preferentially exists inside heated magnetic structures, which take the form of filamentary loops. It is better to imagine these structures as ...
ProfRob's user avatar
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3 votes
Accepted

The Sun's Alfvén critical surface; what was known about its existence and location before Parker Solar Probe "touched the Sun"?

I'm not sure this question is a meaningful one to ask because the "existence" of the Alfvén critical surface is implied by the very definition of it, which is a man-made construct. My answer ...
zephyr's user avatar
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2 votes

Physical properties of the stellar corona?

...how typical is the solar corona? The Sun is remarkably "average" (e.g., see https://physics.stackexchange.com/a/262732/59023). So my best guess is that the corona is also remarkably &...
honeste_vivere's user avatar
2 votes

How could the polarizer in early coronagraphs make the Sun's corona more visible against the daytime sky?

When you look at the Sun in white (visible) light, what you see is actually sunlight that has scattered from free electrons in the solar corona. This is known as "Thomson scattering". If we view the ...
ProfRob's user avatar
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2 votes

Would the solar corona be visible from the distance of the outer planets?

When the sun is about to rise for a given location is disk or photosphere is totally covered by the planet. The situation is similar to that of a total eclipse but we can't see the corona rising first ...
Alchimista's user avatar
2 votes
Accepted

Would the solar corona be visible from the distance of the outer planets?

If the sun is ever perfectly eclipsed as it is on Earth, then yes, the corona would be visible. The only reason we can't usually see the corona is because it is way dimmer than the rest of the sun. If ...
Pika Supports Ukraine's user avatar

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