Can a Gamma Ray Burst create a shadow on Earth from the Sun?

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Discussion Overview

The discussion revolves around the hypothetical scenario of whether a Gamma Ray Burst (GRB) could cause the Sun to cast a shadow on Earth if the GRB were positioned behind the Sun. Participants explore the implications of GRBs and supernovae in terms of their brightness and potential to create a shadow on Earth, considering both theoretical and observational aspects.

Discussion Character

  • Exploratory
  • Debate/contested
  • Technical explanation

Main Points Raised

  • Some participants propose that the shadow cast by the Sun would be approximately the size of the Sun itself.
  • Others question the actual size of the shadow on Earth, considering the apparent size of the Sun and the distance to Earth.
  • It is suggested that the Sun acts as an efficient gamma ray shield, and its movement across the sky affects how long it could shield Earth from a GRB.
  • Some participants argue that GRBs are not very bright in the visible spectrum, implying that any shadow created would not be significant.
  • There is a discussion about the relative brightness of supernovae compared to the Sun, with some stating that supernovae would not outshine the Sun in visible light.
  • One participant expresses uncertainty about how the glare from a GRB or supernova would affect the visibility of the Sun and whether it would cast a shadow.
  • Another participant clarifies that the angular diameter of the Sun does not translate directly into a shadow size on Earth, emphasizing that all of Earth would be in "shadow" if a sufficiently bright source were present.
  • Some participants note that even if a supernova were to occur, it would need to be extremely close to match the brightness of the Sun.
  • There is a mention of the transition region rather than a distinct shadow due to the Sun's lack of a solid surface.

Areas of Agreement / Disagreement

Participants express differing views on the potential for a GRB or supernova to cast a shadow on Earth, with no consensus reached on the significance of such a shadow or the conditions under which it might occur.

Contextual Notes

The discussion includes assumptions about the brightness of GRBs and supernovae, the distances involved, and the nature of shadows cast by non-solid sources like the Sun. These factors remain unresolved and are critical to the arguments presented.

tionis
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Would a nearby Gamma Ray Burst (GRB) cause the Sun to cast a shadow on Earth if it were to shine from behind it?
 
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What would you expect for the size of this shadow?
 
Hi, Ultra. I guess the shadow would be the size of the Sun, right?
 
To a very good approximation, indeed.
What do you know about the relative size of sun and earth?
 
Yes, but what size is the shadow of the sun on the surface of the earth?
 
As a plasma ball, the sun is a very efficient gamma ray shield. The sun moves across the sky an apparent 60 arc minutes per day. It's apparent diameter is about 30 arc minutes. You should be able to figure out from this about how long the sun could shield us from a GRB [a point source] occurring on a line of sight behind the sun.
 
mfb said:
To a very good approximation, indeed.
What do you know about the relative size of sun and earth?

The Sun is bigger but farther, and Chronos said it is 30 arc minutes in diameter.

UltrafastPED said:
Yes, but what size is the shadow of the sun on the surface of the earth?

30 arc minutes?

Chronos said:
As a plasma ball, the sun is a very efficient gamma ray shield. The sun moves across the sky an apparent 60 arc minutes per day. It's apparent diameter is about 30 arc minutes. You should be able to figure out from this about how long the sun could shield us from a GRB [a point source] occurring on a line of sight behind the sun.

Ok. So what I basically want to know is if the visible luminosity of a GRB is powerful enough to cause the Sun to cast a shadow on Earth. I use GRBs as an example, but I guess a supernova could do it, too, right?
 
tionis said:
The Sun is bigger but farther, and Chronos said it is 30 arc minutes in diameter.

30 arc minutes?
How big is the Earth in arc minutes? How much of the Earth does that cover...?
Ok. So what I basically want to know is if the visible luminosity of a GRB is powerful enough to cause the Sun to cast a shadow on Earth.
Gamma ray bursts aren't very bright visibly. So it wouldn't be much of a "shadow"
I guess a supernova could do it, too, right
Yes, and much brighter than a GRB. But still not much of a "shadow".
 
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russ_watters said:
How big is the Earth in arc minutes? How much of the Earth does that cover...?

I don't know..:redface:

I'm trying to picture what the sky would look like if the Sun were to 'eclipse' a GRB or a supernova. It seems that the glare from either of those two events could overwhelm the visible brightness of the Sun by several orders of magnitude, no?

Are you saying the Sun wouldn't cast any shadow on the Earth with that much light in the background?
 
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  • #10
Radiation from a GRB behind the sun would be enormously diminished.
 
  • #11
tionis said:
I don't know..:redface:
It's a trick question; That doesn't translate into a size on earth. For this situation, the angular diameter of the sun doesn't matter, only the fact that its real diameter is much larger than earth. All of Earth will be in "shadow"
I'm trying to picture what the sky would look like if the Sun were to 'eclipse' a GRB or a supernova. It seems that the glare from either of those two events could overwhelm the visible brightness of the Sun by several orders of magnitude, no?
No. Those events are nowhere close to as bright as the sun (er - perhaps a GRB from within our galaxy would be, but they are rare events and so far are only seen from far away). It depends on distance of course, but a supernova in our galaxy might shine as brightly as Venus.
Are you saying the Sun wouldn't cast any shadow on the Earth with that much light in the background?
Not in the normal sense of the word, no.
[edit] Tionis, I apologize; I accidentally edited your post instead of replying (for moderators, the buttons are right next to each other). I've tried to restore it to its original form.
 
  • #12
Supernovae are bright, but they won't outshine the sun in visible light. The supernova of 1604 was at a distance of 20 000 light years and reached an apparent magnitude of -2.5. Our sun is 10^10 times brighter than that, in order to get the same magnitude a similar supernova would have to be closer by a factor of 100 000, or .2 light years away. There is no star in this distance, and I think all the stars within 10 light years won't explode as supernova.

Even if there would be some very bright source, the sun has no solid surface. There would be no shadow similar to a cloud, there would be some large (relative to clouds) transition region.
 
  • #13
OK. I'm convinced. Thanks :-)
 

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