# B Question on solar eclipse

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1. Jul 11, 2016

### parshyaa

during solar eclipse , moon's shadow on earth is almost a point [267 km which is a 0.00000523 % of earth's surface area] which means that sun light must bend, if it is not bending then we would never get a point shadow of moon on earth. now the question arises why sun light bends, is it a question of relativity( if yes then don't explain why it bends, i will try it myself)

2. Jul 11, 2016

### Staff: Mentor

Have you calculated what the width of the Moon's shadow on Earth would be given the size of the Sun, the size of the Moon, and the distances of both bodies from the Earth, assuming that light travels in straight lines? If you haven't, I suggest you do so.

3. Jul 11, 2016

### parshyaa

i have calculated the distance of moon sun and their diameters through aristarchus method. but i want to know wether bending of light is a question of relativity or not.

4. Jul 11, 2016

### Orodruin

Staff Emeritus
You are simply wrong. There is no need for the light to bend. The Sun is much bigger than the Moon.

5. Jul 11, 2016

### Ibix

@parshyaa - Gravitational lensing, which is what I think you are talking about, is a feature of relativity, yes. It is not relevant to solar eclipses because the moon does not produce any significant lensing.

Eddington studied lensing by the Sun during a total eclipse, but the eclipse was basically used to blot out the Sun so that stars could be seen near it. In a sense, the moon was part of the detector apparatus, not part of the gravitational field being studied.

6. Jul 11, 2016

### parshyaa

Okkk, sun is bigger then moon and earth , then why shadow of moon during solar eclipse is too small , why it is not bigger as compared to the source(sun) . For getting a smallèr shadow light must bend. Please correct me if i am wrong

7. Jul 11, 2016

### Ibix

You are wrong. The larger the source the smaller the zone of totality ("umbra"), all other things being equal. Draw it out. You only need a pencil and a straight edge.

8. Jul 11, 2016

### parshyaa

Basically you are saying that bigger the source smaller will be the umbra (shadow).

9. Jul 11, 2016

### Ibix

Yes. The penumbra (where you will see a partial shadow) will be larger, but the umbra will be smaller or may be non-existent. In astronomical terms that latter case is called a transit.

10. Jul 11, 2016

### parshyaa

But I am not able to do it experimentally, could you suggest a good way to observe this phenomenon

11. Jul 11, 2016

### Orodruin

Staff Emeritus
Take a big light source and a small object. Observe how the shadow of the object depends on the distance to the surface the shadow falls on. A room with a single window and only ambient light (no direct sunlight) will do. Note how the shadow is the same size as the object when the object is just next to the surface but becomes fuzzy as you move the object closer to the source.

12. Jul 11, 2016

### Ibix

Redraw the diagrams here https://en.m.wikipedia.org/wiki/Umbra,_penumbra_and_antumbra using a pencil and straight edge. Vary the source size but not its position and see what happens. Or use a cardboard circle as the moon and a light bulb for the source. Cut different sized holes in a piece of card to make different sized sources. Careful measurement would be needed - the drawing method is easier.

None of this is relativity, and it's all easily Googleable.

Edit: beaten to it by Orodruin, I see.

13. Jul 11, 2016

### parshyaa

i know that if i move a object to the source the shadow will become larger and if i move object away from it, shadow will become smaller, i want to know why this happens. i think this will only be possible when light will bend. without bending shadow will not be smaller.

14. Jul 11, 2016

### Orodruin

Staff Emeritus
No, I suggest you do the ray diagram instead of just repeating the same misinformation.

The shadow (umbra) does not become larger when you move the object towards the source. What becomes larger is the penumbra where the source is partially obstructed. This results in a fuzzy shadow. I suggest you actually tead the wiki page linked earlier.

15. Jul 11, 2016

### parshyaa

okkk

16. Jul 11, 2016

### parshyaa

thanks a lot orodruin and lbix, i got it and sorry for taking a lot of time