# Homework Help: Haloes or rings round the moon?

1. Feb 22, 2016

Why sometimes rings are observed round the moon or sun?
My book says
When the moon or sun is observed through a thin layer of high clouds,reflection of light from fine icy crystals,present in the clouds,results in the formation of rings.
Can someone please elaborate on that so that I can understand easily by using an example or by other means?

2. Feb 22, 2016

### Simon Bridge

3. Feb 23, 2016

Well my trouble in understanding is that how can the reflection of light by the clouds be the reason for formation of haloes?

4. Feb 23, 2016

### Simon Bridge

5. Feb 23, 2016

And why are rainbows bow shaped?

6. Feb 23, 2016

### Simon Bridge

Try looking it up - you'll find that easier to understand because the process is simpler.
Rain comes in spherical droplets - which is why you get the rainbow in that particular shape, and why you have to have your back to the Sun to see one.
Ice crystals come in a range of shapes so the haloes vary in shape and size and position.

7. Feb 23, 2016

Well,I do know it is because of the phenomenon of dispersion that rainbow formation occurs.But I have never thought about how rainbows could be bow shaped.I can't find a logical reason behind why rainbows have to be similar in the shape of droplets.I thought droplets helped in acting like prisms!
And here how does the ring formed due to refraction of light be compared to rainbow formation?

8. Feb 23, 2016

### haruspex

You need to separate two principles. The separation of colours in a rainbow is indeed due to dispersion, but even if the light from the sun were all one wavelength there would still be monochromatic rainbows. The bow itself is due to internal reflection.
For a ray of light from the sun to be reflected inside a raindrop to reach your eye, your eye and the sun must subtend a particular angle at the raindrop. What is the locus of the raindrops at that angle?