# Pool 'anomaly'?

1. Aug 4, 2015

### Abby4761

I hesitate to say this is an anomaly, as it probably has a simple answer, but I have noticed a line of light moving horizontally across my pool every now and then, it starts at the deep end and moves continuously to the shallow end, moves up the wall at the shallow end, and ends at the surface of the water creating a small ripple effect. This can't be light and I suspected it was heat rising from a deeper to a shallower medium. Any thoughts?
thanks for any input!

2. Aug 4, 2015

### Staff: Mentor

Well is it light or isn't it?

3. Aug 4, 2015

### Staff: Mentor

Welcome to the PF.

Sounds like a small wave that starts from the deep end for some reason. Is there some source like a strainer or something at the deep end that could occasionally start a small wave?

4. Aug 4, 2015

### Staff: Mentor

Your question doesn't give much detail, but I'm guessing that the "line" is a variation of the following kind of reflection.

http://ak.picdn.net/shutterstock/videos/568828/preview/stock-footage-swimming-pool-bottom.jpg [Broken]

In a cosmology course on video, Professor Susskind pointed out the similarities between pool bottoms and the large scale variations in the universe. He then continued to explain the common mathematics of both.

So if my guess it correct, your question relates to very interesting physics.

Last edited by a moderator: May 7, 2017
5. Aug 4, 2015

### Abby4761

No, it comes randomly and in a straight line of light that moves across the pool to the shallow end in about 30 seconds. Thanks for the input!

6. Aug 4, 2015

### DaveC426913

Can you describe in more detail what you mean by straight line? where does it start? Where does it end? Which way is it oriented? How does it move in relation to its orientation? Is there a breeze? Is it sunny? Are there waves? Does the line of light shimmer?

Me, I'm suspecting a surface ripple from a very light gust of wind. It looks exactly like a mosquito buzzing the water.

7. Aug 4, 2015

### Abby4761

It starts in the deep end of the pool which is facing towards the east., and the shallow towards the west. This happened when it was sunny and about 90 degrees. however it has recurred in different temperatures and times of day. The line looks like what anorlunda referred to, but it is straight and sloped (highest point in the northeast and lowest southwest). The pool is about 30 meters long and it takes the line about 45 seconds to reach the shallow end of the pool. When it comes to the end of the shallow end it makes its way up the curved pool wall, effectively shrinking this moving mystery line, and when it reaches the surface the line disappears and creates a small ripple of water.

8. Aug 4, 2015

### Staff: Mentor

That's a long pool. Can you post some pictures of the pool and what-all is in the deep end that might be generating a small wave sometimes?

9. Aug 5, 2015

### DaveC426913

This sounds very much like a singleton surface wave making its way down the length of the pool. Waves traveling the length of the pool will last much longer than waves traveling the width.

The light is a hotspot on the pool bottom, caused by the curve of the wave acting like a magnifying glass.

I would have thought though, that you'd see the line reflect back toward the deep end - though I can think of a few reasons why it might not be fully reflective in the shallow end.

Last edited: Aug 5, 2015