Science Questions

Why do I see two reflections?

Sun, 10th Apr 2011

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Phil Arbez asked:

Hello Chris. Really like the show! My question. When I look closely in the mirror I notice that my reflection has a transparent reflection surrounding my own.Best way to accomplish this is to hold your hand up at the bathroom mirror and observe in close proximity,your hands reflection in the mirror. I don't understandwhy there is a transparent reflection outliningthe reflection of my hand.I thought maybe this wasbecause of stereo vision but then whenI closed one eye itis still visible?What is this reflection?


Phil Arbez


Manitoba, Canada


Dave -   This probably means that you're using a standard back-silvered mirror.  So, a normal mirror is made up of a sheet of glass and then they deposit aluminium onto the back of it, which is shiny.  So the main reflection you see is from the layer of aluminium at the back of the mirror.  But the front of a sheet of glass also has a weak reflection.  If you look at any window, especially if its darker on the other side, you will see a reflection of yourself in that.  And so, there will be a second reflection there.  Because of the thickness of the glass, it won't be in exactly the same place, so there are two reflections, the main one from the silvering at the back, and a front one from the sheet of glass in the front.

Chris -   I think the other place where you see this manifest is if you had one of those car rear-view mirrors that you can flick down to stop the person whos got very bright headlights behind from dazzling you at night time.  You flick the mirror down and bizarrely, although the mirror is now pointing downwards and out of your line of view, you can still see an impression of the headlights of the car behind in that mirror - and that will be that reflection off of the glass surface rather than the silver one.

Dave -   They actually put a second piece of glass at a different angle, so then you're seeing the reflection in the glass, not in the mirror itself.


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