Where Can I Find Candle that Changes Color as it Burns?

Some where in the past I saw a very pretty candle that changes colors as it supposedly burns and I believe it was powered by a battery or something.

I think you are referring to the fake candles that use LED's to mimic a real candle. Here are some links for you to try:

http://www.bluegoosecandlesandmolds.com/index.cfm/fa/items.main/parentcat/12150/subcatid/0/id/325044

http://www.lighting-china-supplier.com/d-p13153498-Candle_with_Multi_Color_Changing_Light/

http://www.epromos.com/product/8825707.html

I couldn't find any references to a multi-color wax candle. It would be a challenge to make because you would have to put additional chemicals in the wax to make the flame different colors. This would be a neat thing for somebody to try and make.

Can staring at a light bulb for periods of one to two minutes at a time cause permanent eye damage?

Incandescent light bulbs are generally safe to look at. I am wondering why would you stare at an incandescent light bulb for such a long time?

One might think that a 50W incandescent light bulb is more dangerous than a 50 mW laser pen (1000 times less power) but power is only one factor to consider. (Also 50W represents the power consumed by the incandescent light bulb, the emitted power is significantly less than that).

The main factor that makes the laser pen MUCH more dangerous is that the light pen emits a collimated beam, all of which could potentially enter the eye, whereas the light bulb emits in all directions. The amount of power that gets into your eye from the light bulb drops off significantly with the square of the distance from the bulb (if you move twice as far away, the power drops by a factor of 4).

Another factor to consider is the size the the image on your retina. A lightbulb is an "extended source" whereas the laser pen is a "point source". This means that the size of the image spot on the retina will be larger for a lightbulb, and the energy density will be less, reducing the risk of injury.

Also, don't stare at the sun! Staring at the sun is dangerous.

Is this caterpillar poisonous to pets?

Hello Science Brian, I just wanted to know if this is a caterpillar, because I find these in my backyard and my dogs might want to eat them. Are they poisonous if eaten by a pet?





What a nice picture!

I am not an expert in caterpillars, so I had to ask for help with this one. (Thanks Dave!) This is a Tobacco Hornworm (manduca sexta). I thought it was a tomato hornworm, but what do I know? They are often confused. Like most caterpillars, it's main job is to eat! Tobacco hornworms feed on tomato, tobacco and Jimson weed leaves.

My expert friend says that your dogs probably won't have much interest in eating these because they can taste bad. I didn't ask him how he knew that. The hornworm can get your pets sick, if it has been eating a toxic plant like Jimson weed (also known as stink weed). However, most likely your dog would spit it out before swallowing it because of the bad tasted.

What Causes Hemophilia?

Hemophilia is a rare inherited blood disorder. This genetic disease is caused by a defect in the genes that determine how the body makes blood clotting factors. Because these genes are on the X chromosome (men have XY women have XX), women can be carriers of the disease (if they have one defective X chromosome) whereas men with the defective gene will have hemophilia.

Why Isn't Black a Color?

Color is based on human perception of the visual spectrum of light. Our ability to see different colors is due having a variety of cone cells on the retina that are sensitive to different wavelengths of light.

Black is the label we give to the perception of the absence of light reaching the eye. Objects that absorb all wavelengths of light, rather than reflect them, appear black. We also see black (or darkness) at night or when we shut off the lights.

When somebody says "black is not a color" they are referring to the fact that black is not a scientific observation of light. However, since color science is based on human perception, and our eyes perceive the absence of light, it is OK to call black a color.

Why Are Candles Made of Wax?

Well, one might argue that by definition we call a light source made of wax a "candle" (as opposed to an oil lamp or match which has a similar purpose but uses different materials).

But what is special about the wax in a candle?

To understand the mechanisms of how a wax candle burns, read Why doesn't candle wax burn without a wick? first.

Wax has several unique properties that make it an ideal material to be used as the "fuel" of a candle. It is solid at room temperature, which makes it easier to handle than liquid lamp oil which must be kept in a container. It is also malleable and melts at a low temperature, making it easy to shape into whatever form you want it to be. The low melting point is very important because the energy required to melt the wax must be less than what is generated burning it, or the flame would not be self-sustaining. Natural sources of waxes (such as beeswax and paraffin) are commonly available for use in candles.

Why doesn't candle wax burn without a wick?

The wick is the most important part of a candle! The mechanics of a burning candle are actually quite interesting. The wax, in it's solid form, does not burn. When you bring the flame of a match near the wick, the wax directly below starts to melt due to the heat (or in some cases, the actual wick material will start to burn and then heat up the wax below). The melted liquid wax is then drawn up to the flame on the wick through capilary action. As the liquid wax is drawn up into the flame, it is heated until it vaporizes. Once it is in gaseous form, it is ignited by the flame. The combustion of the gaseous wax keeps the flame going and generates enough heat to warm up some more wax. The cycle continues as the candle wax is burned away. Nifty!