Why is the jet exiting the tube shown in the figure visible, although water vapor is invisible?

It is a fog made up of tiny water droplets. Water vapor is invisible. The difference between the jet temperature and the ambient temperature is large. Therefore, it begins to condense and turn into microscopic droplets that are no longer gas, and are visible to the eye. Moisture begins to freeze on the fly, which is why it seems to us that we see steam. And the lower the ambient temperature, the more such water vapor will be.

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