Astronomy Picture of the Day 5-08-02

NASA ^ | 5-08-02 | Robert Nemiroff and Jerry Bonnell

[petuniasevan]

Like honeybees, for instance.
Here's a chart of wavelength sensitivity for human vision and bee vision.

This is a comparison of wavelengths visible to humans and bees.
The range of vision for the bee and butterfly extends into the ultraviolet.
The petals of the flowers they pollinate have special ultraviolet patterns
which guide the insects deep into the flower.

This doesn't contradict my earlier assertion that UV imaging must be done from orbit; obviously a little UV gets through. It's what gives you a tan (or sunburn). It's just that 99% of "soft" UV is blocked, and higher-energy "hard" UV is 100% blocked, as are X-Rays.

[petuniasevan]

Daylilies in normal daylight visible spectrum.

Same daylilies in UV light.

Although we can't be sure exactly HOW UV light appears to bees, it seems that the UV image above shows dark central regions in the flowers which guide the bee to the nectar.

[petuniasevan]

Ordinary yellow weedy dandelions become rare jewels in UV light.

[Helix]

Beautiful pictures and a damned good point! That'll teach me to be less vague in my musings! My old bio professors would kill me if they knew I had (lazily) suggested insects didn't ever use UV.

To be honest, I had wandered off track and into a supposition about the stable atmosphere we enjoy today.

I vaguely remembered reading about a theory of Fred Hoyle's on the ability of Drosophila (I think) to see the very short (980 A)wavelengths of UV which, according to him, could never have penetrated the atmosphere during the time that insects have been present on Earth. Therefore, he believed they were under no selective pressure to develop such an ability. He also thought the insects could not have survived the light's mutagenic effects.

These assertions always seemed a little over-the-top to me since we've witnessed how much the atmosphere can change in just the few years scientists been studying it. The constant change of the "hole" in the ozone, for example. And although UV light is a mutagen, all organisms have some ability to repair the damage. It seems possible that, at one time, shorter UV rays were able to penetrate the atmosphere and the ability to see these wavelengths was used by those insects.