Zodiacal Light in May Astronomy


Stan Blank wrote:

Hi Dr. Bri,

While catching up on my reading (woefully behind… too many interests and not enough lifetimes!) I noticed on page 20 of the May Astronomy magazine that the author (Stephen James O’Meara) mentions seeing what he thought might be the Zodiacal light near the end of a solar eclipse. He mentioned that the Zodiacal light was essentially from the comet dust and the collision of asteroids.

When (and if) time permits, isn’t the dust also from planetary formation?

All the best,


Brian replied:

HMM … !! I very much doubt if the ZL could be seen at any part of a total solar eclipse. My experience of even GOOD eclipses in clear skies was that you could see planets, and 1st magnitude stars at a pinch, and not much more !

The origin of the Zodiacal Dust is mainly as he says though, as far as we know – cometary debris and results of collisions in asteroid families … plus a small component of interstellar dust drifting through … which I thought I had discovered in 1971 !

Debris from the days of formation of the planets would long since have spiralled into the Sun because of the Poynting-Robertson effect … which is the result of solar radiation slowing down the particles by a tiny amount due to their orbital speed … a bit like the effect of rain slowing us down when we run (does it ??! )



Stan replied:

Ah… interesting and it sounds like he should have given you due citation! The interstellar dust component is fascinating and would lead to other questions such as is empty space really empty? (quantum virtual particles aside)

I had not heard of the Poynting-Robertson effect, but it does make sense. Now I have something else to research!

Age has slowed my running to the point where I can use a sundial rather than a stopwatch, but your analogy is excellent… and I agree that even if not measurable, rain would have to slow us down unless we can compensate for the collision energy. As a thought experiment (an Einstein gedanken experiment?), you could imagine increasing the intensity of the rain until it becomes a solid flow of water, which would definitely cause a change in your motion! As slow as I run, I should just stay inside when it rains (or even if it is windy) or I’ll never get anywhere… 🙂

Thanks… this old physics teacher still enjoys learning!


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