Problem of the Week

Chapter 18: Refraction and Lenses

Problem of the Week

SOHO and EQUI-NO

This Problem of the Week is on two separate phenomena, both related to the sun. The first is about the Solar and Heliospheric Observatory, SOHO, which is a two-ton spacecraft devoted to looking at the sun 24 hours a day. SOHO has found something very intriguing inside the sun— sounds. We all know sound cannot travel through space, but sound can certainly travel through the plasma of the sun. Sound waves course through the sun's interior, reflecting off the surface and back into the interior. SOHO has detected more than 10 million separate notes, each of which has a unique path through the sun.

As the sound waves move into the interior of the sun, they encounter increasingly denser material. The sound waves actually move faster as the density increase. Consequently, the sound waves will continuously refract through the plasma. Draw a circle representing the sun and show a possible path that a particular sound wave might take through the sun. Include at least three reflections off the surface.

Fact and Belief

<a onClick="window.open('/olcweb/cgi/pluginpop.cgi?it=jpg::::/sites/dl/free/0078458137/193800/ch17_stonehenge.jpg','popWin', 'width=NaN,height=NaN,resizable,scrollbars');" href="#"><img valign="absmiddle" height="16" width="16" border="0" src="/olcweb/styles/shared/linkicons/image.gif"> (6.0K)</a> An interesting fact is that Stonehenge is angled such that on the equinoxes and the solstices, the sun rising over the horizon appears to be perfectly placed between gaps in the megaliths. Another common belief, but untrue, is that on the equinox, day and night are equal length.

Well, all is not as it would seem. For instance, on the vernal equinox, March 20th, the daytime is ten minutes longer than the nighttime.

If you think really hard and review what you've learned in Chapter 17, then you can probably figure out the reason for the longer day on the vernal equinox. Here is a hint: If Earth's atmosphere was the same as Mercury's atmosphere, then the equinox would be the true day of equality between night and light.