The Solar System

42 PART 1^ |^ EXPLORING THE SKY

Dense fi lters and exposed fi lm do not necessarily provide protection

because some fi lters do not block the invisible heat radiation (infra-

red) that can burn the retina of your eyes. Dangers like these have

led offi cials to warn the public not to look at solar eclipses at all and

have even frightened some people into locking themselves and

their children into windowless rooms. It is a Common Mis-

conception that sunlight is somehow more dangerous during an

eclipse. In fact, it is always dangerous to look at the sun. Th e danger

posed by an eclipse is that people are tempted to ignore common

sense and look at the sun directly, which can burn their eyes.

Th e safest and simplest way to observe the partial phases of a

solar eclipse is to use pinhole projection. Poke a small pinhole in a

sheet of cardboard. Hold the sheet with the hole in sunlight and

allow light to pass through the hole and onto a second sheet of

cardboard (■ Figure 3-12). On a day when there is no eclipse, the

result is a small, round spot of light that is an image of the sun.

During the partial phases of a solar eclipse, the image will show the

dark silhouette of the moon obscuring part of the sun. Pinhole

b

a

A Total Solar Eclipse

The moon moving

from the right just

begins to cross in

front of the sun.

The disk of the

moon gradually

covers the disk of

the sun.

Sunlight begins

to dim as more of

the sun’s disk is

covered.

During totality,

pink prominences

are often visible.

A longer-exposure

photograph during

totality shows the

fainter corona.

■ Figure 3-10

This sequence of photos shows the fi rst half of a total solar eclipse. (Daniel
Good)

space, but eclipse enthusiasts still journey to exotic places for the
thrill of seeing a total solar eclipse.
No matter how thrilling a solar eclipse is, you must be cautious
when viewing it. During the partial phase, part of the sun remains
visible, so it is hazardous to look at the eclipse without protection.

■ Figure 3-11

(a) During a total solar eclipse, the moon covers the photosphere, and the

ruby-red chromosphere and prominences are visible. Only the lower corona is

visible in this image. (©2005 by Fred Espenak) (b) The diamond ring effect can

sometimes occur momentarily at the beginning or end of totality if a small

segment of the photosphere peeks out through a valley at the edge of the

lunar disk. (National Optical Astronomy Observatory)