40 PART 1^ |^ EXPLORING THE SKY
Path of total eclipse MoonSunlightab Visual■ Figure 3-8
(a) The umbra of the moon’s shadow sweeps from west to east across Earth, and observers in the path of totality see a total solar eclipse. Those outside the
umbra but inside the penumbra see a partial eclipse. (b) Eight photos made by a weather satellite have been combined to show the moon’s shadow moving
across Mexico, Central America, and Brazil. (NASA GOES images courtesy of MrEclipse.com)
Closest Farthest Closest Farthest
VisualAngular size of moon Angular size of sunPath of annular eclipse MoonSunlightDisk of sunAnnular eclipse of 1994Disk of moon centered
in front of the sunThe angular diameters of the moon and
sun vary slightly because the orbits of the
moon and Earth are slightly eliptical.If the moon is too far from Earth
during a solar eclipse, the umbra
does not reach Earth’s surface.■ Figure 3-9
Because the angular diameter of the moon and the sun vary slightly, the disk of the moon is sometimes too small to cover the disk of the sun.
This means the umbra of the moon does not reach Earth, and the eclipse is annular. From Earth, you see an annular eclipse because the moon’s
angular diameter is smaller than the angular diameter of the sun. In the photograph of the annular eclipse of 1994, the dark disk of the moon
is almost exactly centered on the bright disk of the sun. (Daniel Good)