48 PART 1^ |^ EXPLORING THE SKY
- If on March 1 the full moon is near the Favorite Star Spica, when will
the moon next be full? When will it next be near Spica? - How many times larger than the moon is the diameter of Earth’s umbral
shadow at the moon’s distance? (Hint: See the photo in Figure 3-3.) - Use the small-angle formula to calculate the angular diameter of Earth
as seen from the moon. - During solar eclipses, large solar prominences are often seen extending
5 arc minutes from the edge of the sun’s disk. How far is this in
kilometers? In Earth diameters? - If a solar eclipse occurs on October 3: (a) Why can’t there be a lunar
eclipse on October 13? (b) Why can’t there be a solar eclipse on
December 28? - A total eclipse of the sun was visible from Canada on July 10, 1972.
When did eclipse occur next with the same sun-moon-Earth geometry?
From what part of Earth was it total? - When will the eclipse described in Problem 9 next be total as seen
from Canada? - When will the eclipse seasons occur during the current year? What
eclipse(s) will occur?
Learning to Look
- Use the photos in Figure 3-1 as
evidence to show that the moon
always keeps the same side fac-
ing Earth. - Draw the umbral and penumbral
shadows onto the diagram in
the middle of page 34. Use the
diagram to explain why lunar
eclipses can occur only at full
moon and solar eclipses can oc-
cur only at new moon. - Can you detect the saros cycle in
Figure 3-15? - The stamp at right shows a
crescent moon. Explain why the
moon could never look this way. - The photo at right shows the
annular eclipse of May 30,
1984. How is it different from
the annular eclipse shown in
Figure 3-9?
Review Questions
- Which lunar phases would be visible in the sky at dawn? At midnight?
- If you looked back at Earth from the moon, what phase would Earth
have when the moon was full? New? A fi rst-quarter moon? A waxing
crescent? - If a planet has a moon, must that moon go through the same phases
that Earth’s moon displays? - Could a solar-powered spacecraft generate any electricity while passing
through Earth’s umbral shadow? Through Earth’s penumbral shadow? - If a lunar eclipse occurred at midnight, where in the sky would you
look to see it? - Why do solar eclipses happen only at new moon? Why not every new
moon? - Why isn’t the corona visible during partial or annular solar eclipses?
- Why can’t the moon be eclipsed when it is halfway between the nodes
of its orbit? - Why aren’t solar eclipses separated by one saros cycle visible from the
same location on Earth? - How could Thales of Miletus have predicted the date of a solar eclipse
without observing the location of the moon in the sky? - How Do We Know? Some people think science is like a grinder that
cranks data into theories. What would you tell them about the need for
scientists to be creative and imaginative?
Discussion Questions
- How would eclipses be different if the moon’s orbit were not tipped
with respect to the plane of Earth’s orbit? - Are there other planets in our solar system from whose surface you
could see a “lunar” (moon) eclipse? A total solar eclipse? Which ones
and why?
Problems
- Identify the phases of the moon if on March 20 the moon is located
at the point on the ecliptic called (a) the vernal equinox, (b) the
autumnal equinox, (c) the summer solstice, (d) the winter solstice. - Identify the phases of the moon if at sunset the moon is (a) near the
eastern horizon, (b) high in the southern sky, (c) in the southeastern
sky, (d) in the southwestern sky. - About how many days must elapse between fi rst-quarter moon and
third-quarter moon?