Final answer:
Earth's shadow always consists of both an umbra and a penumbra. The statement suggesting that Earth's shadow can have only an umbra without a penumbra is false.
Step-by-step explanation:
The Earth's shadow cannot have only one umbra without a penumbra. When a light source like the Sun is larger than the Earth, the shadow of the Earth consists of two distinct parts: the dark inner region called the umbra where all direct light is blocked, and the lighter, more diffused region surrounding it called the penumbra, where some light is still visible. This is evident during solar eclipses, as demonstrated in Figure 4.21 of the provided material, where different types of eclipses can be observed depending on the position within the Earth's shadow. Therefore, the statement that Earth's shadow can have only one umbra and not a penumbra is false.