Final answer:
The solar corona is best observed during a total solar eclipse, which happens when the Moon fully covers the Sun, allowing the faint corona to be seen against the darkened sky.
Step-by-step explanation:
The solar corona is observable during a total solar eclipse. This occurs when the Moon moves directly between the Sun and Earth, completely covering the Sun's disk. The brightness of the photosphere, which is the visible surface of the Sun, usually outshines the corona, making it difficult to see.
However, during a total solar eclipse, the photosphere is obscured, revealing the faint glow of the solar corona extending millions of kilometers into space. Although the corona is visible from spacecraft using coronagraphs at any time, the best time to observe the corona from Earth is during the rare and spectacular event of a total solar eclipse, when the sky darkens enough for the pearly white corona to become visible.