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What can a century-old photograph tell us about a changing sky?

An old astronomical glass plate preserves an observation that cannot be made again today. Harvard’s plate archive brings such records into digital comparison, alongside dates, logbooks, and calibration work. The glass image alone is not the whole dataset; knowing how and when it was made changes what can be inferred from it.

8–10 min

Questions you could explore

  • What information would make two observations taken decades apart comparable?

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Space

Why does the Moon change shape during a month?

A crescent Moon is not a partly switched-off Moon. Sunlight still illuminates half of it, while its changing position around Earth changes how much of that lit half we can see.

3–5 min

Why does the Moon change shape during a month?

Space3–5 minA crescent Moon is not a partly switched-off Moon. Sunlight still illuminates half of it, while its changing position around Earth changes how much of that lit half we can see.

Space

Two eclipses, two different shadows

A solar eclipse and a lunar eclipse both involve the Sun, Earth, and Moon, but the shadow falls in a different place. In one, the Moon’s shadow reaches Earth; in the other, the Moon moves into Earth’s shadow. The Moon’s tilted orbit helps explain why these alignments do not happen every month.

5–7 min

Two eclipses, two different shadows

Space5–7 minA solar eclipse and a lunar eclipse both involve the Sun, Earth, and Moon, but the shadow falls in a different place. In one, the Moon’s shadow reaches Earth; in the other, the Moon moves into Earth’s shadow. The Moon’s tilted orbit helps explain why these alignments do not happen every month.

Space

Why are planets round while some asteroids look like potatoes?

Pictures of planets often show smooth curves; pictures of small asteroids can resemble battered potatoes. Shape depends on the contest between gravity and the material’s ability to hold an uneven structure. Rotation adds another complication: even a large planet need not be a perfect sphere.

3–7 min

Why are planets round while some asteroids look like potatoes?

Space3–7 minPictures of planets often show smooth curves; pictures of small asteroids can resemble battered potatoes. Shape depends on the contest between gravity and the material’s ability to hold an uneven structure. Rotation adds another complication: even a large planet need not be a perfect sphere.

What can a century-old photograph tell us about a changing sky? | Speech Topic | speaking.app