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What can century-old photographs reveal about stars today?

A star photographed on a glass plate a century ago can become a new measurement when compared with later observations. Harvard's DASCH project digitizes an astronomical plate archive, alongside dates and logbooks. Explore how calibration makes those old images useful for investigating changes across decades.

8–10 min

Questions you could explore

  • What information would make two observations taken decades apart comparable?
  • How could digitizing astronomical plates make changes across decades easier to investigate?

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Space

A crescent Moon is not a partly switched-off Moon

Sunlight illuminates half the Moon, while its changing position around Earth changes how much of that lit half we can see. A phase is different from an eclipse, where one body blocks light from reaching another.

3–5 min

A crescent Moon is not a partly switched-off Moon

Space3–5 minSunlight illuminates half the Moon, while its changing position around Earth changes how much of that lit half we can see. A phase is different from an eclipse, where one body blocks light from reaching another.

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.

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