Cosmic Distance Ladder on Instagram: "Anaxagoras (c. 500 BCE) is one of the earliest natural philosophers we know of to propose what is essentially the modern explanation of eclipses, which is that they are caused when the positions of the Earth, Moon, and Sun line up in such a way that the shadow of the Earth falls on the Moon (a lunar eclipse), or the shadow of the Moon falls on the Earth (a solar eclipse). The ancient Greeks also gave us the term for this type of alignment: syzygy (which means ‘paired together’). The Ancient Greek model explains other features of eclipses with relatively few additional assumptions. For instance, one can observe that lunar eclipses happen during what would otherwise be a full Moon, and solar eclipses happen during what would otherwise be a new Moon. Similarly, once one accepts the additional axiom that the Moon orbits the Earth in a roughly circular (but perhaps inclined) orbit once every lunar month (about four weeks), one can also explain the observed phenomenon that lunar and solar eclipses tend to come in pairs that are half a lunar month (or two weeks) apart; for instance, the partial solar eclipse occurring on Saturday, March 29th (this weekend!) is paired with the total lunar eclipse from last week. Indeed, this is the time needed for the Moon to move from a syzygy of opposition to the Sun to one of conjunction, or vice versa. Aristarchus cleverly used both lunar and solar eclipses, as well as the half-Moon phases, to determine the size and distances of both the Moon and Sun. We’ll go into this story in great detail in the book, but in the meantime you can check out the video with @3blue1brown on this at: https://youtu.be/YdOXS_9_P4U?t=488 (and in the Linktree in our bio!) #DistanceLadder #astronomy #LunarEclipse #SolarEclipse #syzygy #AncientAstronomy #GreekAstronomy #mythology #TotalLunarEclipse2025 #PartialSolarEclipse2025"

13 likes, 0 comments - cosmic_distance_ladder on March 23, 2025: "Anaxagoras (c. 500 BCE) is one of the earliest natural philosophers we know of to propose what is essentially the modern explanation of eclipses, which is that they are caused when the positions of the Earth, Moon, and Sun line up in such a way that the shadow of the Earth falls on the Moon (a lunar eclipse), or the shadow of the Moon falls on the Earth (a solar eclipse). The ancient Greeks also gave us the term for this type of alignment: syzygy (which means ‘paired together’). The Ancient Greek model explains other features of eclipses with relatively few additional assumptions. For instance, one can observe that lunar eclipses happen during what would otherwise be a full Moon, and solar eclipses happen during what would otherwise be a new Moon. Similarly, once one accepts the additional axiom that the Moon orbits the Earth in a roughly circular (but perhaps inclined) orbit once every lunar month (about four weeks), one can also explain the observed phenomenon that lunar and solar eclipses tend to come in pairs that are half a lunar month (or two weeks) apart; for instance, the partial solar eclipse occurring on Saturday, March 29th (this weekend!) is paired with the total lunar eclipse from last week. Indeed, this is the time needed for the Moon to move from a syzygy of opposition to the Sun to one of conjunction, or vice versa. Aristarchus cleverly used both lunar and solar eclipses, as well as the half-Moon phases, to determine the size and distances of both the Moon and Sun. We’ll go into this story in great detail in the book, but in the meantime you can check out the video with @3blue1brown on this at: https://youtu.be/YdOXS_9_P4U?t=488 (and in the Linktree in our bio!) #DistanceLadder #astronomy #LunarEclipse #SolarEclipse #syzygy #AncientAstronomy #GreekAstronomy #mythology #TotalLunarEclipse2025 #PartialSolarEclipse2025".

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