6 ms·

Yes, but it's more complicated. The southern cross is quite a long way (like 30 degrees) from true south; we use it and a handful of other stars to find the bl

Yes, but it's more complicated. The southern cross is quite a long way (like 30 degrees) from true south; we use it and a handful of other stars to find the blank part of the sky where true South is. The other complicating factor is that Earth has a long "wobble" over the course of about 27,000 years (the technical term is "axial precession".) Right now, Polaris is within a degree of true north, but back in the fifth century it was 8 degrees away. In another 12 millennia true North will be all the way over by Vega. Likewise, the southern cross points somewhere vaguely close to true south, but how close it is varies from one millennium to the next.

na85 13y ago
Of course, in the fifth century I'm sure they neither knew nor cared that the North star was a few degrees off of actual North. It's not really relevant if the navigation error only changes by less than a degree over the course of a lifetime. The earliest navigators in Sumer in the 4th millennium BCE wouldn't care if a particular constellation points 5 or 20 degrees away from North.
- lotharbot 13y ago
  > "I'm sure they neither knew nor cared" They did, actually -- Pytheas had observed that true North was "devoid of stars" way back in 320 BC. Polaris didn't begin to be recognized as the "North Star" until much later (10th century according to wikipedia), because it wasn't particularly close. Navigators learned how to find where north was from several stars; it's only been the last several centuries that Polaris has been close enough to North as to be treated as the default for navigation. They also knew about precession (credited to Hipparchus in the 2nd century BC, but possibly an older discovery.) So they knew that north wouldn't be in exactly the same place centuries later. Differences of a few degrees were a pretty big deal to people who both navigated by, and gave religious significance to, the stars. I don't know the details of early Sumerian astronomical navigation schemes. From what I understand, our knowledge of their astronomy comes from Babylonian sources a couple thousand years later, and is not particularly detailed or reliable.

na85 13y ago

Of course, in the fifth century I'm sure they neither knew nor cared that the North star was a few degrees off of actual North. It's not really relevant if the navigation error only changes by less than a degree over the course of a lifetime. The earliest navigators in Sumer in the 4th millennium BCE wouldn't care if a particular constellation points 5 or 20 degrees away from North.

lotharbot 13y ago
> "I'm sure they neither knew nor cared" They did, actually -- Pytheas had observed that true North was "devoid of stars" way back in 320 BC. Polaris didn't begin to be recognized as the "North Star" until much later (10th century according to wikipedia), because it wasn't particularly close. Navigators learned how to find where north was from several stars; it's only been the last several centuries that Polaris has been close enough to North as to be treated as the default for navigation. They also knew about precession (credited to Hipparchus in the 2nd century BC, but possibly an older discovery.) So they knew that north wouldn't be in exactly the same place centuries later. Differences of a few degrees were a pretty big deal to people who both navigated by, and gave religious significance to, the stars. I don't know the details of early Sumerian astronomical navigation schemes. From what I understand, our knowledge of their astronomy comes from Babylonian sources a couple thousand years later, and is not particularly detailed or reliable.