3 ms·

does anyone know if astro navigation systems deduce time from star transits (or rather generalized star transits, so they don't need to actually be momentarily

does anyone know if astro navigation systems deduce time from star transits (or rather generalized star transits, so they don't need to actually be momentarily collinear, i.e. a database of stars with their distances included)?

dproblem 8y ago
Yes, they do. The only time it works is when you have a clear view, which is not always.
planteen 8y ago
The article mentions a "highly accurate chronometer" in regards to the Blackbird. So I don't think they deduce time from the stars. Rhubidium atomic clocks are quite compact and not all that expensive. Hobbyist electronics people buy retired ones from cell phone base stations for an accurate 10 MHz sync signal in their home labs. https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-frequency-standard/comment-page-4/ https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-freq...
joshvm 8y ago
The SR-71 carried a clock accurate to a hundredth of a second [1]. It used that, combined with current observed locations of the brightest stars in the field of view to determine location (with reference to a catalogue). More info here: https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg=PA65&dq=sr-71+chronometer+accuracy&source=bl&ots=pwGcwkO8ZI&sig=ACfU3U3YySJdhfKYta20kOoI6LyXU72nrw&hl=en&sa=X&ved=2ahUKEwjt-u6mpqrhAhUTsHEKHXKcCFkQ6AEwCnoECBsQAQ#v=onepage&q=sr-71%20chronometer%20accuracy&f=false https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg... What do you mean by a transit in this case?
- DoctorOetker 8y ago
  it is possible to deduce location of the earth on its orbit around the sun, and hence the time by star transits: https://en.wikipedia.org/wiki/Transit_instrument https://en.wikipedia.org/wiki/Transit_instrument consider for example 2 very distant stars, and a closer star in the middle, and all of them in a plane perpendicular to the ecliptic. as the earth rotates, the closest star seems to move left/right with respect to the "vertical" defined by the more distant stars. from such a star transit you know the earth has just passed through the plane defined by these stars, and hence know the earth's position, hence the time. in the past catalogues for transits were optimized for human use, i.e. close to each other, ... but a modernized i.e. software solution should not need such proximity, and could make use of all the visible stars to make a more accurate assessment. I was kind of asking if there were any free open source software, it would be kind of neat to have an emergency laptop (with some optics) loaded with openstreetmap and astronomical positioning software, ...
  - rocqua 8y ago
    I might be off here, but it seems like resolution would be a real issue. The variation you are looking for has a period of 1 year. To get hour accuracy out of that you'd need to be able to distinguish 356*24 different relative positions of these stars. It seems to me like camera's aren't going to be supplying that kind of data.

dproblem 8y ago

Yes, they do. The only time it works is when you have a clear view, which is not always.

planteen 8y ago

The article mentions a "highly accurate chronometer" in regards to the Blackbird. So I don't think they deduce time from the stars. Rhubidium atomic clocks are quite compact and not all that expensive. Hobbyist electronics people buy retired ones from cell phone base stations for an accurate 10 MHz sync signal in their home labs. https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-frequency-standard/comment-page-4/ https://www.eevblog.com/2012/01/14/eevblog-235-rubidium-freq...

joshvm 8y ago

The SR-71 carried a clock accurate to a hundredth of a second [1]. It used that, combined with current observed locations of the brightest stars in the field of view to determine location (with reference to a catalogue). More info here: https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg=PA65&dq=sr-71+chronometer+accuracy&source=bl&ots=pwGcwkO8ZI&sig=ACfU3U3YySJdhfKYta20kOoI6LyXU72nrw&hl=en&sa=X&ved=2ahUKEwjt-u6mpqrhAhUTsHEKHXKcCFkQ6AEwCnoECBsQAQ#v=onepage&q=sr-71%20chronometer%20accuracy&f=false https://books.google.co.uk/books?id=6svmtOFa1JIC&pg=PA65&lpg... What do you mean by a transit in this case?

DoctorOetker 8y ago
it is possible to deduce location of the earth on its orbit around the sun, and hence the time by star transits: https://en.wikipedia.org/wiki/Transit_instrument https://en.wikipedia.org/wiki/Transit_instrument consider for example 2 very distant stars, and a closer star in the middle, and all of them in a plane perpendicular to the ecliptic. as the earth rotates, the closest star seems to move left/right with respect to the "vertical" defined by the more distant stars. from such a star transit you know the earth has just passed through the plane defined by these stars, and hence know the earth's position, hence the time. in the past catalogues for transits were optimized for human use, i.e. close to each other, ... but a modernized i.e. software solution should not need such proximity, and could make use of all the visible stars to make a more accurate assessment. I was kind of asking if there were any free open source software, it would be kind of neat to have an emergency laptop (with some optics) loaded with openstreetmap and astronomical positioning software, ...
- rocqua 8y ago
  I might be off here, but it seems like resolution would be a real issue. The variation you are looking for has a period of 1 year. To get hour accuracy out of that you'd need to be able to distinguish 356*24 different relative positions of these stars. It seems to me like camera's aren't going to be supplying that kind of data.