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11 votes

How does the Moon look like from different latitudes of the Earth?

Here are some answers to your various comments and questions: you can estimate a direction of south True, but it would be a very rough approximation at best. In order for it to be accurate, the ...
JohnHoltz's user avatar
  • 8,032
9 votes

Is it possible to determine an observer's position on Earth from a photo of the night sky and the time of the shot?

What can you tell from a picture of some stars? At the very least, you need a recognisable asterism If the exposure is too low or the light pollution too high to identify unambiguously an asterism ...
Ingolifs's user avatar
  • 4,155
9 votes

Earth's Rotation & Longitude

Both is correct. It just depends which way you look. Greenwich is by definition at longitude 0°. As the Sun moves 15° per hour from East to West. You can simply do the equation if you know your ...
planetmaker's user avatar
  • 19.9k
8 votes

Determining latitude and longitude in bad weather

Sunstones are believed to have been used by vikings to determine the direction to the Sun on cloudy days. That helps you point the ship in the right direction, and by experience you can estimate the ...
LocalFluff's user avatar
  • 11.4k
7 votes

Determining latitude and longitude in bad weather

When it's cloudy at sea, the one measurement one still has is approximate sunrise or sunset, which can be used to determine longitude, but the uncertainty is very large, in particular at higher ...
gerrit's user avatar
  • 2,233
6 votes

Earth's Rotation & Longitude

Your location is west of the International Date Line. The time of sunrise gets later and later in terms of UTC time as one's location moves to the west from the Greenwich meridian because the Sun ...
David Hammen's user avatar
  • 34.1k
5 votes

70-year star in Talmud confusing sailors?

Comets can look like stars. Sometimes the outside of the coma and tail of the comet are too faint to see with the naked eye, and only the central part of the coma is bright enough to be seen. In this ...
James K's user avatar
  • 125k
5 votes
Accepted

How do we give directions in space?

You need to define an agreed standard for orientation of axis and origin. What co-ordinate system you choose as a standard depends on your purpose. Here are some examples and links : Celestial ...
StephenG - Help Ukraine's user avatar
5 votes
Accepted

Will time that moon crosses meridian always be periodic?

Your formula is a crude approximation. It's ok if you just want a rough idea of the number of orbits the Moon makes over a long period of time, but it's not useful for calculating the daily motion of ...
PM 2Ring's user avatar
  • 15k
5 votes
Accepted

(Fiction) How would a time traveler locate himself with 1962 technology?

Your semi-intuitive thought that there must be a pattern of the planet locations that would show the date is correct, I think. You won't need any special equipment but a sextant which will measure ...
stretch's user avatar
  • 1,797
4 votes

Celestial navigation from scratch

To expand a little on James's answer: The pole angle method doesn't care what time of year it is, the celestial pole isn't going anywhere. ;) However, if you're in the tropics, the altitude of the ...
PM 2Ring's user avatar
  • 15k
4 votes

Where will the planned Deep Space Atomic Clock orbit "after" Earth?

"The instrument will be tested in Earth orbit for one year, ..." What would it then orbit? It will continue to orbit the Earth, at least for a while. It will eventually end up not orbiting ...
David Hammen's user avatar
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4 votes
Accepted

North Stars of each Solar system planet?

Answer based on Is Polaris the north star for all the other planets just like it is for Earth? and What star is directly north of the suns north pole? Planet Pole Star Sun* There is no bright star ...
GrapefruitIsAwesome's user avatar
4 votes

Questions about Celestial Navigation

GHA = Greenwich Hour Angle, but not Greenwich Celestial Meridian—actually, there’s no such thing. I suppose you meant the Celestial Prime Meridian (or 0° of celestial longitude). GHA is the angle in ...
Pierre Paquette's user avatar
4 votes

Earth's Rotation & Longitude

You are 10 hours ahead of Greenwich... and so you have the sun overhead 10 hours before Greenwich roughly. Which is about the 146° between your locations (in the Eastern Hemisphere), divided by 15°. ...
JeopardyTempest's user avatar
4 votes

Practice noon sight in Colorado?

There are relatively simple practice bubble levels available for most sextants. I have used one of this type, consisting of a tube and bubble that replaces the standard eyepiece/telescope. It cannot ...
amateurAstro's user avatar
  • 1,780
4 votes
Accepted

Celestial Navigation - How to calculate Longitude?

You observed the apparent solar time, but in order to compute longitude you need the mean solar time. The difference between the two is the equation of time, a combined effect of (1) the obliquity ...
Mike G's user avatar
  • 18.7k
3 votes

consider you are stranded in deep space, and an alien agreed to drop you back home, how would you explain the location of earth in the galaxy?

There are a number of questions about interstellar navigation in general and findng Earth in particular, in the Worldbuilding Stack Exchange. I have answered some of them. https://worldbuilding....
M. A. Golding's user avatar
3 votes

consider you are stranded in deep space, and an alien agreed to drop you back home, how would you explain the location of earth in the galaxy?

You need to find markers that are easily explained and easily visible. This is likely to require a lot of knowledge of astronomy. You first find the Crab pulsar (the brightest(?) gamma/X-ray source in ...
Rob's user avatar
  • 2,035
3 votes

Where will the planned Deep Space Atomic Clock orbit "after" Earth?

The DSAC to be launched in June 2019 is a Technology Demonstration Mission, in which they only test whether it works as well in space as it does on the ground. If it passes the tests, similar devices ...
Mike G's user avatar
  • 18.7k
3 votes
Accepted

Could pulsar navigation replace GPS

Pulsar, or X-ray navigation is being actively tested right now. Currently an X-ray telescope mounted on the International Space Station completed a test where a small navigation computer was able to ...
uhoh's user avatar
  • 30.7k
3 votes
Accepted

What are the key coordinate systems used in Astronomy, and where are they used?

Navigating the solar system, you'd probably track your probe using Earth-based radio telescopes in the equatorial ICRF, though you might describe the overall trajectory in terms of the ecliptic. ...
Mike G's user avatar
  • 18.7k
3 votes

What's the soonest Oumuamua could return?

Oumuamua as an object is remarkable, because it has a positive net energy, which means it is not bound to the gravitational well of our sun. Therefore it will never return.
AtmosphericPrisonEscape's user avatar
3 votes

Celestial navigation from scratch

One's latitude is easy to establish. You just need to find the angle of elevation of the pole, the point about which the stars appear to revolve each night. A stick and a plumb line can do this. One'...
James K's user avatar
  • 125k
3 votes

Lunar Librations and Subsolar Point in Matlab

Answer provided by @PM2Ring, who linked to The JPL Planetary and Lunar Ephemerides DE440 and DE441 which contained the necessary calculation. The main issue was the was the angles were being rotated ...
Timothy Barrett's user avatar
2 votes

Determining latitude and longitude in bad weather

First off, there is evidence to suggest that sunstones were used to find the direction of the sun on cloudy days. However the compass has completely eliminated the need for a sunstone as it works in ...
thinkerinthedark's user avatar
2 votes

How to find a deep sky object 1° NE from a given star

Usually when the direction to an object is given relative to a star, the directions are related to equatorial coordinates (the coordinates on the sky). They are not related to the compass or cardinal ...
JohnHoltz's user avatar
  • 8,032
2 votes

How to calculate local position, knowing the RA and Dec of the center of an image, RPY of the camera, and precise time?

Picture was taken somewhere near 30°22'02.0"N 75°00'35.7"E Bathinda, Punjab, India. Answering your question about time - how it enters into the sight reduction: RA, all by itself, isn't ...
stretch's user avatar
  • 1,797
2 votes
Accepted

Why does the latitude of an observer affect the hour angle of a body in Stellarium?

I do not have Stellarium, so I cannot confirm what is causing it with 100% certainty. But by using JPL's Horizons website, I can confirm that the position on the Earth's surface changes the apparent ...
JohnHoltz's user avatar
  • 8,032
2 votes

consider you are stranded in deep space, and an alien agreed to drop you back home, how would you explain the location of earth in the galaxy?

...how would you explain the location of earth in the galaxy? I would first describe the two Voyager spacecraft to the aliens and tell them to go find at least one of them and bring it to me. I would ...
uhoh's user avatar
  • 30.7k

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