Time Challenge

The phases of the moons of Mars, Jupiter, and Saturn could provide a relatively good clue for the day, and maybe down to the hour, if you have the data. Also, if your scope has the resolution you could possibly see the great red spot of Jupiter. If you have data on its position, then you have a shot at getting down to the hour or maybe even better if you're a careful observer.

Then there are the transitions of Saturn's and Jupiter's moons' shadows across those planets. That may improve your measurement ability.

Finally, the best method is to order some pizza and have it delivered by FedEx guaranteed next-day 8:00 AM delivery! Those guys are spot on!

Just to clarify, the phases of the moons really is the orbital position of the moons relative to their planet and not the visual phase (i.e., full moon, quarter moon, etc.).

If you are out sailing on the sea , and the sun is out - who cares what the time is?

Andy

your on holidays enjoy

worry about food and water first

this is why i dont like sailing

Jorrie, you did not mention the phase of the moon, but I'm sure one can use occultation of stars by the moon to determine time fairly accurately, no so? This obviously assumes that you have accurate occultation data.

Quoting Guest: "Jorrie, you did not mention the phase of the moon, but I'm sure one can use occultation of stars by the moon to determine time fairly accurately, no so?"

Yep, this can be used as a rough estimate of time, but due to the closeness of the Moon to Earth, the time of occultation can differ by more than an hour (I think), depending on where you are on the Earth. For marine navigation, you need time accurate to within seconds, or you may be grounded somewhere!

As an aside, astronomers use the difference in the time of occultations between various places on Earth to determine the Moon's exact position in space and thus refine its orbital parameters.

You could possibly calculate your longitude by looking at the angle between the moon and sun.

The theory goes like this. Take a point on the earth where the moon and sun rise at the same time. Now look at a point opposite or 180º from this. The sun would rise 12 hours later but by that time the moon would have moved a further 6.588º in the sky. This figure is taken from the fact that the moon takes 27.32166155 days to orbit the earth which means that it travels through 13.176º every day or 6.588º in 12 hours.

So by calculating where the moon was at sunrise at Greenwich and comparing it to the position of the moon at sunrise at your location you could in theory calculate your longitude. If it were and equinox and the moon was in an equatorial orbit the difference in elevation multiplied by 27.3216 would give you your longitude. Hopefully you would be smart enough to know if you were East or West so I've left that part out.

In reality however you need to compensate for the angle of the lunar orbit to the axis of the earth and also the offset of the earths axis to its orbit around the sun and I don't know how to allow for these but at least it's a theory.

Quote: "You could possibly calculate your longitude by looking at the angle between the moon and sun."

Masu, although it's not quite the answer to the question, it may just work for finding your longitude, since you have your latitude from the Sun's elevation as it crosses your meridian.

As you said, the Sun's and (especially) the Moon's paths are pretty weird. You would need complex spherical geometry to translate the rising/setting positions and times of the Sun and the Moon from your measured angles to the UT meridian.

Seems I recall reading someplace that Mr. Kepler had the idea of using the position of the moons of Jupiter as a celestial clock to calculate longitude.