Celestial Navigation Question

[scotty123]

If I am exactly on the Equator, looking at the Sun, which is also exactly on the Equator, how far around the 'bulge' of the Earth can I see the Sun from?

Answers please in degrees of Longitude.

 

[bedouin]

To a first order approximation it is 90 degrees - if you want a more accurate answer you will need to define "see" and other terms...

 

[AndrewB]

Height of eye, please?
All of sun or just top edge?
Do you want allowance for atmospheric refraction, or not?

 

[landaftaf]

like height of eye

 

[tcm]

ah, but how tall are you? If you were, say, 10,000 miles tall you could right around the back of he earth and just lean around a bit

 

[FWB]

About 195 deg at sea level. Just a guess /forums/images/graemlins/smile.gif

 

[stephenh]

180 degrees direct
+ an extra 1 each end because thats how wide it appears to be to us ( allowing that you will see just the edge)
plus an extra 1/2 diameter at each end to allow for refraction = 1 degree.

= 183 degrees, now add on for height of eye.

I'm sure I've missed something.........

 

[Richard10002]

Why do you want to know?

 

[FWB]

I thought he knew. If he wants to know then download sunclock 6 and have a look at where its light and dark.

 

[Sixpence]

That's handy , maybe I shouldn't ring New Zealand at the moment though /forums/images/graemlins/grin.gif

 

[tangomoon]

Hmm I must away, the intelligentsia have arrived to baffle us with bull

 

[Richard10002]

Aha! It's a quiz question then?

 

[scotty123]

"Height of eye, please?"

About 2 metres

"All of sun or just top edge?"

Lower limb

"Do you want allowance for atmospheric refraction, or not?"

I did say 'see it', so one assumes that refraction would not be a factor.

"Why do you want to know?"

SWMBO, asked the question.
Her oppinion, is that it would be about 3 miles if just on the horizon, up to 90 degrees when higher.

"180 degrees direct" "About 195 deg at sea level. Just a guess"

So, at noon when at Greenwich, 0 longitude, the Sun can be seen from the International Date Line & beyond? Using mirrors perhaps? /forums/images/graemlins/tongue.gif

 

[snowleopard]

The sun would not be on the equator but 93000000 miles above it so I presume you are talking about the sun's Ground Position. The answer is going to be 90° plus corrections for height of eye and refraction. You said you wanted the lower limb which is handy because the rule of thumb is that when the sun's centre is on the horizon, refraction makes it appear so the lower limb is touching the horizon so the two corrections cancel each other out.. Height of eye will only make a difference of around 5 minutes of arc.

In summary - extremely close to 90°

 

[FWB]

[ QUOTE ]


"180 degrees direct" "About 195 deg at sea level. Just a guess"

So, at noon when at Greenwich, 0 longitude, the Sun can be seen from the International Date Line & beyond? Using mirrors perhaps? /forums/images/graemlins/tongue.gif

[/ QUOTE ]

NO, I reckon that you can see the sun from two lines of longitude 195 deg apart.

Download Sunclock 6 and have a look for yourself.

Actually having a closer look, I reckon its 180 deg.

 

[alant]

Assuming you were using a sextant, the greatest distance surely, would be when the Sun has its upper limb at the horizon. (This is a simple model, to match my mind)

Forgetting about all the corrections involved, which I'm sure the more mathematically qualified will aquaint you with, this distance is 90 degrees - Sextant Angle = Zenith Distance.
So its unlikely to be more than 90 degrees.

------------------------------------------------------------------------
"NO, I reckon that you can see the sun from two lines of longitude 195 deg apart.

Download Sunclock 6 and have a look for yourself.

Actually having a closer look, I reckon its 180 deg."

Can't see how it could be 180 degrees, perhaps you could explain in more detail.

 

[Cruiser2B]

[ QUOTE ]
the rule of thumb is that when the sun's centre is on the horizon, refraction makes it appear so the lower limb is touching the horizon

[/ QUOTE ]

I believe the rule of thumb is that when SS/SR occurs (the upper limb is at the actual horizon), refraction makes it appear that the entire sun's disc is half a diameter above the visible horizon.