Can I see half way round the world?

Thermo, from your vantage point you only see some 10 Km of the 40 000 Km 'around the world', whatever that may mean.

The Sun itself, if it could see, would see half of the world at any time. If the Sun was a big mirror, then you could also have seen half the world by looking into it. Only problem: it would have been too dark to see anything!

Stricktly speaking, an observer at any distance from the surface of the earth couldn't quite see "half the world" at one time!

Quote: "Strictly speaking, an observer at any distance from the surface of the earth couldn't quite see "half the world" at one time!"

Agreed. But in my hypothetical "mirror sun", if you shape it correctly, one could see more than half of the world!

Ok, I'll give you that one (now you've shaped the mirror!)

Jorrie,

I love your "sun mirror example," with your permission, I would like to use it. (credits given of course...)

Wangito

Hi Wangito, you're welcome to use this 'example'. It was just a tongue in the cheek comment!

Your scenario has the sun travelling around the earth. You (and the earth) are the travellers, not the sun. If your view was limited to a fraction of what you could normally see, the duration would still be 12 hours (unless you were viewing the sky through a vertical tube of great length).

While one cannot see halfway around the world, on a clear night, you can see more than half the visible universe. Also, because the sun is bigger in diameter than the earth and because the atmosphere bends light at the horizon, the length of time you can see the sun is greater than 12 hours per day at the equator.

Could you please explain what you mean by "more than half the visible universe"?

Assuming the boat the observer is on is typical, so when he is on deck, he is above sea level, decreasing the amount the Earth is blocking his view. Second, the Earth is bulged slightly at the equator, so north and south view is better than east and west. Third, the atmosphere bends light at the horizon allowing one to see "around the corner".

Guess I don't understand this thread. It seems to me the distance that we could view is linked to the diameter of the earth. If the earth is approx. 14,000 miles in dia. we could only see the distance subtended by the arctangent of that distance, the difference being our height above sea level? Am I missing something?

That's one tall dude!!

Hi

1. Since the 16th century we are traveling around the sun and not vise-verse. do you remember that they burnt him for this?

2. the human eye will only see,and that is under optimal conditions, approximately 15 to 25 miles.("see" means you can see details, and up to 45 deg head elevation). Therefore the answer to you question is NO. you can not see half of the world.

3: BUT, if for argument sake we will replace the human eye, say for hi-power laser pointer, and if there are no optical obstacles in all directions, (calm sea, for example) all the way to the horizon, and due to the atmosphere "bending effect", theoretically you will be able to see about 182 degrees of visible campsite. if you now rotate the laser pointer 360 deg. and updown, you being the center, than you get a dome shaped type campsite which means your laser pointer gets to "see" just a little bit more than Half of the visible universe.

"Seeing is believing..."

Wangito

Sorry, but I still object to (quote) "you can see more than half the visible universe".

If it's visible, you may be able to see it. If it's not, you can't (by definition).

Quote: "Sorry, but I still object to (quote) "you can see more than half the visible universe"."

Yea, the term "visible universe" is too loose. I think the meaning was "observable universe", which is all that we can observe now, all vantage point taken together.