How big is earth in moon sky...?

"Paul Lawler" wrote in message
...
"Dave" wrote in message
...
Barry Schwarz wrote:
On Thu, 1 Jul 2004 18:02:58 +1000, "Whisper"
wrote:

I assume it would appear 4 times bigger than the moon does in our
sky...?

You know, or can find, the distance from the Earth to the Moon. Same
for Earth's diameter. All you need is a spreadsheet or calculator
with an arctan function.

Just the multiply and divide keys should be sufficient for most
purposes.
Since the angle subtended by the moon is about 30 arcmin, which is
pretty
small, we can get away with small angle approximations. The moon's
diameter
is ~3476km, the earth's 12756km (equatorial). So the earth should appear
~30*12756/3476 arcmin or 1.8 degrees across in the sky to someone on the
moon. That's about the same angle the width of your thumb subtends at
the
eye when held at arms length.

And so to answer his original question, since the moon appears about 1/2 a
degree across in our sky, yes, that's about 4 times bigger.




Thank you.

That's quite a big object isn't it.........? I guess you could discern
certain landmarks? Maybe great wall of China with a telescope for eg...?

That's quite a big object isn't it.........? I guess you could discern
certain landmarks? Maybe great wall of China with a telescope for eg...?


Of course you could see landmarks - you would be able to easily recognise
the continents with the naked eye (is the Pacific Ocean a landmark?).

If you mean man made landmarks, certainly with a telescope. The easiest
would be city lights at night; I would imagine that these would be visible
with only a very modest telescope. For daytime recognition, you need a large
object with a high contrast to its surroundings - perhaps some large city in
a desert (LA?).

You wouldn't be able to see the great wall of China, even with a very
powerful telescope. Whilst I haven't been there, my understanding is that it
is only about 30 metres wide. I do not believe any existing telescope on
earth can resolve a line that narrow at that distance - indeed, the house I
am sitting in right now is probably wider than the Great Wall of China, so
if you could see the Great Wall of China from the moon you would also be
able to see my house ... I don't think so!

That's quite a big object isn't it.........? I guess you could discern
certain landmarks? Maybe great wall of China with a telescope for eg...?


Of course you could see landmarks - you would be able to easily recognise
the continents with the naked eye (is the Pacific Ocean a landmark?).

If you mean man made landmarks, certainly with a telescope. The easiest
would be city lights at night; I would imagine that these would be visible
with only a very modest telescope. For daytime recognition, you need a large
object with a high contrast to its surroundings - perhaps some large city in
a desert (LA?).

You wouldn't be able to see the great wall of China, even with a very
powerful telescope. Whilst I haven't been there, my understanding is that it
is only about 30 metres wide. I do not believe any existing telescope on
earth can resolve a line that narrow at that distance - indeed, the house I
am sitting in right now is probably wider than the Great Wall of China, so
if you could see the Great Wall of China from the moon you would also be
able to see my house ... I don't think so!

Hi Odysseus The greatest picture of the Earth is the one taken as it
came up over the moon's horizon. It is hanging in my den,and I blew it
up to 3 by 5 feet. That picture reminds me that there was a time NASA
had the right stuff. Bert

Hi Odysseus The greatest picture of the Earth is the one taken as it
came up over the moon's horizon. It is hanging in my den,and I blew it
up to 3 by 5 feet. That picture reminds me that there was a time NASA
had the right stuff. Bert

I take fast pictures,and they take up my time,and aggravation of my wife
opening my dark room door; However i did not have to blow up that
great Apollo picture taken by NASA.,and have it destroyed? NASA is OK
,but they went with the Shuttle,and that was a Rube Goldberg cartoon
Bert

I take fast pictures,and they take up my time,and aggravation of my wife
opening my dark room door; However i did not have to blow up that
great Apollo picture taken by NASA.,and have it destroyed? NASA is OK
,but they went with the Shuttle,and that was a Rube Goldberg cartoon
Bert