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Science Forum Index » Astro - Amateur Forum » Beginner's Observing Suggestions - for familes, children, an
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| Dave Jessie |
 Posted: Thu Feb 15, 2007 10:44 pm |
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Regina Roper wrote:
Quote: For People Who Like to Read Beginner-Level Astronomy Articles:
Hi again, Regina,
I do believe I've found an error very near the beginning of your webpage
that reads as follows:
"Our UNAIDED human eye can see very far away and back many years in time.
The Andromeda galaxy (Messier No. 31, or "M31"), which observers can just
perceive as a faint smudge of light in a very dark sky, is about 13.2
TRILLION miles away (its light arrived here 2.2 million years after leaving
the stars of the galaxy!)"
I believe what you should have there is:
"Our UNAIDED human eye can see very far away and back many years in time.
The Andromeda galaxy (Messier No. 31, or "M31"), which observers can just
perceive as a faint smudge of light in a very dark sky, is about 13.2
QUINTILLION miles away (its light arrived here 2.2 million years after
leaving the stars of the galaxy!)"
You're off by about 10^6 ;^)
Check it out. 1 ly is about 6 trillion miles (9 trillion km) so 2.2 million
ly is WAY more than 13.2 trillion miles.
Clear Dark Steady Skies,
Dave Jessie |
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| Regina Roper |
| Posted: Mon Feb 19, 2007 2:42 pm |
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On Thu, 15 Feb 2007 21:44:05 -0500, "Dave Jessie"
<DJesSHOESsie@neo.rr.com> wrote:
Quote: Regina Roper wrote:
For People Who Like to Read Beginner-Level Astronomy Articles:
Hi again, Regina,
I do believe I've found an error...
I believe what you should have there is:
"Our UNAIDED human eye can see very far away and back many years in time.
The Andromeda galaxy (Messier No. 31, or "M31"), which observers can just
perceive as a faint smudge of light in a very dark sky, is about 13.2
QUINTILLION miles away (its light arrived here 2.2 million years after
leaving the stars of the galaxy!)"
You're off by about 10^6 ;^)
Check it out. 1 ly is about 6 trillion miles (9 trillion km) so 2.2 million
ly is WAY more than 13.2 trillion miles.
Clear Dark Steady Skies,
Dave Jessie
I think I can intuit how that mistake was made.
I used a javascript calculator online to convert ly to miles and when
I entered 2.2 million ly, it output that number. Going back to it
again to double check, it came out with the same number. WRONG!
Today I tried a different calculator and came up with
12,932,975,821,003,938,792,240.2932975821003938e+22.
I tried a third calculator and came up with:
1.29326996 × 10 to the 19th
A fourth calculator yielded:
1.292670807453416e+22 Miles
A fifth calculator choked up and registered "NaN"
A sixth calculator output:
11473502371152.47 (no exponent)
A seventh calculator yielded:
1.292412368e+22 mile
So, when we did this a long time ago, it is apparent that the
calculator we used did not work correctly; it is also apparent that
the ones on the web NOW aren't always right, either.
Sorry. I'll get the correct figure in the page. Thanks.
RR |
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| Regina Roper |
| Posted: Mon Feb 19, 2007 2:54 pm |
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On Thu, 15 Feb 2007 16:12:57 -0700, W. H. Greer <sendnomail@tome.net>
wrote:
Quote: One final, minor point that looks to be in need of correction:
In (3) under "(C) CLEANING EYEPIECES" it looks to me like the phrase
"outer surface of the eye lens" should be changed to read: "outer
surface of the field lens".
I'm not sure that it is actually wrong. Yes: the field lens surface
can be in focus. But in some of our eyepieces, any speck of dust on
the outer eye lens is clearly in focus; on others the dust is
inconsequential. I can remember having to clean and clean to be able
to look at the Moon without all kinds of sharply focused little bits
and pieces.
RR |
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| Regina Roper |
| Posted: Mon Feb 19, 2007 3:08 pm |
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On Thu, 15 Feb 2007 16:12:57 -0700, W. H. Greer <sendnomail@tome.net>
wrote:
Quote: Related Contextual Note:
My first 'real' telescope had one eyepiece. It was a Ramsden
eyepiece. The outer surface of the Ramsden's field lens was
coincident with the eyepiece/telescope focal plane. As a result, any
speck of dust, tiny living organism, etc. that was present on the
outer surface of that lens was silhouetted in perfect focus against
the lunar landforms when I was observing the Moon. It was
particularly entertaining when a tiny, live, moving spider was on that
lens during a lunar observation 
My husband Stephen says that his Edmund 6" reflector came with three
Ramsden eyepieces, the last of which he threw away only a few years
ago. When he got the beat-up telescope from somebody who had stored
it in an attic, he found a dead spider in the "1 inch" ocular, which
-- as you say -- showed up *in focus* when he looked thru it!
I have done some corrections to the page and have credited you and
Dave at the end for your suggestions -- thanks.
RR |
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