| |
Main
Date: 04 Nov 2006 21:09:21
From: John Ruddy
Subject: Green Laser Pointer
|
After having seen a couple in action at some recent star parties, I am
interested in purchasing one of these - they seem ideal for pointing
directly at stars and planets to help people locate objects. However, I
am at a loss as to what I am looking for in one - a quick perusal of
ebay shows models from 5mW up to 100mW. Obviously the more powerful one
is, they brighter the beam, and the further it will travel, but I dont
want to go overboard - they seem to increase in price quite rapidly, as
well as being more dangerous!
Can anyone help advise me on this?
|
|
| |
Date: 04 Nov 2006 19:18:46
From: Don't Be Evil
Subject: Re: Green Laser Pointer
|
Dennis Woos wrote:
> "John Ruddy" <john@ruddy2.eclipse.co.uk> wrote in message
> news:eLKdnV_Fp7MenNDYnZ2dnUVZ8tidnZ2d@eclipse.net.uk...
> > After having seen a couple in action at some recent star parties, I am
> > interested in purchasing one of these - they seem ideal for pointing
> > directly at stars and planets to help people locate objects. However, I am
> > at a loss as to what I am looking for in one - a quick perusal of ebay
> > shows models from 5mW up to 100mW. Obviously the more powerful one is,
> > they brighter the beam, and the further it will travel, but I dont want to
> > go overboard - they seem to increase in price quite rapidly, as well as
> > being more dangerous!
> >
> >
> > Can anyone help advise me on this?
>
> You can't go wrong with buying a 5mw green laser from Howie Glatter:
>
> http://www.skypointer.net/
>
> He is a fellow astronomer as well as a manufacturer of laser collimators,
> etc., and is a supporter of astro events.
>
> Dennis
Howie Glatter may be the king of laser collimators, but he advocates
using a laser pointer as a finder. That's just asking for an aircraft
to encounter your beam.
I'm not a member of the anti-laser horde. But, they need to be used
responsibly. They can easily cause permanent eye damage at close
range, and pointing them at aircraft can be a felony.
I do think they're great when carefully used as intended. I use a
powerful flashlight instead since I always have kids around and also
live 10 miles from a major airport. If you don't, the laser is
certainly better.
Greg
|
| | |
Date: 04 Nov 2006 22:53:14
From: Dennis Woos
Subject: Re: Green Laser Pointer
|
> Howie Glatter may be the king of laser collimators, but he advocates
> using a laser pointer as a finder. That's just asking for an aircraft
> to encounter your beam.
There is nothing wrong with using the pointer as a finder - just don't point
it at low-flying airplanes. I guess it depends on where you observe
vis-a-vis flight path, etc. We don't have our pointer mounted on a scope,
but we do use it as a finder. One of us will locate a target in our mounted
binos, and illuminate it with the handheld laser so that we can find it in
our scopes. The binos (9x63, 20x80, and even 7x50) are much better than any
finder we could mount on the scopes.
Dennis
|
| | |
Date: 05 Nov 2006 10:20:26
From: John Ruddy
Subject: Re: Green Laser Pointer
|
Don't Be Evil wrote:
> Howie Glatter may be the king of laser collimators, but he advocates
> using a laser pointer as a finder. That's just asking for an aircraft
> to encounter your beam.
>
> I'm not a member of the anti-laser horde. But, they need to be used
> responsibly. They can easily cause permanent eye damage at close
> range, and pointing them at aircraft can be a felony.
>
I think it may be here in the UK as well. I live in quite a rural area,
the nearest airport is about 15 miles away, and thats what is classed as
a sub-regional one - few night flights and only a million passengers a
year. It should be fairly easy to avoid troubling the local constabulary!
> I do think they're great when carefully used as intended. I use a
> powerful flashlight instead since I always have kids around and also
> live 10 miles from a major airport. If you don't, the laser is
> certainly better.
>
> Greg
>
Having recently moved here, I've discovered that quite a few neighbours
have admired the starry night, but don't know whats what. I thought
using such a pointer may help to identify objects to intereste passers
by, rather than as a finder. My own telescope is an autostar equipped
Meade, so I dont need a finder as much.
|
| | |
Date: 09 Nov 2006 18:14:36
From: Bob G.
Subject: Re: Green Laser Pointer
|
>
>I do think they're great when carefully used as intended. I use a
>powerful flashlight instead since I always have kids around and also
>live 10 miles from a major airport. If you don't, the laser is
>certainly better.
>
>Greg
Yep I live 60 miles away from 3 Major Airports 6-7 miles from a local
one...not really much of a problem....however I live 5 miles from Camp
David and the Pres flies ringht over my house... No need to ask for
trouble by using a Laser in my case...
Bob G.
|
| |
Date: 04 Nov 2006 23:31:31
From: Andy Hewitt
Subject: Re: Green Laser Pointer
|
John Ruddy <john@ruddy2.eclipse.co.uk > wrote:
> After having seen a couple in action at some recent star parties, I am
> interested in purchasing one of these - they seem ideal for pointing
> directly at stars and planets to help people locate objects. However, I
> am at a loss as to what I am looking for in one - a quick perusal of
> ebay shows models from 5mW up to 100mW. Obviously the more powerful one
> is, they brighter the beam, and the further it will travel, but I dont
> want to go overboard - they seem to increase in price quite rapidly, as
> well as being more dangerous!
>
>
> Can anyone help advise me on this?
I got an 8mW one off eBay for about a tenner. I use it to align my Tal1
(I strapped it to the finder scope). You would think it's going all the
way to the stars (in reality it reached about 1500m).
However, before anyone moans, this one does not switch on, I have to
hold the button down to operate. This is Ok, as I only flash it on for a
few seconds to get a rough alignment. Also be aware that using these
near airports can result in a knock at the door.
--
Andy Hewitt
<http://web.mac.com/andrewhewitt1/ >
|
| | |
Date: 06 Nov 2006 21:27:22
From: Mobey Dick
Subject: Re: Green Laser Pointer
|
"Andy Hewitt" <wildrover.andy@googlemail.com > wrote in message
news:1hoax59.51all81kwkoowN%wildrover.andy@googlemail.com...
> John Ruddy <john@ruddy2.eclipse.co.uk> wrote:
>
>> After having seen a couple in action at some recent star parties, I am
>> interested in purchasing one of these - they seem ideal for pointing
>> directly at stars and planets to help people locate objects. However, I
>> am at a loss as to what I am looking for in one - a quick perusal of
>> ebay shows models from 5mW up to 100mW. Obviously the more powerful one
>> is, they brighter the beam, and the further it will travel, but I dont
>> want to go overboard - they seem to increase in price quite rapidly, as
>> well as being more dangerous!
>>
>>
>> Can anyone help advise me on this?
>
> I got an 8mW one off eBay for about a tenner. I use it to align my Tal1
> (I strapped it to the finder scope). You would think it's going all the
> way to the stars (in reality it reached about 1500m).
>
> However, before anyone moans, this one does not switch on, I have to
> hold the button down to operate. This is Ok, as I only flash it on for a
> few seconds to get a rough alignment. Also be aware that using these
> near airports can result in a knock at the door.
>
> --
> Andy Hewitt
> <http://web.mac.com/andrewhewitt1/>
Actually, it is going all the way to the stars (a photon or two are, anyway)
|
| | | |
Date: 06 Nov 2006 13:36:24
From: Mij Adyaw
Subject: Re: Green Laser Pointer
|
>> Andy Hewitt
>> <http://web.mac.com/andrewhewitt1/>
>
> Actually, it is going all the way to the stars (a photon or two are,
> anyway)
>
Is that really true? I am not sure that any light from the pointer will make
it out into space. I just isn't powerful enough.
|
| | | | |
Date: 07 Nov 2006 04:50:48
From: Sam Wormley
Subject: Re: Green Laser Pointer
|
Mij Adyaw wrote:
>
> Is that really true? I am not sure that any light from the pointer will make
> it out into space. I just isn't powerful enough.
>
>
Unless the light gets absorbed it just keeps going no matter how weak!
|
| | | | | |
Date: 07 Nov 2006 11:16:22
From: TeaTime
Subject: Re: Green Laser Pointer
|
"Sam Wormley" <swormley1@mchsi.com > wrote in message
news:IgU3h.227152$FQ1.59356@attbi_s71...
> Mij Adyaw wrote:
>>
>> Is that really true? I am not sure that any light from the pointer will
>> make it out into space. I just isn't powerful enough.
>>
>>
>
> Unless the light gets absorbed it just keeps going no matter how weak!
>
Quite so. I should have thought the fact we can use telescopes to see light
that left distant stars thousands of millions of years ago would speak for
the longevity of light photons. A single photon of green light of a given
wavelength has the same quantum energy as any similar one, regardless of
whether it originated from a giant star or a hand-held pointer.
For those geeky enough to want the math:
According to Planck's hypothesis, for your green laser pointer, photon
energy E = hC/L where:
h is Planck's constant 6.626 x 10^-34 Joule.sec
C is speed of light 2.99729458 x 10^8 metres/sec
L is the wavelength 5.32 x 10^-7 metres
yielding E = 3.733 x 10^-19 Joules which is 0.0000000000000000003733
Joules
(and a Joule is how much energy is required to run a 1 Watt lightbulb for
one second)
yet they still travel through space for billions of years and just keep on
going ... amazing innit.
|
| | | | | | |
Date: 07 Nov 2006 14:28:50
From: Sam Wormley
Subject: Re: Green Laser Pointer
|
TeaTime wrote:
> "Sam Wormley" <swormley1@mchsi.com> wrote in message
> news:IgU3h.227152$FQ1.59356@attbi_s71...
>> Mij Adyaw wrote:
>>> Is that really true? I am not sure that any light from the pointer will
>>> make it out into space. I just isn't powerful enough.
>>>
>>>
>> Unless the light gets absorbed it just keeps going no matter how weak!
>>
>
> Quite so. I should have thought the fact we can use telescopes to see light
> that left distant stars thousands of millions of years ago would speak for
> the longevity of light photons. A single photon of green light of a given
> wavelength has the same quantum energy as any similar one, regardless of
> whether it originated from a giant star or a hand-held pointer.
>
> For those geeky enough to want the math:
>
> According to Planck's hypothesis, for your green laser pointer, photon
> energy E = hC/L where:
>
> h is Planck's constant 6.626 x 10^-34 Joule.sec
> C is speed of light 2.99729458 x 10^8 metres/sec
> L is the wavelength 5.32 x 10^-7 metres
>
> yielding E = 3.733 x 10^-19 Joules which is 0.0000000000000000003733
> Joules
> (and a Joule is how much energy is required to run a 1 Watt lightbulb for
> one second)
>
> yet they still travel through space for billions of years and just keep on
> going ... amazing innit.
>
>
With a TV set and an antenna, one can detect CMB photons that originated
13.7 billion years ago.
|
| | | | | | | |
Date: 07 Nov 2006 16:40:53
From: TeaTime
Subject: Re: Green Laser Pointer
|
"Sam Wormley" <swormley1@mchsi.com > wrote in message
news:CK04h.136413$aJ.107098@attbi_s21...
> With a TV set and an antenna, one can detect CMB photons that originated
> 13.7 billion years ago.
Oh yes, about 1% of the background noise picked up by a satellite dish is
attributable to the Cosmic Microwave Background. Having a black-body
temperature of just 2.73 above absolute zero and with wavelengths in
millimetres rather than Angstroms, their feeble photon energy is perhaps
1/4000 of that of green light, yet they are the oldest and longest travelled
beasties we can currently detect. Any more bids?
|
| | | | | | | | |
Date: 07 Nov 2006 17:13:20
From: Paul Schlyter
Subject: Re: Green Laser Pointer
|
In article <pG24h.14890$163.862@newsfe6-gui.ntli.net >,
TeaTime <licknsticker@hotmail.com > wrote:
>
>"Sam Wormley" <swormley1@mchsi.com> wrote in message
>news:CK04h.136413$aJ.107098@attbi_s21...
>> With a TV set and an antenna, one can detect CMB photons that originated
>> 13.7 billion years ago.
>
>Oh yes, about 1% of the background noise picked up by a satellite dish is
>attributable to the Cosmic Microwave Background. Having a black-body
>temperature of just 2.73 above absolute zero and with wavelengths in
>millimetres rather than Angstroms, their feeble photon energy is perhaps
>1/4000 of that of green light, yet they are the oldest and longest travelled
>beasties we can currently detect. Any more bids?
It's more like 1/2000 of that of green light.
Wien's displacement law says that the peak wavelength of the Planckian
blackbody radiation is inversely proportional to the blackbody temperature.
The Sun has its peak near green light, and the surface temperature
of the Sun is some 6000 K
6000 / 2.73 = approx. 2200
The peak wavelength of the 2.73 K background radiation is some 1.2 mm
--
----------------------------------------------------------------
Paul Schlyter, Grev Turegatan 40, SE-114 38 Stockholm, SWEDEN
e-mail: pausch at stockholm dot bostream dot se
WWW: http://stjarnhimlen.se/
|
| | | | | | | | | |
Date: 07 Nov 2006 17:54:35
From: TeaTime
Subject: Re: Green Laser Pointer
|
"Paul Schlyter" <pausch@saaf.se > wrote in message
news:eiqe64$1aug$1@merope.saaf.se...
> It's more like 1/2000 of that of green light.
>
> Wien's displacement law says that the peak wavelength of the Planckian
> blackbody radiation is inversely proportional to the blackbody
> temperature.
>
> The Sun has its peak near green light, and the surface temperature
> of the Sun is some 6000 K
>
> 6000 / 2.73 = approx. 2200
>
> The peak wavelength of the 2.73 K background radiation is some 1.2 mm
Yes, inverted wavelength arithmetic on my part. I was mentally dividing 1.2
by 5600 instead of 560nm by 1200000nm. Still pretty feeble by anyone's
reckoning (bit like me really) :))
|
| | | | | | |
Date: 07 Nov 2006 11:23:39
From: TeaTime
Subject: Re: Green Laser Pointer
|
... and it has been shown that the dark-accustomed and healthy human eye can
actually detect single photons, with sensitivity peaking in the green
wavelengths. Remarkable.
|
| | | | | | | |
Date: 07 Nov 2006 17:28:00
From: lal_truckee
Subject: Re: Green Laser Pointer
|
TeaTime wrote:
> ... and it has been shown that the dark-accustomed and healthy human eye can
> actually detect single photons, with sensitivity peaking in the green
> wavelengths. Remarkable.
References, please...
|
| | | | | | | | |
Date: 07 Nov 2006 17:41:39
From: TeaTime
Subject: Re: Green Laser Pointer
|
"lal_truckee" <lal_truckee@yahoo.com > wrote in message
news:Am34h.6$GS2.3@newssvr14.news.prodigy.com...
> TeaTime wrote:
>> ... and it has been shown that the dark-accustomed and healthy human eye
>> can actually detect single photons, with sensitivity peaking in the green
>> wavelengths. Remarkable.
>
> References, please...
Just one of many:
http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html
(see 'Rod Details')
|
| | | | | | | | |
Date: 07 Nov 2006 19:53:14
From: Ioannis
Subject: Re: Green Laser Pointer
|
"lal_truckee" <lal_truckee@yahoo.com > wrote in message
news:Am34h.6$GS2.3@newssvr14.news.prodigy.com...
>
> TeaTime wrote:
> > ... and it has been shown that the dark-accustomed and healthy human eye
can
> > actually detect single photons, with sensitivity peaking in the green
> > wavelengths. Remarkable.
>
> References, please...
I think it's pretty standard stuff on most intro Nuclear Physics books. For
example, the spinthariscope, invented by Sir William Crookes in 1903, had the
capability of generating individual photons, which were detectable by the eye.
http://en.wikipedia.org/wiki/Spinthariscope
The alpha particles from Ra that fall on the zinc sulfide screen, generate a
single photon and the eye is able to pereceive the tiny flash through the
little eyepiece.
--
Ioannis
-------
Every man has his price. Mine is $3.95.
|
| | | | | | | | |
Date: 09 Nov 2006 16:02:09
From: Llanzlan Klazmon the 15th
Subject: Re: Green Laser Pointer
|
lal_truckee <lal_truckee@yahoo.com > wrote in
news:Am34h.6$GS2.3@newssvr14.news.prodigy.com:
> TeaTime wrote:
>> ... and it has been shown that the dark-accustomed and healthy human
>> eye can actually detect single photons, with sensitivity peaking in the
>> green wavelengths. Remarkable.
>
> References, please...
That is pretty standard stuff. Fully dark adapted rod cells can respond to
a single photon. On the average though, about seven to ten photons have to
hit before the rod cell fires. However the visual processing system doesn't
normally register a single rod cell firing. Several adjacent rods usually
have to fire before the visual system responds. For this reason night
vision is of lower resolution than day vision. The overall quantum
efficiency of the dark adapted human visual system is probably around one
percent.
Kalzmon
http://en.wikipedia.org/wiki/Rod_cells
|
| | | | |
Date: 06 Nov 2006 21:45:10
From: Fleetie
Subject: Re: Green Laser Pointer
|
> Is that really true? I am not sure that any light from the pointer will make it out into space. I just isn't powerful enough.
Of course it's true. Not every photon will be absorbed by the atmospehere.
It's true that you'll never be able to see the spot from a green
(oor any other colour) laser pointer on the Moon; even with the powerful
pulsed lasers that they aim at the retroreflector arrays on the Moon,
they collect on average less than ONE photon per outgoing pulse.
With a hand-held green laser pointer you'll see NOTHING. But that's more
of a divergence issue.
Some photons will be absorbed, I guess, and others will be Rayleigh-scattered
out of the intended direction of the beam as they propagate through the
atmosphere.
Yes, photons from your green laser pointer will make it to "space" if
you point it into the sky. What percentage I'm not sure, but it's non-zero.
Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie
|
| | | | | |
Date: 06 Nov 2006 21:55:45
From: Fleetie
Subject: Re: Green Laser Pointer
|
> Yes, photons from your green laser pointer will make it to "space" if
> you point it into the sky. What percentage I'm not sure, but it's non-zero.
I should add that photons from your candle flame or your mobile phone
backlight will also make into space. It's just a matter of number of
photons per second, or percentage of those emitted from the source.
There's nothing special in this respect about photons from a laser
pointer.
Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.livejournal.com/userinfo.bml?user=fleetie
|
| | | | | | |
Date: 06 Nov 2006 22:29:24
From: Andy Hewitt
Subject: Re: Green Laser Pointer
|
Fleetie <fleetie@fleetie.demon.co.uk > wrote:
> > Yes, photons from your green laser pointer will make it to "space" if
> > you point it into the sky. What percentage I'm not sure, but it's non-zero.
>
> I should add that photons from your candle flame or your mobile phone
> backlight will also make into space. It's just a matter of number of
> photons per second, or percentage of those emitted from the source.
>
> There's nothing special in this respect about photons from a laser
> pointer.
This argument is somewhat pointless I would think. This is like saying
'you can see a grain of sand on a beach from space' - providing you have
the equipment to do so.
Surely a single photon of light is just going to be lost on all the
other light photons that are scattered around the atmosphere. From a
practical sense, it would be impractical, if not impossible, to detect
it.
--
Andy Hewitt
<http://web.mac.com/andrewhewitt1/ >
|
| | | | | | | |
Date: 07 Nov 2006 12:24:39
From: Llanzlan Klazmon the 15th
Subject: Re: Green Laser Pointer
|
wildrover.andy@googlemail.com (Andy Hewitt) wrote in
news:1hoejf7.19y23yp1vsxh57N%wildrover.andy@googlemail.com:
> Fleetie <fleetie@fleetie.demon.co.uk> wrote:
>
>> > Yes, photons from your green laser pointer will make it to "space" if
>> > you point it into the sky. What percentage I'm not sure, but it's
>> > non-zero.
>>
>> I should add that photons from your candle flame or your mobile phone
>> backlight will also make into space. It's just a matter of number of
>> photons per second, or percentage of those emitted from the source.
>>
>> There's nothing special in this respect about photons from a laser
>> pointer.
>
> This argument is somewhat pointless I would think. This is like saying
> 'you can see a grain of sand on a beach from space' - providing you have
> the equipment to do so.
>
> Surely a single photon of light is just going to be lost on all the
> other light photons that are scattered around the atmosphere. From a
> practical sense, it would be impractical, if not impossible, to detect
> it.
Relatively few photons percent wise from a green laser pointer pointed
straight up on a clear night get scattered. That is what is meant by the
atmosphere being transparent. I couldn't find a free article giving the
measured figures but reading off the graphs of wavelength versus
transmission I could find, the atmosphere appears to have better than 98%
transmission for green light, clouds permitting. Of course detection is a
different issue caused by divergence of the beam.
Klazmon.
>
|
| |
Date: 04 Nov 2006 17:46:31
From: Dennis Woos
Subject: Re: Green Laser Pointer
|
"John Ruddy" <john@ruddy2.eclipse.co.uk > wrote in message
news:eLKdnV_Fp7MenNDYnZ2dnUVZ8tidnZ2d@eclipse.net.uk...
> After having seen a couple in action at some recent star parties, I am
> interested in purchasing one of these - they seem ideal for pointing
> directly at stars and planets to help people locate objects. However, I am
> at a loss as to what I am looking for in one - a quick perusal of ebay
> shows models from 5mW up to 100mW. Obviously the more powerful one is,
> they brighter the beam, and the further it will travel, but I dont want to
> go overboard - they seem to increase in price quite rapidly, as well as
> being more dangerous!
>
>
> Can anyone help advise me on this?
You can't go wrong with buying a 5mw green laser from Howie Glatter:
http://www.skypointer.net/
He is a fellow astronomer as well as a manufacturer of laser collimators,
etc., and is a supporter of astro events.
Dennis
|
| |
Date: 04 Nov 2006 15:42:14
From: Shawn
Subject: Re: Green Laser Pointer
|
John Ruddy wrote:
> After having seen a couple in action at some recent star parties, I am
> interested in purchasing one of these - they seem ideal for pointing
> directly at stars and planets to help people locate objects. However, I
> am at a loss as to what I am looking for in one - a quick perusal of
> ebay shows models from 5mW up to 100mW. Obviously the more powerful one
> is, they brighter the beam, and the further it will travel, but I dont
> want to go overboard - they seem to increase in price quite rapidly, as
> well as being more dangerous!
>
>
> Can anyone help advise me on this?
5 mW or less lasers have no licensing requirement (in the U.S. anyway).
They work great for showing things to people standing conversationally
close to the user. Good ones can be purchased for less than $100 U.S.
I like mine and find it very useful when observing with small groups.
Make sure you know the GLP policy of any big star party you attend.
There are some militant anti-laser types out there. Just watch where
this thread goes to see what I mean. :-)
Shawn
|
| | |
Date: 04 Nov 2006 22:59:12
From: Proginoskes
Subject: Re: Galileo (NOT Einstein) is inventor of Second postulate of Relativity
|
AJAY SHARMA wrote:
> Galileo (NOT Einstein) is inventor of Second postulate of Relativity [...]
And you just found this out?
Next time, pay attention in class.
--- Christopher Heckman
|
| |
Date: 05 Nov 2006 10:50:18
From: callisto
Subject: Re: Green Laser Pointer
|
Several comments on Green Laser Pointers:
I use GLPs for small "star parties" of neighbors or just another
person. They are great for pointing out individual stars, no matter
how faint and for outlining constellations. In addition I use GLPs for
finders on my telescopes. I have standard finders but rarely need to
use them.
I think the problems of GLPs ruining the images obtained by
astrophotographers have been greatly exaggerated. I would be
interested in knowing how many of these photographers have actually had
their pictures corrupted by GLPs.
It is true that more and more sky parties, especially the larger ones,
are banning them. Some even kick you out if you turn one on during
nighttime hours. It's a shame that they couldn't set up fields a
short distance from the main observing field for use by people who want
to use GLPs.
Someone mentioned Howie Glatter as a good source for these pointers. I
will back that up - I have three from him. He also makes brackets so
you can mount the GLP on your telescope.
All or most GLPs do not have an on-off switch and you must keep a
constant pressure on the GLP button for it to work. You can get around
this by using a common wooden clothespin or a small rubber "O" ring
that will slide over the button and thus free up your hand.
I have never had any problems with airplanes or helicopters. At night
they all have lights so you can just wait until they leave the section
of the sky you are interested in.
GLPs can definitely harm a person's eye but I think most people are
overly concerned about this. Just use common sense and keep the GLPs
out of the hands of kids. There is an interesting article about the
effects of GLPs from the Mayo Clinic. The researcher doing the study
states, "This is a potential hazard to people's eyes, but rarely is it
going to be a practical hazard because the aversion reflex we have
naturally will cause a person to blink or turn away from a laser
light." The complete press release can be found at
http://www.mayoclinic.org/news2005-rst/2800.html
Although I obviously like GLPs, I have found one negative thing about
them. When you are showing people locations of stars, DSOs etc, I find
that many, especially kids, are more interested in the GLP than in
astronomy
|
| | |
Date: 05 Nov 2006 19:23:51
From: Florian
Subject: Re: Green Laser Pointer
|
>Although I obviously like GLPs, I have found one negative thing about
>them. When you are showing people locations of stars, DSOs etc, I find
>that many, especially kids, are more interested in the GLP than in
>astronomy
Haha! How true. I use a GLP finder on my Tele Vue 76 and find it works =
great.=20
I also pretty much always observe alone so there is never a problem
of the light bothering anyone else. But the times i've used the pointer=20
to show someone something in the night sky they always want to play=20
with the laser... ;-)
.Florian
|
| |
Date: 05 Nov 2006 10:42:55
From: callisto
Subject: Re: Green Laser Pointer
|
John Ruddy wrote:
> Don't Be Evil wrote:
>
> > Howie Glatter may be the king of laser collimators, but he advocates
> > using a laser pointer as a finder. That's just asking for an aircraft
> > to encounter your beam.
> >
> > I'm not a member of the anti-laser horde. But, they need to be used
> > responsibly. They can easily cause permanent eye damage at close
> > range, and pointing them at aircraft can be a felony.
> >
>
> I think it may be here in the UK as well. I live in quite a rural area,
> the nearest airport is about 15 miles away, and thats what is classed as
> a sub-regional one - few night flights and only a million passengers a
> year. It should be fairly easy to avoid troubling the local constabulary!
>
>
> > I do think they're great when carefully used as intended. I use a
> > powerful flashlight instead since I always have kids around and also
> > live 10 miles from a major airport. If you don't, the laser is
> > certainly better.
> >
> > Greg
> >
>
>
> Having recently moved here, I've discovered that quite a few neighbours
> have admired the starry night, but don't know whats what. I thought
> using such a pointer may help to identify objects to intereste passers
> by, rather than as a finder. My own telescope is an autostar equipped
> Meade, so I dont need a finder as much.
|
| |
Date: 08 Nov 2006 19:06:00
From: Jonathan Silverlight
Subject: Re: Green Laser Pointer
|
In message <aWZ3h.4404$YA3.1493@newsfe7-win.ntli.net >, TeaTime
<licknsticker@hotmail.com > writes
>
>"Sam Wormley" <swormley1@mchsi.com> wrote in message
>news:IgU3h.227152$FQ1.59356@attbi_s71...
>> Mij Adyaw wrote:
>>>
>>> Is that really true? I am not sure that any light from the pointer will
>>> make it out into space. I just isn't powerful enough.
>>>
>>>
>>
>> Unless the light gets absorbed it just keeps going no matter how weak!
>>
>
>Quite so. I should have thought the fact we can use telescopes to see light
>that left distant stars thousands of millions of years ago would speak for
>the longevity of light photons.
Isn't their longevity zero? :-) From the viewpoint of a photon time does
not pass.
The oldest photons I've consciously seen (in my frame) are 2 thousand
million years old (from 3C273). Not bad for a small reflector in
suburban London, though I suspect people her can do better.
|
| | |
Date: 09 Nov 2006 02:13:40
From: TeaTime
Subject: Re: Green Laser Pointer
|
"Jonathan Silverlight" <jsilverlight@spam.merseia.fsnet.co.uk.invalid > wrote
in message news:OYITS6ZpjiUFFwOI@ntlworld.com...
> In message <aWZ3h.4404$YA3.1493@newsfe7-win.ntli.net> Isn't their
> longevity zero? :-) From the viewpoint of a photon time does not pass.
>Isn't their longevity zero? :-) From the viewpoint of a photon time does
>not pass.
That's a philosophical poimt, Jonathan! Isn't longevity, like beauty, in
the eye of the beholder?
|
| |
Date: 11 Nov 2006 05:44:50
From: Rune Allnor
Subject: Re: Green Laser Pointer
|
Fleetie skrev:
> > Is that really true? I am not sure that any light from the pointer will make it out into space. I just isn't powerful enough.
...
> Some photons will be absorbed, I guess, and others will be Rayleigh-scattered
> out of the intended direction of the beam as they propagate through the
> atmosphere.
I would imagine the scattering of the photons in the atmosthere
is the whole clue behind the GLP, isn't it? Somehow, the photons
(or at least the energy, depending on the scattering mechanisms)
that leave the laser needs to be dispersed back to reach the
eyes of the observers.
Rune
|
| | |
Date: 11 Nov 2006 15:58:14
From: Chris L Peterson
Subject: Re: Green Laser Pointer
|
On 11 Nov 2006 05:44:50 -0800, "Rune Allnor" <allnor@tele.ntnu.no >
wrote:
>I would imagine the scattering of the photons in the atmosthere
>is the whole clue behind the GLP, isn't it? Somehow, the photons
>(or at least the energy, depending on the scattering mechanisms)
>that leave the laser needs to be dispersed back to reach the
>eyes of the observers.
Of course, what you see is scattered light from the laser. But that
doesn't change the fact that only a small fraction of the light is
scattered when a GLP is pointed straight up. Most of the beam's energy
will escape the atmosphere, and could be detected very easily in space
from a low Earth orbit- probably even visually.
_________________________________________________
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
|
| |
Date: 17 Dec 2006 19:13:12
From: Jonathan Silverlight
Subject: Re: Green Laser Pointer
|
In message <b9pbl25drpviefbhnk3mjfoc14pbnhnih2@4ax.com >, Chris L
Peterson <clp@alumni.caltech.edu > writes
>On 11 Nov 2006 05:44:50 -0800, "Rune Allnor" <allnor@tele.ntnu.no>
>wrote:
>
>Of course, what you see is scattered light from the laser. But that
>doesn't change the fact that only a small fraction of the light is
>scattered when a GLP is pointed straight up. Most of the beam's energy
>will escape the atmosphere, and could be detected very easily in space
>from a low Earth orbit- probably even visually.
A 2 watt argon laser was imaged by Surveyor 7 on the Moon in 1968
<http://www.w7ftt.net/laser2.html >
That's a fairly impressive bit of kit, but I wonder what a dark-adapted
human eye could see, especially with modest optical aid.
|
|
