Lowest magnitude possible?

I seem to recall a formula that gives the lowest magnitude for apertures
of diameter D, as log something, from the FAQ. (I kept the formula on my
second HD, but two nights ago it crashed and I lost it. If somebody has
it handy, please post it).

There is an apparent paradox he

With my 60mm/700mm Tasco, I was able to discern M57, but barely, from
Antiparos. I had to use averted vision, but when I did, the nebula was
clearly visible. No smoke ring, no nothing. Just a blur, but it was
there.

Now, "Turn left at Orion", mentions M57 as having an overall magnitude
of 9.3 (if memory serves right?)

The fact that it's 9.x and it's a nebula, means that it's luminosity is
spread out, so individual parts of it should have even less brightness
than 9.3. It is, however, visible.

On the other hand, my Tasco cannot show Polaris' companion, listed as
magnitude 9, even though theoretically (I don't remember the $#%&
formula) Polaris B should be within the D=60 limit and the separation is
clearly doable.

I saw it with my neighbour's Meade ETX 125 EC, but with the Tasco, no
way.

What gives? How can the Tasco show M57 and not Polaris B?

Thanks for any enlightment.

Happy observing as always!
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

The formula gives you a very conservative number, Ioannis.
How dim you can see greatly depends on the condition of your
sky (i.e. light pollution, transparency), your visual acruity and
experience. Here's my favorite article about how dim you can
see.
http://www.efn.org/~mbartels/aa/visual.html

M57 is actually very bright, much brighter than its mag 9 may
suggest, high surface brightness that is. Here's a sketch of M57
from a 60mm and according to my research, M57 can be seen
as ring with a 60mm refractor providing you use high magnification
(more than 100x).
http://astrosurf.com/l60/en/L60_deep_sky.html

As yourseeing companion of Polaris, the 60mm should be able
to reach between mag 11-12. Because the companion is much
dimmer than the primary which is mag 2.1, it could be difficult to
see at low power. But it's a wide double (18" sepaaration); so
it should be hard to split. What magnification did you try?

Ron B[ee]
-----------
"Ioannis" wrote in message
...
I seem to recall a formula that gives the lowest magnitude for apertures
of diameter D, as log something, from the FAQ. (I kept the formula on my
second HD, but two nights ago it crashed and I lost it. If somebody has
it handy, please post it).

There is an apparent paradox he

With my 60mm/700mm Tasco, I was able to discern M57, but barely, from
Antiparos. I had to use averted vision, but when I did, the nebula was
clearly visible. No smoke ring, no nothing. Just a blur, but it was
there.

Now, "Turn left at Orion", mentions M57 as having an overall magnitude
of 9.3 (if memory serves right?)

The fact that it's 9.x and it's a nebula, means that it's luminosity is
spread out, so individual parts of it should have even less brightness
than 9.3. It is, however, visible.

On the other hand, my Tasco cannot show Polaris' companion, listed as
magnitude 9, even though theoretically (I don't remember the $#%&
formula) Polaris B should be within the D=60 limit and the separation is
clearly doable.

I saw it with my neighbour's Meade ETX 125 EC, but with the Tasco, no
way.

What gives? How can the Tasco show M57 and not Polaris B?

Thanks for any enlightment.

Happy observing as always!
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

Ron B[ee] wrote:

The formula gives you a very conservative number, Ioannis.
How dim you can see greatly depends on the condition of your
sky (i.e. light pollution, transparency), your visual acruity and
experience. Here's my favorite article about how dim you can
see.
http://www.efn.org/~mbartels/aa/visual.html

Many thanks. This page has been bookmarked :*)

M57 is actually very bright, much brighter than its mag 9 may
suggest, high surface brightness that is. Here's a sketch of M57
from a 60mm and according to my research, M57 can be seen
as ring with a 60mm refractor providing you use high magnification
(more than 100x).
http://astrosurf.com/l60/en/L60_deep_sky.html

Hmmm. Not even close for a low mag. The picture suggests direct vision,
but I was able to see it only using averted. Perhaps with averted vision
and high mag what the webpage shows is possible, but I only remember
that the surface brightness dropped off suddently. That is, the
boundaries of M57 were sharply defined, but I did not see any central
details, such as a dropping in brightness towards the central region.
Something was definately there, but with the Tasco I wasn't able to say
"what".

And we are talking 6+ skies, with me being able to count 7 Pleiades
naked eye, after 1 hour of dark adaptation. Seems to me that the
webpage's sketch is a bit on the optimistic side.

Perhaps the magnification I used for M57 (x40) was too low.

As yourseeing companion of Polaris, the 60mm should be able
to reach between mag 11-12. Because the companion is much
dimmer than the primary which is mag 2.1, it could be difficult to
see at low power. But it's a wide double (18" sepaaration); so
it should be hard to split. What magnification did you try?

For Polaris, x116. For M57, around x40.

Ron B[ee]

Happy observing!

-----------
"Ioannis" wrote in message
...
[snip]
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

Magnification isn't always the answer. I have little trouble seeing M-57
as a 'ring' at only 20 magnifications, but with 5" binoculars. It's
tiny, but clearly has a dark center. You do have to know what you're
looking for, however.

Dan Mitchell
==========

Ioannis wrote:

Ron B[ee] wrote:

The formula gives you a very conservative number, Ioannis.
How dim you can see greatly depends on the condition of your
sky (i.e. light pollution, transparency), your visual acruity and
experience. Here's my favorite article about how dim you can
see.
http://www.efn.org/~mbartels/aa/visual.html

Many thanks. This page has been bookmarked :*)

M57 is actually very bright, much brighter than its mag 9 may
suggest, high surface brightness that is. Here's a sketch of M57
from a 60mm and according to my research, M57 can be seen
as ring with a 60mm refractor providing you use high magnification
(more than 100x).
http://astrosurf.com/l60/en/L60_deep_sky.html

Hmmm. Not even close for a low mag. The picture suggests direct vision,
but I was able to see it only using averted. Perhaps with averted vision
and high mag what the webpage shows is possible, but I only remember
that the surface brightness dropped off suddently. That is, the
boundaries of M57 were sharply defined, but I did not see any central
details, such as a dropping in brightness towards the central region.
Something was definately there, but with the Tasco I wasn't able to say
"what".

And we are talking 6+ skies, with me being able to count 7 Pleiades
naked eye, after 1 hour of dark adaptation. Seems to me that the
webpage's sketch is a bit on the optimistic side.

Perhaps the magnification I used for M57 (x40) was too low.

As yourseeing companion of Polaris, the 60mm should be able
to reach between mag 11-12. Because the companion is much
dimmer than the primary which is mag 2.1, it could be difficult to
see at low power. But it's a wide double (18" sepaaration); so
it should be hard to split. What magnification did you try?

For Polaris, x116. For M57, around x40.

Ron B[ee]

Happy observing!

-----------
"Ioannis" wrote in message
...
[snip]
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

9.0 + 5*log(a)

where a = aperture in inches


This formula is too conservative.

The implication in several statements was that the magnification (40X?)
was too low to see M-57 as a ring. This is clearly NOT true. The quote
you provide is far more specific, limiting the statement to conditions
regarding the original poster's 60 mm telescope. It may well be true
that with marginal RESOLUTION (from only 60 mm aperture) more
magnification helps ... in THAT instance.

And, yes, considering the size of the object (M-57) I can easily believe
it's near star like in 11X80's. It can be ( and is) seen as a ring with
20X however, provided ample resolution and contrast go with it. It does
take a little effort and some observing experience to note that it's a
tiny ring, however.

Dan Mitchell
==========

Ioannis wrote:

Daniel A. Mitchell wrote:

Magnification isn't always the answer.

I never said it was. Ron said it and only with respect to this
particular object. Pay attention to what's written in the thread please:

Ron B[ee] wrote:

M57 is actually very bright, much brighter than its mag 9 may
suggest, high surface brightness that is. Here's a sketch of M57
from a 60mm and according to my research, M57 can be seen
as ring with a 60mm refractor providing you use high magnification
(more than 100x).

Daniel A. Mitchell wrote:

I have little trouble seeing M-57
as a 'ring' at only 20 magnifications, but with 5" binoculars. It's
tiny, but clearly has a dark center. You do have to know what you're
looking for, however.

Agreed. I have no trouble seeing it as a hazy star with my 11x80 as
well, but had I not known it's location, I would still think it was a
star of sorts.

Dan Mitchell
==========
[snip]
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

Daniel A. Mitchell wrote:

Magnification isn't always the answer.

I never said it was. Ron said it and only with respect to this
particular object. Pay attention to what's written in the thread please:

Ron B[ee] wrote:

M57 is actually very bright, much brighter than its mag 9 may
suggest, high surface brightness that is. Here's a sketch of M57
from a 60mm and according to my research, M57 can be seen
as ring with a 60mm refractor providing you use high magnification
(more than 100x).

Daniel A. Mitchell wrote:

I have little trouble seeing M-57
as a 'ring' at only 20 magnifications, but with 5" binoculars. It's
tiny, but clearly has a dark center. You do have to know what you're
looking for, however.

Agreed. I have no trouble seeing it as a hazy star with my 11x80 as
well, but had I not known it's location, I would still think it was a
star of sorts.

Dan Mitchell
==========
[snip]
--
Ioannis
http://users.forthnet.gr/ath/jgal/
___________________________________________
Eventually, _everything_ is understandable.

Hi there. You posted:

I seem to recall a formula that gives the lowest magnitude for apertures
of diameter D, as log something, from the FAQ. (I kept the formula on my
second HD, but two nights ago it crashed and I lost it. If somebody has
it handy, please post it).

Most formulae give only a *very* rough idea of the limiting magnitude for
stars which a telescope will go to. The simplest "general" form is m = k +
5*log(d) where d is the effective aperture (inches) of the telescope and k is
some empirical constant which often ranges from 8.5 to possibly as faint as
10.5, depending on who you ask. On a reasonably good night, I have reached
around 15.1 using my 10 inch Newtonian, although on some nights which I deem
fairly good, I might have trouble getting to even 14.7 and on others I might
just barely glimse stars into the low 15's. Even with some calibration of the
formula, the limiting magnitude which you personally might see could easily
differ from what the formula yields. It will depend on the quality of the
sky, the magnification used, and the experience of the observer. Plugging in
a number like 10.1 for k using my 10 inch yields a limit of about 15.1, yet
using my 80mm f/5 "short tube", I have glimsed the 13th magnitude star which
sits next to the Ring Nebula, which would thus yield a k constant of 10.5.
Thus, simple formulae like this might be accurate to at best +/- 0.5
magnitudes and their results should be taken with a large grain of salt.

There is an apparent paradox he

With my 60mm/700mm Tasco, I was able to discern M57, but barely, from
Antiparos. I had to use averted vision, but when I did, the nebula was
clearly visible. No smoke ring, no nothing. Just a blur, but it was
there.

My old notes from over 30 years ago when I first located M57 with my first
telescope (a 2.4 inch refractor like yours) also indicated I could see the
object with averted vision at 35x but not its shape. However, once I started
kicking the power up to around 70x to 100x, I could just glimse the
ring-shape. After years of experience using averted vision, proper dark
adaptation, and power selection, I can see the ring shape with a 60mm aperture
scope at only 50x. It still isn't very bright, but it is fairly obvious (I
have seen the object as a faint point of light in only a pair of 10x50
binoculars).

Now, "Turn left at Orion", mentions M57 as having an overall magnitude
of 9.3 (if memory serves right?)

The exact magnitudes of many planetary nebulae are approximate only (some are
photographic magnitudes). Most of my sources for M57 list a magnitude of 8.8
(visual) and 9.7 (photographic). However, remember that this object is not a
point source like a star, so its surface brightness is much less than its
total magnitude.

On the other hand, my Tasco cannot show Polaris' companion, listed as
magnitude 9, even though theoretically (I don't remember the $#%&
formula) Polaris B should be within the D=60 limit and the separation is
clearly doable.

I saw it with my neighbour's Meade ETX 125 EC, but with the Tasco, no
way.

What gives? How can the Tasco show M57 and not Polaris B?

Polaris B is about 17.8 arc seconds away from Polaris A, and that (plus the
brightness of Polaris itself) may be enough to extinguish the fainter
companion unless higher power is used. If it is not visible at something over
50x, then the scope itself just might not have enough quality, although again,
I suspect that its there but you just aren't noticing it. Good luck and clear
skies to you.

--
David W. Knisely
Prairie Astronomy Club: http://www.prairieastronomyclub.org
Hyde Memorial Observatory: http://www.hydeobservatory.info/

**********************************************
* Attend the 11th Annual NEBRASKA STAR PARTY *
* July 18-23, 2004, Merritt Reservoir *
* http://www.NebraskaStarParty.org *
**********************************************

Ioannis wrote:



What gives? How can the Tasco show M57 and not Polaris B?

Thanks for any enlightment.

Happy observing as always!

Because your Tasco is pointed near zenith when viewing M57, and pointing
elsewhere (unless you live at the north pole) when viewing Polaris B.

Warmest regards,

Etok


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On Tue, 14 Oct 2003 14:56:58 +0200, Ioannis wrote:

I seem to recall a formula that gives the lowest magnitude for apertures
of diameter D, as log something, from the FAQ. (I kept the formula on my
second HD, but two nights ago it crashed and I lost it. If somebody has
it handy, please post it).

There is an apparent paradox he

With my 60mm/700mm Tasco, I was able to discern M57, but barely, from
Antiparos. I had to use averted vision, but when I did, the nebula was
clearly visible. No smoke ring, no nothing. Just a blur, but it was
there.

Now, "Turn left at Orion", mentions M57 as having an overall magnitude
of 9.3 (if memory serves right?)

The fact that it's 9.x and it's a nebula, means that it's luminosity is
spread out, so individual parts of it should have even less brightness
than 9.3. It is, however, visible.

On the other hand, my Tasco cannot show Polaris' companion, listed as
magnitude 9, even though theoretically (I don't remember the $#%&
formula) Polaris B should be within the D=60 limit and the separation is
clearly doable.

I saw it with my neighbour's Meade ETX 125 EC, but with the Tasco, no
way.

What gives? How can the Tasco show M57 and not Polaris B?

Thanks for any enlightment.

Happy observing as always!

If you remove your eyepiece and look down
through the diagonal at the objective, can you
see all of the objective without moving your
head around? A lot of these scopes were
designed to be actually about 50mm instead
of 60mm as advertised. Another problem is
the lack of optical coatings on the diagonal
and the eyepieces. This reduces both the
contrast and light transmission. You can
move the baffle, but with the scope I had
this only reduced the sharpness as the
edges of the objective were apparently
not that good... (Jason brand telescope)

You can often "improve" these telescopes
by buying a "hybrid diagonal" from Orion.
These are .965" where it goes into the
focusing tube, and 1.25" for the eyepiece.
There will be a bit of "cut off" when using
25mm or longer eyepieces, but shorter
1.25" eyepieces will generally work OK.

A good "60" will show quite a bit. The
biggest handicap is probably the .965
two element uncoated "cheapo" H type
eye pieces. Buy a hybrid diagonal, and
order a set of 1.25" Plossls from someone
like "Hands on Optics" (reasonable price,
good quality, I have two, happy with both)

I did a lot of observing for years with just
a pair of 10x50 binoculars and a Meade
220 50mm refractor. The Moon got most
of the time, of course, but small telescopes
can often show a lot more than we'd think!
I have a photo of the Moon on my web page
taken with the Meade and a Canon A10
digital camera. Nothing "fancy", but it
shows that you can see quite a bit with
just simple, low cost equipment...

Clear skies and happy observing!

Jerome Bigge
Member, Muskegon Astronomical Society
Author of the "Warlady" & "Wartime" series.
Download at "http://members.tripod.com/~jbigge"