Milky Way Magnitude?

Dear Astronomy Experts
Last night was the clearest in weeks. I even saw the band of stars
comprising the Milky Way, what is the magnitude when it is visible?
Cordially
G. Smith

"ypauls" skrev i melding ...
Last night was the clearest in weeks. I even saw the band of stars
comprising the Milky Way, what is the magnitude when it is visible?

The full moon is mag. -12.5, Sirius the brightest star in the night sky
mag. -1.5, whilst the faintest stars visible to the naked eye under good
conditions are around mag. +6.

"ypauls" skrev i melding ...
Last night was the clearest in weeks. I even saw the band of stars
comprising the Milky Way, what is the magnitude when it is visible?

The full moon is mag. -12.5, Sirius the brightest star in the night sky
mag. -1.5, whilst the faintest stars visible to the naked eye under good
conditions are around mag. +6.

G. Smith wrote:
Last night was the clearest in weeks. I even saw the band of stars
comprising the Milky Way, what is the magnitude when it is visible?

If you're talking about the classical band of milky light encompassing the
celestial sphere, it doesn't make much sense to talk about its integrated
magnitude since only half--at most--of the Milky Way is visible from any
location at any moment in time. Surface brightness is, however, another matter.

The Milky Way has a surface brightness similar to that of any other edge-on
disk galaxy in the sky. Let's take NGC 4565 for example. Its surface brightness
is 21.9 magnitude per square arcsecond. M31 isn't quite edge-on but it is a
grand spiral design, like our home galaxy. M31 has a surface brightness of 22.2
MPSA. The Milky Way is a highly structured object but, on the whole, I'd guess
it has a surface brightness of about 22.0 MPSA.

If you're asking about the brightness of the sky when the Milky Way becomes
visible, that depends on the transparency of the sky. I've seen the Milky Way
through Cassiopeia during a nearly full Moon when the sky surface brightness
would have been about 18.2 MPSA. However, that's from a high elevation site
with excellent transparency. The sky would have to be darker for the Milky Way
to be visible from a sea level site with lower transparency.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
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All I want to know is:
If I can see the Milky Way band, am I looking at mag. 6 or mag. 3 or?
(It was a moonless night last night in Central California...)

"Bill Ferris" wrote in message
...
G. Smith wrote:
Last night was the clearest in weeks. I even saw the band of stars
comprising the Milky Way, what is the magnitude when it is visible?

If you're talking about the classical band of milky light encompassing
the
celestial sphere, it doesn't make much sense to talk about its
integrated
magnitude since only half--at most--of the Milky Way is visible from any
location at any moment in time. Surface brightness is, however, another
matter.

The Milky Way has a surface brightness similar to that of any other
edge-on
disk galaxy in the sky. Let's take NGC 4565 for example. Its surface
brightness
is 21.9 magnitude per square arcsecond. M31 isn't quite edge-on but it
is a
grand spiral design, like our home galaxy. M31 has a surface brightness
of 22.2
MPSA. The Milky Way is a highly structured object but, on the whole, I'd
guess
it has a surface brightness of about 22.0 MPSA.

If you're asking about the brightness of the sky when the Milky Way
becomes
visible, that depends on the transparency of the sky. I've seen the
Milky Way
through Cassiopeia during a nearly full Moon when the sky surface
brightness
would have been about 18.2 MPSA. However, that's from a high elevation
site
with excellent transparency. The sky would have to be darker for the
Milky Way
to be visible from a sea level site with lower transparency.

Regards,

Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
=============
Email: Remove "ic" from .comic above to respond

You asked:

All I want to know is:
If I can see the Milky Way band, am I looking at mag. 6 or mag. 3 or?
(It was a moonless night last night in Central California...)

I think I know what you're after. At my home in Lake Stevens, Washington,
the Milky Way is fairly bright when my overall naked eye limiting magnitude
(NELM) is 5+. However, to my eyes, it is certainly visible when then NELM
is around 4.5. I would say, therefore, that the overall visual magnitude of
the Milky Way is around 4.5. Is this kind of what you want? It may not be
precise, as I am figuring this with recollection only in the middle of the
afternoon, but it is approximate and should give you a way to figure it out
more precisely for your eyes.

Martin

You asked:

All I want to know is:
If I can see the Milky Way band, am I looking at mag. 6 or mag. 3 or?
(It was a moonless night last night in Central California...)

I think I know what you're after. At my home in Lake Stevens, Washington,
the Milky Way is fairly bright when my overall naked eye limiting magnitude
(NELM) is 5+. However, to my eyes, it is certainly visible when then NELM
is around 4.5. I would say, therefore, that the overall visual magnitude of
the Milky Way is around 4.5. Is this kind of what you want? It may not be
precise, as I am figuring this with recollection only in the middle of the
afternoon, but it is approximate and should give you a way to figure it out
more precisely for your eyes.

Martin

"ypauls" wrote in message ...
All I want to know is:
If I can see the Milky Way band, am I looking at mag. 6 or mag. 3 or?
(It was a moonless night last night in Central California...)

When you are looking at the Milky Way band or the night sky,
typically, the Milky Way band first becomes visible, in my experience,
in a mag 5.0 to 6.0 sky.

You may find the International Dark Skies Association "dark sky" scale
helpful in determining the limiting magnitude based on general sky
conditions. It includes references to in what skies the Milky Way band
first becomes visible:

http://www.darksky.org/darksky/index.html

Useful IDSA descriptions discussing the Milky Way band (excerpted from
the above web page) a

5.1 - 5.5 The indistinct Milky Way faintly visible only near the
zenith. Zodiacal light invisible. M31, the Andromeda Galaxy, is barely
discernible.

5.6 - 6.0 The Milky Way is now more easily seen, but lacks detail.
M13, the Great Hercules globular star cluster can now be just glimpsed
when near the zenith. The Zodiacal light is still invisible. The Milky
Way from Auriga through Orion still invisible.

6.1 - 6.5 The Milky Way is now obvious and some detail can be
glimpsed. The Zodiacal light is now barely visible, but not obvious.
The Milky Way from Auriga through Orion is faintly visible. There is
still noticeable skyglow along the horizon due to distant towns and
cities.

An alternative general dark skies scale, the Bortle Dark Sky Scale,
can be found at:

http://skyandtelescope.com/resources...ticle_81_1.asp

Bortle's descriptions for a Bortle Class 5, 4 and 3 skies, referencing
the Milky Way, (excerpted from the above web page), a

Class 5: Suburban sky. Only hints of the zodiacal light are seen on
the best spring and autumn nights. The Milky Way is very weak or
invisible near the horizon and looks rather washed out overhead. Light
sources are evident in most if not all directions. Over most or all of
the sky, clouds are quite noticeably brighter than the sky itself. The
naked-eye limit is around 5.6 to 6.0, and a 32-cm reflector will reach
about magnitude 14.5 to 15.

Class 4: Rural/suburban transition. Fairly obvious light-pollution
domes are apparent over population centers in several directions. The
zodiacal light is clearly evident but doesn't even extend halfway to
the zenith at the beginning or end of twilight. The Milky Way well
above the horizon is still impressive but lacks all but the most
obvious structure. M33 is a difficult averted-vision object and is
detectable only when at an altitude higher than 50 degrees. Clouds in
the direction of light-pollution sources are illuminated but only
slightly so, and are still dark overhead. You can make out your
telescope rather clearly at a distance. The maximum naked-eye limiting
magnitude is 6.1 to 6.5, and a 32-cm reflector used with moderate
magnification will reveal stars of magnitude 15.5.

Class 3: Rural sky. Some indication of light pollution is evident
along the horizon. Clouds may appear faintly illuminated in the
brightest parts of the sky near the horizon but are dark overhead. The
Milky Way still appears complex, and globular clusters such as M4, M5,
M15, and M22 are all distinct naked-eye objects. M33 is easy to see
with averted vision. The zodiacal light is striking in spring and
autumn (when it extends 60 degrees above the horizon after dusk and
before dawn) and its color is at least weakly indicated. Your
telescope is vaguely apparent at a distance of 20 or 30 feet. The
naked-eye limiting magnitude is 6.6 to 7.0, and a 32-cm reflector will
reach to 16th magnitude.

I print and include the above pages in my observing kit for easy
reference in the field.

If you want further information, I can provide you more references to
the systematic approach that amateur astronomers use to estimate
zenithal limiting magnitude and naked eye limiting magnitude on a
particular night.

Regards - Kurt

According to IDSA descriptions:

5.1 - 5.5 The indistinct Milky Way faintly visible only near the
zenith.

I have seen this piece of information before and know that the Milky Way is
visible in brighter skies than a NELM of 5.1. I'll stick to my earlier
response in this thread.


Martin

I suppose you mean "any location from the surface of Earth". From
out in free space, far away from the Earth (yep, those places are
included in "any location"), you can see more than half of the Milky Way.

Paul, you forgot the pedant mode, /pedant mode tags.

Regards,


Bill Ferris
"Cosmic Voyage: The Online Resource for Amateur Astronomers"
URL: http://www.cosmic-voyage.net
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