Seeing and Transparency

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

Is it all subjective or are there some guidelines?

It's subjective in that seeing and transparency ratings are based on visual
perception. But there are guidelines and, with experience, a person can very
consistently interpret and apply the scales.

SEEING
The commonly used scales for this are pretty well defined. The two in widest
use are probably the Pickering and Antoniadi scales. Pickering rates seeing
from 1 to 10, with 1 being so bad Sirius' airy disc has an angular diameter
just slightly larger than the Sun ;o) and 10 being perfect. Antoniadi rates
seeing from V (5) to I (1), with I being perfect and V dreary.

Check out this site for an illustrated overview of the Pickering scale:
http://uk.geocities.com/dpeach_78/pickering.htm

Here's a link to a site which discusses the Antoniadi scale:
http://www.npmas.com/resources/seeingtrans.htm

The above site also describes the Tombaugh seeing scale, which is based on the
ability to split circumpolar double stars. Lowell Observatory's Brian Skiff
maintains a list of doubles for seeing checks, he
ftp://ftp.lowell.edu/pub/bas/dbls.fil

TRANSPARENCY
This is a tougher nut to crack. One reason is that people use the term,
differently. A lot of observers use transparency to describe both the darkness
of the sky and the degree of obscurration caused by water vapor, aerosols and
particulates in the air. One common method of quantifying this kind of
transparency is to estimate naked eye limiting magnitude. The Saguaro Astronomy
Club in Phoenix, Arizona, describes their transparency scale, he
http://home.earthlink.net/~tkurkowsk...Learning_to_Se
e/UMi_-_Viewing/SAC_Transparency_Scale.html

Some folks use transparency to describe just the degree of obscuration in the
atmosphere. In this sense, the sky at high noon can be very transparent even
though the limiting magnitude is minus-something-or-other. This useage leaves
darkness as a separate condition of the sky. One scale I've seen rates
transparency based on the color of the sky. The scale goes from 1 to 4, with 4
being perfect:

4=deep blue sky
3=medium blue sky
2=light blue sky
1=pale blue sky

This approach may work well during the day but amateur astronomers need
something which can be applied at ngiht. The SAC scale (see above link) makes
good use of naked eye targets--zodiacal light, gegenschein and Milky Way--which
vary considerably in appearance depending on the degree of atmospheric
transparency.

If you decide to make seeing and transparency estimates as part of your regular
observing routine, clarity and consistency will matter more than the rating
systems you choose. If you're clear about how you're using the terms and
consistent in how you rate those qualities of the sky, then people who read
your observations will be able to get a sense of the observing conditions based
on your ratings.

Regars,

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

Is it all subjective or are there some guidelines?

It's subjective in that seeing and transparency ratings are based on visual
perception. But there are guidelines and, with experience, a person can very
consistently interpret and apply the scales.

SEEING
The commonly used scales for this are pretty well defined. The two in widest
use are probably the Pickering and Antoniadi scales. Pickering rates seeing
from 1 to 10, with 1 being so bad Sirius' airy disc has an angular diameter
just slightly larger than the Sun ;o) and 10 being perfect. Antoniadi rates
seeing from V (5) to I (1), with I being perfect and V dreary.

Check out this site for an illustrated overview of the Pickering scale:
http://uk.geocities.com/dpeach_78/pickering.htm

Here's a link to a site which discusses the Antoniadi scale:
http://www.npmas.com/resources/seeingtrans.htm

The above site also describes the Tombaugh seeing scale, which is based on the
ability to split circumpolar double stars. Lowell Observatory's Brian Skiff
maintains a list of doubles for seeing checks, he
ftp://ftp.lowell.edu/pub/bas/dbls.fil

TRANSPARENCY
This is a tougher nut to crack. One reason is that people use the term,
differently. A lot of observers use transparency to describe both the darkness
of the sky and the degree of obscurration caused by water vapor, aerosols and
particulates in the air. One common method of quantifying this kind of
transparency is to estimate naked eye limiting magnitude. The Saguaro Astronomy
Club in Phoenix, Arizona, describes their transparency scale, he
http://home.earthlink.net/~tkurkowsk...Learning_to_Se
e/UMi_-_Viewing/SAC_Transparency_Scale.html

Some folks use transparency to describe just the degree of obscuration in the
atmosphere. In this sense, the sky at high noon can be very transparent even
though the limiting magnitude is minus-something-or-other. This useage leaves
darkness as a separate condition of the sky. One scale I've seen rates
transparency based on the color of the sky. The scale goes from 1 to 4, with 4
being perfect:

4=deep blue sky
3=medium blue sky
2=light blue sky
1=pale blue sky

This approach may work well during the day but amateur astronomers need
something which can be applied at ngiht. The SAC scale (see above link) makes
good use of naked eye targets--zodiacal light, gegenschein and Milky Way--which
vary considerably in appearance depending on the degree of atmospheric
transparency.

If you decide to make seeing and transparency estimates as part of your regular
observing routine, clarity and consistency will matter more than the rating
systems you choose. If you're clear about how you're using the terms and
consistent in how you rate those qualities of the sky, then people who read
your observations will be able to get a sense of the observing conditions based
on your ratings.

Regars,

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

Is it all subjective or are there some guidelines?

It's subjective in that seeing and transparency ratings are based on visual
perception. But there are guidelines and, with experience, a person can very
consistently interpret and apply the scales.

SEEING
The commonly used scales for this are pretty well defined. The two in widest
use are probably the Pickering and Antoniadi scales. Pickering rates seeing
from 1 to 10, with 1 being so bad Sirius' airy disc has an angular diameter
just slightly larger than the Sun ;o) and 10 being perfect. Antoniadi rates
seeing from V (5) to I (1), with I being perfect and V dreary.

Check out this site for an illustrated overview of the Pickering scale:
http://uk.geocities.com/dpeach_78/pickering.htm

Here's a link to a site which discusses the Antoniadi scale:
http://www.npmas.com/resources/seeingtrans.htm

The above site also describes the Tombaugh seeing scale, which is based on the
ability to split circumpolar double stars. Lowell Observatory's Brian Skiff
maintains a list of doubles for seeing checks, he
ftp://ftp.lowell.edu/pub/bas/dbls.fil

TRANSPARENCY
This is a tougher nut to crack. One reason is that people use the term,
differently. A lot of observers use transparency to describe both the darkness
of the sky and the degree of obscurration caused by water vapor, aerosols and
particulates in the air. One common method of quantifying this kind of
transparency is to estimate naked eye limiting magnitude. The Saguaro Astronomy
Club in Phoenix, Arizona, describes their transparency scale, he
http://home.earthlink.net/~tkurkowsk...Learning_to_Se
e/UMi_-_Viewing/SAC_Transparency_Scale.html

Some folks use transparency to describe just the degree of obscuration in the
atmosphere. In this sense, the sky at high noon can be very transparent even
though the limiting magnitude is minus-something-or-other. This useage leaves
darkness as a separate condition of the sky. One scale I've seen rates
transparency based on the color of the sky. The scale goes from 1 to 4, with 4
being perfect:

4=deep blue sky
3=medium blue sky
2=light blue sky
1=pale blue sky

This approach may work well during the day but amateur astronomers need
something which can be applied at ngiht. The SAC scale (see above link) makes
good use of naked eye targets--zodiacal light, gegenschein and Milky Way--which
vary considerably in appearance depending on the degree of atmospheric
transparency.

If you decide to make seeing and transparency estimates as part of your regular
observing routine, clarity and consistency will matter more than the rating
systems you choose. If you're clear about how you're using the terms and
consistent in how you rate those qualities of the sky, then people who read
your observations will be able to get a sense of the observing conditions based
on your ratings.

Regars,

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

Is it all subjective or are there some guidelines?

It's subjective in that seeing and transparency ratings are based on visual
perception. But there are guidelines and, with experience, a person can very
consistently interpret and apply the scales.

SEEING
The commonly used scales for this are pretty well defined. The two in widest
use are probably the Pickering and Antoniadi scales. Pickering rates seeing
from 1 to 10, with 1 being so bad Sirius' airy disc has an angular diameter
just slightly larger than the Sun ;o) and 10 being perfect. Antoniadi rates
seeing from V (5) to I (1), with I being perfect and V dreary.

Check out this site for an illustrated overview of the Pickering scale:
http://uk.geocities.com/dpeach_78/pickering.htm

Here's a link to a site which discusses the Antoniadi scale:
http://www.npmas.com/resources/seeingtrans.htm

The above site also describes the Tombaugh seeing scale, which is based on the
ability to split circumpolar double stars. Lowell Observatory's Brian Skiff
maintains a list of doubles for seeing checks, he
ftp://ftp.lowell.edu/pub/bas/dbls.fil

TRANSPARENCY
This is a tougher nut to crack. One reason is that people use the term,
differently. A lot of observers use transparency to describe both the darkness
of the sky and the degree of obscurration caused by water vapor, aerosols and
particulates in the air. One common method of quantifying this kind of
transparency is to estimate naked eye limiting magnitude. The Saguaro Astronomy
Club in Phoenix, Arizona, describes their transparency scale, he
http://home.earthlink.net/~tkurkowsk...Learning_to_Se
e/UMi_-_Viewing/SAC_Transparency_Scale.html

Some folks use transparency to describe just the degree of obscuration in the
atmosphere. In this sense, the sky at high noon can be very transparent even
though the limiting magnitude is minus-something-or-other. This useage leaves
darkness as a separate condition of the sky. One scale I've seen rates
transparency based on the color of the sky. The scale goes from 1 to 4, with 4
being perfect:

4=deep blue sky
3=medium blue sky
2=light blue sky
1=pale blue sky

This approach may work well during the day but amateur astronomers need
something which can be applied at ngiht. The SAC scale (see above link) makes
good use of naked eye targets--zodiacal light, gegenschein and Milky Way--which
vary considerably in appearance depending on the degree of atmospheric
transparency.

If you decide to make seeing and transparency estimates as part of your regular
observing routine, clarity and consistency will matter more than the rating
systems you choose. If you're clear about how you're using the terms and
consistent in how you rate those qualities of the sky, then people who read
your observations will be able to get a sense of the observing conditions based
on your ratings.

Regars,

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

Hi Edward,

I use three different scales, one for seeingm one for transparency and
one for sky darkness. I use the Thompson scales. I've got them from a
fellow astronomer, but he doesn't know the origin. Of course there are
other scales you can use. For seeing there is the pickering scale and
for sky darkness the bortle scale. Follow this link to my website:

http://www.backyard-astro.com/Logs/logsreport.html

Read the text on top of the page. There you will find links to the
Pickering and Bortle scales. If you scroll down the page you will find
the three scales I use, numbered from 1 to 10, with all the
descriptions. For me, these scales work fine. I think that it doesn't
matter what scale you use. Important is that you use the same scale for
all your observations. That's my personal opinion.

If you have any more questions about the scales I use, please feel free
to ask.

Best regards,

Math
http://www.backyard-astro.com


Edward Smith wrote:

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

Hi Edward,

I use three different scales, one for seeingm one for transparency and
one for sky darkness. I use the Thompson scales. I've got them from a
fellow astronomer, but he doesn't know the origin. Of course there are
other scales you can use. For seeing there is the pickering scale and
for sky darkness the bortle scale. Follow this link to my website:

http://www.backyard-astro.com/Logs/logsreport.html

Read the text on top of the page. There you will find links to the
Pickering and Bortle scales. If you scroll down the page you will find
the three scales I use, numbered from 1 to 10, with all the
descriptions. For me, these scales work fine. I think that it doesn't
matter what scale you use. Important is that you use the same scale for
all your observations. That's my personal opinion.

If you have any more questions about the scales I use, please feel free
to ask.

Best regards,

Math
http://www.backyard-astro.com


Edward Smith wrote:

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

Hi Edward,

I use three different scales, one for seeingm one for transparency and
one for sky darkness. I use the Thompson scales. I've got them from a
fellow astronomer, but he doesn't know the origin. Of course there are
other scales you can use. For seeing there is the pickering scale and
for sky darkness the bortle scale. Follow this link to my website:

http://www.backyard-astro.com/Logs/logsreport.html

Read the text on top of the page. There you will find links to the
Pickering and Bortle scales. If you scroll down the page you will find
the three scales I use, numbered from 1 to 10, with all the
descriptions. For me, these scales work fine. I think that it doesn't
matter what scale you use. Important is that you use the same scale for
all your observations. That's my personal opinion.

If you have any more questions about the scales I use, please feel free
to ask.

Best regards,

Math
http://www.backyard-astro.com


Edward Smith wrote:

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

Hi Edward,

I use three different scales, one for seeingm one for transparency and
one for sky darkness. I use the Thompson scales. I've got them from a
fellow astronomer, but he doesn't know the origin. Of course there are
other scales you can use. For seeing there is the pickering scale and
for sky darkness the bortle scale. Follow this link to my website:

http://www.backyard-astro.com/Logs/logsreport.html

Read the text on top of the page. There you will find links to the
Pickering and Bortle scales. If you scroll down the page you will find
the three scales I use, numbered from 1 to 10, with all the
descriptions. For me, these scales work fine. I think that it doesn't
matter what scale you use. Important is that you use the same scale for
all your observations. That's my personal opinion.

If you have any more questions about the scales I use, please feel free
to ask.

Best regards,

Math
http://www.backyard-astro.com


Edward Smith wrote:

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

On Fri, 16 Jan 2004 03:18:46 GMT, Edward Smith wrote:

OK. In the astro photography newsgroup, people frequently list both
seeing and transparency at the time of their photos on a 1-10 scale
with 10 being good. I realize that this is somewhat subjective and I
can understand 1 (cloudy for transparency and looking at the horizon
in the sahara at noon in the middle of summer for seeing) and 10
(crystal clear and no distortion at all), but what do the intermediate
numbers mean? Is it all subjective or are there some guidelines?

For seeing, a measure of objectivity is possible by measuring (or at least
estimating) the size of an Airy disc (though Airy blur is more accurate,
with bad seeing). The larger the stellar image, the poorer the seeing.
In smaller instruments, however, the stellar images may jump around
instead of swelling up (as with naked eye vision, which is what causes
twinkling), making the measurement more difficult. It's the same
principle - more movement means worse seeing.

With transparency, something between 1 and 10 means haziness. Basically,
large diffuse cloud cover that's only partiallly transparent. To measure,
I expect that the difference between published apparent magnitude and
actual apparent magnitude of a star can be used to calculate a rating.

I suspect that most people simply assign numbers intuitively, with varying
degrees of accuracy.

--
- Mike

Remove 'spambegone.net' and reverse to send e-mail.