Discovery of PLuto ...

Mike Dworetsky writes:

Charon is more than two magnitudes fainter than Pluto.

That depends on the wavelength. In visible light, Charon is 5.5 times
fainter than Pluto. That's less than two magnitudes.

wrote:

Mike Dworetsky writes:

Charon is more than two magnitudes fainter than Pluto.

That depends on the wavelength. In visible light, Charon is 5.5 times
fainter than Pluto. That's less than two magnitudes.

For what value of PLuto's albedo ?

wnowak writes:

Mike Dworetsky writes:

Charon is more than two magnitudes fainter than Pluto.

That depends on the wavelength. In visible light, Charon is 5.5 times
fainter than Pluto. That's less than two magnitudes.

For what value of PLuto's albedo ?

Pluto's albedo is a strong function of both rotational phase and
wavelength.

wrote:

wnowak writes:

Mike Dworetsky writes:

Charon is more than two magnitudes fainter than Pluto.

That depends on the wavelength. In visible light, Charon is 5.5 times
fainter than Pluto. That's less than two magnitudes.

For what value of PLuto's albedo ?

Pluto's albedo is a strong function of both rotational phase and
wavelength.

My point is that in 1950 the polar regions of PLuto were visible from the
Earth, that are
more reflective as far as I know. So, in spite of the fact that PLuto was
fainter, the relative difference of brightness
between two objects could have been above 2 mag. making it a bit more
difficult to discover a moon.

Also, please remember that PLuto was farther so the max. angular distance was
.... let me calculate ... .
~ 0.74 arsec ? If these guys were not lucky, and observed at min. angular
distance then it takes us down to ...
~ 0.66 * 0.74 = 0.49 ! This is probably just a bit too little. Once I have
time, I will use HORIZONS again to verify
for the date of 21st of March 1950, or maybe somebody else is interested in
doing this.
Any volunteers ?

In article ,
"Mike Dworetsky" writes:
If you do a search on the ADS you will find Kuiper's paper in the 1950 Publs
of the Astr Soc Pacific, v. 62, p133.

Thanks, Mike. A few salient quotes:

"fine seeing, about 6 on a scale of 10." Hard to know what this
means. If I had to guess, I might put it at about 0.9 arcsec FWHM.
But this is just a guess.

The observation was made 1950 March 22, 4h UT. Anybody care to
calculate the separation of Pluto and Charon at that time? Kuiper
gives Pluto's distance as 35.56 AU. Is the modern value any
different? Kuiper also gives a zenith distance of 20 degrees. Is
that consistent with the time of observation?

The angular diameter was found to be 0.23
arcsec (0.20 if some corrections were taken into account).

With the modern Pluto diameter of 1195 km and Kuiper's distance, the
correct value should have been 0.046 arcsec (if I've done the
calculation right).

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
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Steve Willner writes:

Mike Dworetsky writes:

If you do a search on the ADS you will find Kuiper's paper in the 1950 Publs
of the Astr Soc Pacific, v. 62, p133.

Thanks, Mike. A few salient quotes:

"fine seeing, about 6 on a scale of 10." Hard to know what this
means. If I had to guess, I might put it at about 0.9 arcsec FWHM.
But this is just a guess.

The observation was made 1950 March 22, 4h UT. Anybody care to
calculate the separation of Pluto and Charon at that time?

I did so once a long time ago, when this same topic was being
discussed. As I recall, the value didn't lead to any conclusive
result, but I don't remember the exact value. Extrapolating an
orbit with a few year arc back for over 30 years is going to
have some uncertainty associated with it. Perhaps after I get a
chance to do a global solution with data spanning nearly two
decades, an extrapolation to 1950 can be regarded as fairly
certain.

Kuiper
gives Pluto's distance as 35.56 AU. Is the modern value any
different?

It's close enough.

Kuiper also gives a zenith distance of 20 degrees. Is
that consistent with the time of observation?

Yes.

The angular diameter was found to be 0.23
arcsec (0.20 if some corrections were taken into account).

With the modern Pluto diameter of 1195 km and Kuiper's distance, the
correct value should have been 0.046 arcsec (if I've done the
calculation right).

Radius, not diameter. And 1195 is too big. Probably no smaller
than 1150, however.

With the modern Pluto diameter of 1195 km and Kuiper's distance, the
correct value should have been 0.046 arcsec (if I've done the
calculation right).

In article ,
writes:
Radius, not diameter. And 1195 is too big. Probably no smaller
than 1150, however.

Argh! Yes, radius. Thanks, Dave. (You can tell who is the expert
and who just looks things up in AQ.) So call it 0.09 arcsec true
diameter against Kuiper's claimed 0.20 arcsec. Not bad, really,
considering the difficulties of the measurement.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)

Steve Willner writes:

With the modern Pluto diameter of 1195 km and Kuiper's distance, the
correct value should have been 0.046 arcsec (if I've done the
calculation right).

Radius, not diameter. And 1195 is too big. Probably no smaller
than 1150, however.

Argh! Yes, radius. Thanks, Dave. (You can tell who is the expert
and who just looks things up in AQ.) So call it 0.09 arcsec true
diameter against Kuiper's claimed 0.20 arcsec. Not bad, really,
considering the difficulties of the measurement.

Some of the earliest speckle measurements of the diameter also came
out too large. I recall values of 3000 and 4000 km being published,
with some model dependency due to the assumed amount of limb
darkening.

In article ,
wnowak writes:
Excellent seeing in California in 1930-50 would be 0.30 arcsec. right ?

Seeing that good would would be exceptional even at Mt. Wilson, and
Palomar on the whole is a bit worse than Mt. Wilson. A quick web
search turns up a cookbook for one of the CCD cameras at Palomar.
According to the author, "The seeing at Palomar is typically ~1.0 to
1.5 arcseconds FWHM, sometimes as good as 0.8 to 0.9 arcseconds."
That accords with my own memory from the 1970's.

See also http://www.chara.gsu.edu/CHARA/Reports/tr13.pdf , which
cites reports that the seeing is seasonally dependent. My guess
would be that March is probably around average.

A more thorough search may turn up other reports.

--
Steve Willner Phone 617-495-7123
Cambridge, MA 02138 USA
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement. Commercial
email may be sent to your ISP.)