Boyce, P. B.

English

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ti
l	 Ar LC.^WELL OBSERVATORY
BULLETIN NO. 146
4
VOL. ViI
	 SEPTEIiB ER 4, VXK FLAGSTAFF, ARIZONA	 NO. !)
AIM Rejectid PRELIMINARY OBSERVATIONS OF THEJOVIAN 6190A METHANE BAND
Peter B. Boyce	 tt/	 0 3 -- 0 0 3^ O O
i.owc! ^110bservatOT^
4
P'
a
b
ABSTRACT
Photoelectric .,pec •trtun scans of small areas of
the Jovian sm-face were t ► tade (Im-iug the spring of
1968. A c •omimter program coutp ►► ted the e(lttiva-
lcttt width c ► f the 6190)k methane band b y compar-
ing the scans to similar scans of the ► iron. The
resulting; mean error- of it single detertnin0i0u of
the equivalent width is 2 perc •cttt. The average
e(luivalcnt width at the center of the disk was
16.9A. however, a clay to (lay variation of op to 2A
in the equivalent width was fom ► cl. The equivalent
width also increased with distance from the center
of the disk.
INTRODUCTION
As emphasized by Hess (1953) knowledge of the
distribution of methane across the disk of Jupiter
can icad to it determination of the amount of
methane above the refiec • ting cloud laver which can
in turn be used to estituate a variation i ►► height of
the cloud layer. Earl y investigation of this problem
(e.g., Elvey and Fairley, 1932) showed only it small
variation across the disk of Jupiter. To check these
results, Hess (1953) determined the equivalent
width of the 6190A band of' methane at several
points on the disc of Jupiter. i le concluded that the
equivalent width decreased toward the poles which
he attributed to an increase in the height of the
visible cloud layer. Urey (1959) quotes Dollfus as
not being able to confirm Hess' results. In addition,
Urey remarks upon the difficulty of sustaining the
temperature changes required by Hess' theory.
Consequently, it seemed appropriate to reexamine
this question with modern instrumentation which
shotdd vichl higher accuracies in the dctcrntinatiott
of the cgni yalcnt width.
OBSERVATIONAL TECHNIQUE
The Lowcll spectnim sc •anm c r• was list-(] m ► ;ht-
72 - inch Perkins reflector of' the ( Ohioo Statc allot
(Ohio Wcslc yan Observatories at the Lowell Obser-
vatory to obtain sl)t-ctral sc -uts of Jupiter and the
► noon. A s ystct ► t of D.C. auttplification and voltage-
to-frt-qucncv c •ou ycrsion \yas ust'd to digitize the
signal which was then rccordcd in a 1(NN)-cham ► el
tuultiscaler. 'I'll(- contcuts of the ntnitiscaler were
pmichcd on paper talk for subse(luent redtictio ►►
by it computer.
The spectral scans covered the region from 6(NN)A
to 65(N)A with it resolution of 9A. The photomulti-
plier was an EA1R 541-11 with it tetra-alkali cathode
and was kept at it c•onstcutt temperature of —20 °C
by iut-ans of it thermoelcoric cooler. The scan
spccd was 180A /mill. awl the ir ► tegratiou time was
0.2 so.conds during which the exit slit was mov^-d
1.25A. Each scan took approximately 3 ittirtutes :o
contplctt-.
A rotted focal-plane aperture 5.8 seconds of arc
in diameter was used for all the observations. Posi-
tioning and guiding were accomplished by visually
centering the image of Jupiter and using an offset
guider to maintain the centering during the course
of a scan. On(- of the outer satellites of Jupiter was
used as a guide star. The image was rccentered
after cac •h scan to correct for motion of the satel-
lite relative to the planet. The guiding and position-
ing accuracy is estimated to be 1.5 seconds of are
(max. error) at the center of the disk and somewhat
poorer at other positions.
\T ?-1,
(ACCESSION UM R)
(PA
	 )
(NASA CR OR TMX OR A NUMdE )
;r <^3 0
(THRU)
(CODE)
(CATEGORY)
I
8 93
JUPITER
Methane Band
April 27,1968
Eq. Width= 16.8	 04 4 3 U.T.
6
Rl 1^ 1L.H
JUPITER
May 27, 1968
JOVIAN METHANE BAND
A 619 0
Lowell Spectrum Scanner
p^ = 8 A
6100 A
	 I	 16200A	 I	 1 6300 A
Fig. 1. A spectrum scan of the center of the Jovian disk shown normalized to the standard moon scan. The regions XX6045-
6120A and Xa62M-6360A were used to determine nonnalizing fat'tOrs.
1.00
.95
i
' c .90
.+85
.80
6100 A	 6200A	 6300A
Wavelength
Fig. 2. Positions at which the ,nethane band equivalent width was measured. Ratio of measured equivalent widths to equiva-
lent %vidth at center of disk is given for each position.
94
r
I
i
JUPITER
METHANE BAND S1
X 6190
APRIL-MAY, 1968
Et•
t.
.i
r
N
w
TA111.1•
DATE 1,C\1 1.c:\I I•:iluk .
1968 VA'. S%-Stem 1 tivac m 11 \1 ulth Position
Apr. 27 11.132 100" 166 ' 16.7A Centered
0140 105 171 16.5 W'S sou! I i
01 16 109 174 16.4 678 lout l c
0-159 117 182 16.9 (elitcred
0513 125 1W 18.9 11'.'3.-;ist On sky)
Apr. 28 t111ti 2.19 :307 17.7 Cc•ntc•red
Apr. 29 01:311 056 106 15.7 Centered
0442 062 112 1.4.9 9'.'2 curt I i
0506 077 12`i 16.2 Ccntc•red
0515 082 132 17.2 9"8 north
0521 086 1:36 18.9 1276 north
May 7 0253 178 16; 17.2 Ccntc n—d
Mav 27 11329 115 :312 16.6 Centered
0:337 119 316 17.4 Centered
Jun.	 2 0-108 (NY' 156 17.6 Centered
0417 010 161 17.1 Centered
•
S
Fig. :3. M( thane band profile. Solar continuum has been subtracted out.
95
01
t
	
1.2	 Variation Of X6190
Jovian Methane
W	 Band	 N
CENT	 Vs.
Radial Distance
	
1.1	 E
N
Sec (:)
	
1.0
	 S	 April 27,29,1968
N
DARK H.
BELT
0.9 M
0 12	 14 16 Is 110 112 114	 116
Distance From Center	 (Sec Of Arc
Fig. 4. Variation of equivalent width of X6190A methane band as a function of distance from the sub-earth point. Each point
represents one measurement except at a radius of 6.8 sec. which is an average of two measurements. Error bars denote esti-
mated mean errors. The solid line denotes a variation proportional to the secant of the angle from the sub-earth point.
Sirlilar scans were obtained of the moon at vary- malized to the moon scan at both ends of the
ing zenith distances on three nights. Since there methane band A.X6045-6120A and XX6285••6360A.
were no systematic differences between the differ- Finally, the total area between the two scans in the
ent scans of the moon they were averaged into one range U6120••6285A was determined and normal-
standard moon scan. ized to the average of the two continuum regions
In an effort to be as objective as possible all to give the equivalent width of the methane band.
reduction of the data was handled by a computer A normalized scan of Jupiter is shown with theprogram. After reading in the data for a single scan
average moon scan in Figure 1. Figure _2 shows athe program determined the approximate wave-
length
	
between the Jovian and lunar scans.. match point-by-point. plot of differences between the scans
The wavelength match was checked: by trial and resulting in a profile of the methane absorption
error by maximizing the product moment correla_ band. There was no significant change in the shape
tion coefficient in the wavelength range 6285-6360A of the methane band during the course of the
which contains several strong solar features. As a observations although two scans had been obviously
result the scans were matched in wavelength with distorted by the _occurrence of clouds during the
an accuracy of ±0.6A. The Jovian scan was nor- observations and were discarded.
96
t.
r
t
A
t6
OBSERVATIONAL RESULTS
Table I lists the observational results including
date and time of beginning of scan, local central
meridian of Jupiter in. System I, and II, the derived
equivalent width and the position of the aperture
on the disk of Jupiter. The average mean error as
determined from pairs of observations made on the
same day is less than 0.25A or 2 percent of the
equivalent width. Using this estimate of the error
the observed differences in the strength of the
methane band at the center of the disk are cer-
tainly real (formal confidence level greater than
0,97). However, there are not nearly enough data to
determine whether the variation is simply secular
or is a function of LCM and surface activity on the
planet or both.
Observations' were obtained at several different
points on fhe disk on the nights of April 27 and 29.
Figure 3 depicts the positions of the aperture with
relation to the major dark bands on the disk of
Jupiter. Also included are the ratios of the equiva-
lent widths with respect to the value at the center
of the disk. The photograph from which the sketch
of the surface features was made was taken on
April 28 at 0401 U.T. at New Mexico State Univer-
sity. There is a definite trend for the band strength
to increase with increasing distance from the center
of the disk. Figure 4 is a plot of the band strength
as a function of the radial distance from the center
of the disk. The solid line gives the secant of the
angle from the sub-earth point. This plot does not
take into account any possible variations due to the
differential rotation of Jupiter. Nevertheless, the
increase with radial distance is very marked. The
valuesmarked "dark band" refer to observations in
which a portion of the aperture
.
 covered a dark
belt. On the basis of only two observations the evi-
dence points to a weakening of the methane band
in the dark belts. Further observations will be
needed to substantiate this.
In comparing this work with that of Hess (1953)
who found a marginally significant decrease in
band strength with radial distance it should be
noted that the total observed variation recorded
here is contained within Hess' quoted mean error.
CONCLUSION
This study has shown that the 6v3 band of
methane at 6190A on Jupiter undergoes variations
which are statistically significant. It can be stated
tentatively that the band strength increases toward
the limb of the planet and also shows variations
either with time or position on the planet or both.
Finally, the methane band appears slightly weaker
over the dark belts than over the bright areas.
ACKNOWLEDGMENTS
It is a pleasure to acknowledge the able assist-
ance of Norman C, Crowfoot, who wrote the com-
puter programs and assisted in the reductions of
the observations. The question of the methane band
variability was originally called to my attention by
Stuart E. Jones of the Lowell Observatory Plane-
tary Research Center staff. Computer time and
some of the observational equipment used in this
study were furnished by NASA Grant NsG-451.
Thanks are also due to Bradford Smith of New
Mexico State University for so quickly providing
the necessary photographs of Jupiter.
REFERENCES
Elvey, C. T. and Fairley, A. S. 1932, Ap. J., 75, 373.
Hess, S. L. 1953, Ap. J., 118, 151.
Urey, H. C. 1959, Handbueh d. Physik, 52, 363.
97


Preliminary Observations of the Jovian 6190A Methane Band

Photoelectric spectrum of Jovian 6190A methane ban

General Disclaimer 
One or more of the Following Statements may affect this Document 
 
 This document has been reproduced from the best copy furnished by the 
organizational source. It is being released in the interest of making available as 
much information as possible. 
 
 This document may contain data, which exceeds the sheet parameters. It was 
furnished in this condition by the organizational source and is the best copy 
available. 
 
 This document may contain tone-on-tone or color graphs, charts and/or pictures, 
which have been reproduced in black and white. 
 
 This document is paginated as submitted by the original source. 
 
 Portions of this document are not fully legible due to the historical nature of some 
of the material. However, it is the best reproduction available from the original 
submission. 
 
 
 
 
 
 
 
Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19690001260 2020-03-12T06:17:27+00:00Z
KLOWELL OBSERVATORY
BULLETIN NO. 146
VOL. VII
	 SEPTEMBER 4,196% FLAGSTAFF, ARIZONA
	
NO. 9
PRELIMINARY OBSERVATIONS OF THE
JOVIAN 6190A METHANE BAND
Peter B. Boyce
Lowell Observatory
ABSTRACT
Photoelectric spectrum scans of small areas of
the Jovian surface were made during the spring of
1988. A computer program computed the equiva-
lent width of the 6190A methane band by compar-
ing the scans to similar scans of the moon. The
resulting mean error of a single determination of
the equivalent width is 2 percent. The average
equivalent width at the center of the disk was
18.9A. However, a day to day variation of up to 2A
in the equivalent width was found. The equivalent
width also increased with distance from the center
of the disk.
INTRODUCTION
As emphasized by Hess (1953) knowledge of the
distribution of methane across the disk of Jupiter
can lead to a determination of the amount of
methane above the reflecting cloud layer which can
in turn be used to estimate a variation in height of
the cloud layer. Early investigation, of this problem
(e.g., Elvey and Fairley, 1932) showed only a small
variation across the disk of Jupiter. To check these
results, Hess (1953) determined the equivalent
width of the 6190A band of methane at several
points on the disc of Jupiter. He concluded that the
equivalent width decreased toward the poles which
he attributed to an increase in the height of the
visible cloud layer. Urey (1959) quotes Dollfus as
not being able to confirm Hess' results. In addition,
i~i i C: remarks upon the difficulty of sustaining the
temperature changes required by Hess' theory.
Consequently, it seemed appropriate to reexamine
this question with modern instrumentation which
should yield higher accuracies In the determination
of the equivalent width.
OBSERVATIONAL TECHNIQUE
The Lowell spectrum ;canner was used on the
72-inch Perkins reflector of ^ ^ Ohio State and
Ohio Wesleyan Observatories at the Lowell Obser-
vatory to obtain spectral scans of Jupiter and the
moon. A system of D.C. amplification and voltage-
to-frequencyconversion was used to digitize the
signal which was then recorded in a 1000-channel
multiscaler. The contents of the multiscaler were
punched on paper tape for sui^sequent reduction
by a computer.
The spectral scans covered the region from 6000A
to 6500A with a resolution of 9A. The photomulti-
plier was an EMR 541-R with a tetra-alkali cathode
and was kept at a constant temperature of —200C
by means of a thermoelectric cooler. The scan
speed was 180A/min. and the integration time was
0.2 seconds during which the exit slit was moved
1.25A. Each scan took approximately 3 minutes to
complete.
A round focal-plane aperture 5.8 seconds of arc
in diameter was used for all the observations. Posi-
tioning and guiding were accomplished by visually
centering the image of Jupiter and using an offset
guider to maintain the centering during the course
of a scan. One of the outer satellites of Jupiter was
used as a guide star. The image was recentered
after each scan to correct for motion of the satel-
lite relative to the planet. The guiding and position-
ing accuracy is estimated to be 1.5 seconds of are
(max. error) at the center of the disk and somewhat
poorer at other positions.
(CA1,'EOORY)
10 591
"^^N ER	 (TMRU)
(NASA  CR OR211A Z4 7MX OR AD UMBER)
93
Q i
I^
c 9
.85
.80
JUPITER
Methane Band
April 27,1968
04 4 3 U.T.Eq. Width=16.8
F	 -	 -^
mood
V vLTER
May 27,1968
JOVIAN METHANE BAND
A6190
Lowell Spectrum Scanner
p„A = d A
6100 A
	
6100 A	 16300 A
Fig. 1. A spectrum scan of the center of the jovian disk shown normalized to the standard moon scan. The regions Xa8045-
6120A and NN6285-6360A were used to determine normalizing factors.
...	 .,, .................................................................................................................a ........ A 	 ... .
	 - ........
6100 A	 6200 A	 6300
Wavelength
Fig. 2. Positions at which the methane band equivalent width was measured. Ratio of measured equivalent widths to equiva-
lent width at center of disk is given for each position.
94
rTABLE
DATE 1.(.'NI LCNI I"(luK.
1968 t'.'I'. sy%tem 1 Sy"41cm 11 Width Position
Apr. 27 1432 10) 166, 16,7A Centered
1440 105 171 16.5 6"'s south
0446 IN 174 16.4 6"8 south
04541 11? 182 16.9 Centered
0513 125 190 18.9 11 "  s east ( in sky)
Apr. 28 1418 249 307 17.7 Centered
Apr. 20 0430 056 106 15.7 Centered
0442 062 112 14.9 9':'2 north
0506 077 127 1.6.2 Centered
0515 082 132 17.2 9'.'8 north
0521 086 136 18.9 12'.'6 north
May 7 0253 178 167 17.2 Centered
May 27 0329 115 312 16.6 Centered
0337 110 316 17.4 Centered
Jul).	 2 0408 005 156 17.6 Centered
0417 010 161 17.1 Centered
JUPITER	 N
METHANE BAND STRENGTH
X 6190	 1.19
APR I! - MAY, 1968
W
.98
S
Fig. 3. Methane band profile. Solar continuum has been subtracted out.
05
1.2	 Variation Of X6190
Jovion Methane
+NW7W7	 B
WCINT
Rod iol Distance
1.1	 E
N
Sec
1.0 S
	
April 27, 29,
1968
N
DARK
0.9 r
	
BELT
0	 12	 14	 16	 Is	 110	 112	 114	 18
Di:tanco From C= (Sec Of Arc)
Fig. 4. Variation of equivalent width of X6190A methane brand as a function of distance from the sub-earth point. Each point
represents one measurement except at a radius of 6.8 sec. which is an average of two measurements. Error bars denote esti-
mated mean errors. The solid line denotes it variation proportional to the secant of the angle from the sub-earth point.
Similar scans were obtained of the moon at vary-
ing zenith distances on three nights. Since there
were no systematic differences between the differ-
ent scans of the moon they were averaged into one
standard moon scan.
In an effort to be as objective as possible all
reduction of the data was handled by a computer
program. After reading in the data for a single scan
the program determined the approximate wave-
length match between the Jovian and lunar scans.
The wavelength match was checked by trial and
error by maximizing the product moment correla-
tion coefficient in the wavelength range 6285-6360A
which contains several strong solar features. As a
result the scans were matched in wavelength with
an accuracy of ±OAA. The Jovian scan was nor••
malized io the moon scan at Loth ends of the
methane band AX6045-6120A and AA6285-6360A.
Finally, the total area between the two scans in the
range A46120-6285A was determined and normal-
ized to the average of the two continuum regions
to give the equivalent width of the methane band.
A normalized scan of Jupiter is shown with the
average moon scan in Figure 1. Figure 2 shows a
point-by-point plot of differences between the scans
resulting in a profile of the methane absorption
band. There was no significant change in the shape
of the methane band during the course of the
observations although two scans had been obviously
distorted by the occurrence of clouds during the
observations and were discarded.
96
_
OBSERVATIONAL RESULTS
`fable 1 lists the observational results including
date and time of beginning of scan, local central
meridian of Jupiter in .ivstent 1, and 11, the derived
equivalent width and the position of the aperture
oil disk of Jupiter. The average meant error as
determined from pairs of observations made oil
same clay is less than 0.25A or 2 percent of the
equivalent width. Using this estimate of the error
the observed differences lit strength of the
methane band at the center of the disk are cer-
tainly real (formal confidence level greater than
0.97). However, there are not nearly enough data to
determine whether the variation is simply secular
or is a function of LCM and surface activit y on the
planet or both.
Observations were obtained Lit several different
points on the disk on the nights of April 27 and 29.
Figure 3 depicts the positior of the aperture with
relation to the major dark bands oil disk of
Jupiter. Also included are the ratios of the equiva-
lent widths with respect to the value at the center
of the disk. The photograph from which the sketch
of the surface features was made was taken on
April 28 at 0401 U.T. at New Mexico State Univer-
sity. There is a definite trend for the band strength
to increase with increasing distance from the center
of the disk. Figure 4 is a plot of the band strength
as a function of the radial distance from the center
of the disk. The solid line gives the secant of the
angle from the sub-earth point. This plot does not
take into account any possible variations due to the
differential rotation of Jupiter. Nevertheless, the
increase with radial distance is very marked. The
values marked "dark band" refer to observations in
which a portion of the aperture covered a dark
belt. Oil 	 basis of only two observations the evi-
dence points to a weakening of the methauie hand
in the dark baits. Further observations will he
needed to substantlate this.
lit this work with that of Mess (1413.3)
who found amarginally significant decrease in
band strength with radial distance it should be
noted that the total observed variation recorded
here is contained within Hess' quoted mean error.
CONCLUSION
This studv has shown that the 60 hand of
n►
 thane at 8190A oil undergoes variations
which Lire statistically significant. It can be stated
tentatively that the band strength increases toward
the limb of the planet and also shows variations
either with time or position on the planet or both.
Finally , the methane band appears .,'ightiy weaker
over the (lark Melts than over the bright areas.
ACKNOWLEDGMENTS
It is a pleasure to acknowledge the able assist-
ance of Norman C. Crowfoot, who wrote the com-
puter programs and assisted lit reductions of
the observations. The question of the methane band
variability was originally called to my attention by
Stuart E
'
Jones of the Lowell Observatory Plane-
tary Research Center staff. Computer time and
some of the observational equipment used in this
study were furnished by NASA Grant NsG-451.
Thanks are also due to Bradford Smith of New
Mexico State University for so quickly providing
the necessary photographs of Jupiter.
REFERENCES
Elvey, C. T. and Fairley, A. S. 1932, Ap. J., 75, 373.
Mess, S. L. 195.3, AZT. J., 118, 151.
Urey, 11. C. 1959, Handbuch d. Physik, 52, 363.
97


Preliminary Observations of the Jovian 6190A Methane Band

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