From Daniel M TROIANI
@. . . . . Mars Grows in Apparent Size!
Jeffrey D. Beish
The International Mars Patrol, an observing program of the Association
of Lunar and Planetary Observers Mars Section
The Early-February 2001 Martian
Chronicle
During the first week of February Mars will begin to rise at 0640 -
0631UT and will unfortunately decrease in declination to -17.5 degrees, at least
for observers in the northeastern United States. Those living in the southern
hemisphere will be treated with a Mars much higher in their sky. Each morning at
6 a.m. (1100UT), Mars will be situated around 43 degrees in altitude in the
southeastern sky. As the month progresses, Mars will slip further to the
southeast.
"Astronomical Seeing" By: Jeff
Beish,
Assistant Mars Coordinator and member of the Computing Section of the
Association of Lunar and Planetary Observers
(A.L.P.O.).
INTRODUCTION
From the first moments this observer gazed into the night sky with a
telescope it was apparent our atmosphere was anything but crystal
clear.
The Earth's sky is not completely transparent and as stable as we
would like it to be. Experienced observers are well aware that turbulent air
currents can cause telescopic images to blur or move around in the eyepiece
field. We have coined the phrase, "astronomical seeing," to quantify, or put
into perspective, the effect the atmosphere has on image quality. Since the
Earth's atmosphere acts like a fluid, we may think of it as a very thin body of
water. Imagine yourself at the bottom of a clear lake looking up at the Moon!
Bad seeing can render a night's observing schedule useless, especially for us
planet watchers. Even though seeing conditions may improve for brief moments
during periods bad seeing, we should pay attention to weather reports. Just
because a weather forecast calls for clear sky that does not mean the atmosphere
will be good for observing.
None of this should be a surprise to anyone who has peered through a
telescope, even at the Moon. At times, the Moon appears like it swimming in
water or above a smokestack! Our atmosphere makes observing Solar System objects
nearly impossible at times.
The words of a great Mars observer, Gerard de Vaucouleurs from his
book, The Planet Mars, says it all:
"It is no exaggeration to say that if, in summer, we look at the Moon
when it is just rising above the level of a tarred road that has been warmed by
the Sun all day, we shall get a good picture of the conditions under which
observers of Mars generally find themselves."
Words spoken for the heart, and from experience. Words echoed by many
oftoday's Mars observers no doubt. First, a look at the composition of our
atmosphere, the effects the upper atmosphere has on "seeing," and a study of
micrometeorology will help readers understand these effects near to the
ground.
A TURBULENT UPPER
Atmosphere
Streams of warm and cold air mixing and flowing together cause
atmospheric turbulence. Most of the disruptive atmospheric turbulence occurs
very near the Earth's surface up to around 50,000 feet. Above this altitude, the
atmosphere begins to thin out and the airflow, or winds, tends to be in the same
direction with each other -- therefore reducing the effects of turbulent cross
winds or violent updrafts. In other words, the higher the altitude the steadier
the airflow is.
The jet stream is a belt or band of rapidly moving air from 50,000
feet in altitude, or above, crossing the mid-latitudes of the U.S. Actually,
there are two jet streams. One in the far northern U.S. and Canada and the other
moves north or south across the center of our country. The jet stream tends to
change in latitude seasonally and will meander across the country like a river
of turbulent water.
The air at altitudes above or below the jet stream may be calm and
flowing steadily in one direction, but the jet stream does not always flow the
same path as the surrounding airflow. Crosswords or vertical wind in this
circumstance causes a decrease in "seeing."
Also, the southern edge of the jet stream will often contain ice
formations or cirrus clouds that tend to help seeing at times and hinder it at
other times. Irregular, disturbed cirrus clouds are not good. Cirrus clouds, or
"mare's tails" as they are often referred to, are usually uniform streaks
indicating smooth airflow. However, the clear region just north of this band of
cirrus clouds may be very turbulent.
These air streams or "thermal currents" causes apparent starlight to
change directions and intensity. Because the density of air varies with
temperature and the refractive index of air depends on the density of air,
starlight does not traverse through it without interference. Thermal currents in
the air have a similar effect as if there were thousands of lenses floating
around in it.
Atmospheric thermal currents also vary the amount of starlight
passing through it and we call this atmospheric "extinction." Random intensity
fluctuations of starlight passing through the atmosphere are called
"scintillation."
You can easily see the effects of scintillation by looking up at
night right after a cold front and see the star twinkle and change colors.
Refraction within the thermal cells also causes the color of the object to
rapidly change.
ATMOSPHERIC PARTICLES CAUSES
TURBULENCE
Air pollution also affects seeing. Seeing in large industrial areas
will have several types of particles and dust materials circulating at lower
altitudes. These particles store heat and will cause thermal air
currents.
The largest polluters are not manmade
though; volcanoes are known to wreck havoc on astronomical seeing. Starting with
the irruption of Mt. St. Helens (northwestern U.S.A.) in the early 1980's, El
Chichon (Mexico) sometime later, and the recent Penetubo (Philippines) irruption
in 1991, we see how these natural phenomena can restrict our sky watching in the
equatorial regions of Earth. That deep red sky at twilight may be beautiful;
however, this indicates that the upper atmosphere is full of particles that
disrupts the air flows and effects seeing. These dust particles fall to Earth in
short order; however, several active chemical compounds remain in the upper
atmosphere for months, even years, to reduce transparency and
seeing.
Dust storms in the African deserts can also cause seeing problems in
some
parts of the southeastern United States.
When this occurs a dusty haze covers the entire sky for weeks and seeing goes
right down the tube, so to speak. All of the above conditions cause starlight to
oscillate about the sky, or "twinkle," and blur, thereby causing them to appear
larger than they really are. In smaller telescopes these fluctuations appears to
shift star images around or make the entire planetary images to oscillate. In
larger instruments, the image tends to blur or smear.
In the case of the small instruments the apparent size of these
"seeing cells," or "thermal currents," are closer to the same size as the
apparent angle of the object we see at the telescopes focal plane. However, in
larger instruments the angular image size is larger so these same "seeing cells"
and disrupt different areas within the image. So the planet image may expand and
contract or blur.
There is some dispute in the scientific community as to what
constitutes a major contributor to air pollution. Some declare the Earth is in
eminent peril due to Man's machinery and others say this not so. To those who
discount the extent to what volcanic eruptions or African dust storms can or
can't do to our atmosphere should go out and look up sometimes. Maybe look up
with a telescope!
MICROMETEOROLOGY
Micrometeorology is the study of the atmosphere from the surface up
to a few yards. Since we cannot do much about the atmosphere, we do have some
control over where we locate our observing site. The Earth's atmosphere is
composed of gases, mostly nitrogen, oxygen -- and water vapor -- and it is not
invisible.
Gaseous vapors have mass and at times may feel like a fluid,
especially in South Florida were the humidity reaches nearly 100% at times.
Humidity is a measure of how much moisture is in the air and indicates at what
point the air will become foggy or hazy. Meteorologists call this point or
condition the "dew point."
Nearer to the Earth's surface there are obstructions, such as
mountains, hills, lakes, trees, buildings, etc., that disrupts the air flow and
is a major cause of bad seeing. Yes, even trees can effect seeing and some more
than others. We will discuss this later.
When planning an observing site it is important to select high ground
if possible. Airflow is less turbulent over hills than in valleys. In addition,
observing from the lee side of a lake can be interesting (the lee side is where
wind blows over the water to you). You will see improved seeing when you move to
the opposite side of the lake where the wind is from the dry
land.
Air circulation over the ocean and shorelines in coastal areas is
very complex and defies a simple or brief explanation here. However, well known
to those living near coastal areas is that astronomical seeing can be excellent,
at times providing the best conditions for telescopic viewing. Conditions near
the coast changes dramatically with the seasons too. This is another very
complex subject and will be omitted as well.
The same thing occurs near buildings that happen to be near lakes or
mountains. The wind may not blow your telescope around as much behind the house,
but seeing will suffer. The peaked roof and heat rising from the house causes
turbulent down drafts that spoils the air flow over your telescope. Move your
telescope to the other side, away from the "lee" side and seeing improves. Trees
will radiate heat and emit vapors at nightfall, therefore spoiling the air
immediately above them. Pine trees are among the worst offenders and this writer
avoids setting up a telescope in a densely populated pine
forest.
The problem in forests is not quite, as simple as previously stated.
The main force that disrupts the air above the forest comes from vertical air
circulation within the trees. Also, in pine forests the thick layer of the heat
storing bio moss (dead pine needles) releases heat plumes after the Sun sets.
Combined with the up and down airflow this heat causes much turbulence over the
trees. However, not all is lost for tree dwellers. A forest may be beneficial to
daytime telescopic observing. It is well know among glider pilots that air above
a forest is calm during day time, giving rise to the suggestion that seeing may
be good during the daylight hours over these trees.
THE SEEING
SCALES
Over the years visual observers have
derived many schemes to describe "astronomical seeing" in a quantitative manner.
First, the scales used by many in the Association of Lunar and Planetary
Observers (A.L.P.O.).
An A.L.P.O. Scale: The first step is to determine the observer's
"personal constant" by using several double stars on a "night of exceptional
seeing", and with the aperture stopped down to 1 inch. This "personal constant,
r, is the separation in seconds of arc of the closest pair which can barely be
separated.
Step two: This requires that, on a night of actual observing, the
observer find the closest double star, which can be resolved, using the full
aperture and then multiply that separation by the aperture in inches, yielding a
value r'. This is used along with r (as found above) to calculate the telescope
efficiency, e, as:
e
= r / r'
and the effective aperture, D', can be
determined from:
D' = (rD) / r'
where D is the telescope aperture in
inches.
Modification of Step One above: the
observer would perhaps be better served by using the methodology described by
Couteau in Chapter 4 of Observing Visual Double Stars where he explains in
detail how to use artificial lighting and small ball bearings to create
artificial double stars located some distance away from the observer. In his own
words (p. 89):
"You will have a stable stellar image,
unaffected by seeing, that can easily be examined comfortably, without twisting
your neck. Reflections from two lamps, side by side, will give a beautiful
double star. The separation can be varied at will, up to the limit of
resolution, and even differences in brightness can be created by moving one lamp
with respect to the other."
By using the formula Couteau provides,
all variables (ball bearing radius, distance between the lamps, distance from
lamps to ball bearing, and distance from telescope objective to ball bearing)
are used to define the separation of the artificial pair in arc seconds. In his
example, he uses a 4mm ball bearing, lamps separated by 10cm and located 1m from
the bearing,
and an observer 100m away, to yield a 0.2
arc second separation.
A suitable "test stand" could be built to allow the "personal
constant" to be determined without regard to whether or not it was a "night of
exceptional seeing." Such a test stand could also be used to compare telescopes
of the same aperture to determine which had the better absolute
resolution.
In Texeraux's How to make a Telescope, Willman-Bell, 2nd ed,
p309-310) and Jean Dragesco's High Resolution Astrophotography, CUP, p3-4) and
noted the following quantitative scale to estimate seeing based on the work of
Danjon and Couder (1935). It also gets a mention in Sidgwick's Amateur
Astronomer's Handbook, 2nd ed, p454-455). This scale provides an absolute notion
of seeing expressed in arc seconds and is not tied to any specific aperture,
unlike some of the other scales in common use e.g. Antoniadi. We may assume the
Rayleigh limit (140/Dmm) as the baseline measure. In use one simply compares the
degree of turbulence in the Airy pattern with the description, and then reads
off the value.
a (in arcsecs) = 140/D(mm)
Table 1. Scale of "Astronomical
Seeing "Scale t-value Description
I
t > 1.5a
Image tending towards a
planetary appearance
II
t = a
Strong turbulence; rings weak or absent
III
t = 0.5a
Medium turbulence, diffraction rings broken, central spot having
undulating edges
IV
t = 0.25a
Complete rings crossed by moving ripples
V
t =< 0.25a
Perfect images without visible distortion and little
agitated
Yet another scale: Harvard Observatory's William H. Pickering
(1858-1938). Pickering used a 5-inch refractor. His comments about diffraction
disks and rings will have to be modified for larger or smaller instruments, but
they're a starting point:
1. Star image is usually about twice the
diameter of the third diffraction ring if the ring could be seen; star image 13"
in diameter.
2. Image occasionally twice the diameter
of the third ring (13").
3. Image about the same diameter as the
third ring (6.7"), and brighter at the center.
4. The central Airy diffraction disk
often visible; arcs of diffraction rings sometimes seen on brighter
stars.
5. Airy disk always visible; arcs
frequently seen on brighter stars.
6. Airy disk always visible; short arcs
constantly seen.
7. Disk sometimes sharply defined;
diffraction rings seen as long arcs or complete
circles.
8. Disk always sharply defined; rings
seen as long arcs or complete circles, but always in
motion.
9. The inner diffraction ring is
stationary. Outer rings momentarily stationary.
10. The complete diffraction pattern is
stationary.
On this scale 1 to 3 is considered very
bad, 4 to 5 poor, 6 to 7 good, and 8 to 10 excellent.
FURTHER READING
Elements of Meteorology, By: Miller and
Thompson, Charles E. Merrill Publishing Company, Columbus, OH. ISBN
0-675-09554-9.
Descriptive Micrometeorology, by R.E.
Munn, Advanced in Geophysics, supplement 1, 1966.
LCCCN 65-26406, Academic Press, 111 Fifth
Ave., New York 10003.
Amateur Astronomer's Handbook, by: J.B.
Sidgwick, Dover Publications, Inc.,
New York ISBN
0-486-24034-7,
1971.
Manual for Advanced Celestial Photography
by: Brad D. Wallis and Robert W. Provin, "Chapter 12, High Resolution
Photography: Seeing," Cambridge University Press, New York, ISBN 0 521 255553 8, pp 257-266.
1988
The Saturn Handbook, Julius Benton,
Association of Lunar and Planetary Observers
(A.L.P.O.).
Observing the Moon, Planets, and Comets,
Clark Chapman and Dale Cruishank, Association of Lunar and Planetary Observers
(A.L.P.O.).
Introduction to Observing and
Photographing the Solar System, Dobbins, Parker, and Capen,
Willman-Bell.
USE FILTERS!
(27 February 2001
email)
@. . . . . See newsletters
at:http://groups.yahoo.com/group/Mars-ALPO/files/Martian%20Chronicles/MC2001-12.htm
Clouds on Mars
Jeffrey D. Beish
The International Mars Patrol, an observing program of the
Association of Lunar and Planetary Observers Mars Section
The Mid-March 2001 Martian
Chronicle
During the last two weeks of March Mars
will begin to rise at 0525 - 0458UT and will unfortunately decrease in
declination from -22.0 to -22.8 degrees for observers in the northeastern United
States. The Sun will rise at 1131UT to 1116UT. Those living in the southern
hemisphere will be treated with a Mars much higher in their sky. Each morning at
6 a.m. (1100UT), Mars will be a little higher in the sky situated at 40 degrees
in altitude in the southeastern sky. Mars will creep higher to 38 degrees by the
end of the month.
Mars increases apparent diameter from
9.1" to 10.3" during this period.
2001 Mar 18, Ls =
132.3ｰ, De = 2.8ｰ, Ds = 18.1ｰ, Dec = -22.0ｰ
In 1954, a remarkable W-cloud formation was found to be recurring
each late-spring afternoon in the Tharsis-Amazonis region 1954 was an Aphelic
apparition). A decade later, Charles F. ("Chick") Capen proposed that the
W-clouds are orographic (mountain-generated), caused by wind passing over high
peeks. Indeed, in 1971 the Mariner 9 spacecraft probe showed them to be water
clouds near the large volcanoes Olympus Mons (longitude 133・#8249; west,
latitude 18 north), Ascraeus Mons (104ｰW,
11ｰN), Pavonis Mons (112ｰW,
0ｰN), and Arsia Mons (120ｰW,
9ｰS) [See Figure 1]
Figure 1. Images of Mars showing W-clouds over Tharsis volcanoes in 1999.
David Moore, C (center Right) by Maurisio
Di Sciullo, and D (right) Antonia J. Cidadao.
The W-clouds should be active during the 2001 apparition beginning in
late February or early March (125ｰLs) through June (176ｰLs) and, perhaps, later in the apparition, during early northern autumn
(200ｰLs). Although often observed without filters, they are best seen in
blue or violet light when they are high in altitude and in yellow or green light
at very low altitudes.
Figure 2. Images of Mars showing W-clouds on morning limb over
Tharsis.
Image by Maurisio Di Sciullo.
Observers often see these orographic clouds in an unusual pattern
resembling dots on Domino chips and have coined the phrase "Domino effect" that
may appear around 120ｰ - 125ｰLs. This may be the early formation of the W-clouds; at least before
each orographic cloud is connected together by blue-white clouds bands formed by
winds or temperature gradients [See Figure 3]
Figure 3. Image of Mars showing orographic clouds over Tharsis volcanoes in 1999 before they connected to form the W-clouds. Formation suggests a "Domino effect" by observers.
Figure 4. Mars Global Surveyor Mars Orbiter Camera Image of W-Clouds
forming over the Tharsis region of Mars. The huge volcano Olympus Mons and
orographic cloud is located in the above image to the upper left. Slanted across
the left of center are three orographic clouds over the volcanoes; 1) upper
center is Ascraeus Mons (104ｰW, 11ｰN), 2) to the left and down is Pavonis Mons (112ｰW,
0ｰN), and further down and left is Arsia Mons (120ｰW,
9ｰS). Low level clouds are present over Solis Lacus and Thaumasia
(center). Clouds can also be seen in Chryse (center) and north to the 3west of
Lunae Lacus.
DISCUSSION
The International Mars Patrol (I.M.P.) has initiated an observing
program for intensive investigation into these phenomena and will appeal to all
planetary observers using CCD technology to assist us in this important study.
New technologies, such as CCD cameras, sophisticated computer hardware and
software, and large-aperture planetary telescopes have given rise to a virtual
explosion in advanced techniques of studying our Solar System. Never before have
we been able to readily detect the delicate wispy Martian Topographic and
Orographic Clouds so well as we do now with CCD
imaging.
The Hubble Space Telescope (HST) and the Mars Global Surveyor Mars
Orbiter Camera have revealed that these clouds follow a similar trend line or
forecast predicted in recent A.L.P.O. meteorological studies of Mars.Topographic
and Orographic Clouds are best detected visually through a light blue (W38A or
80A) and deep blue (W47 and W47B) Wratten filters and may be photographed or
imaged in blue or ultraviolet light. They are sometimes observed quite easily in
integrated light (non-filters) as well.While it is not the purpose to discuss
the physics of these clouds we never the less draw certain conclusions from
observational evidence. Questions remain that may be answered with high-tech
observing techniques by amateur astronomers. There is no reason we cannot at
least serve as long termed clouds reporters between scant times of HST observing
periods.
Clear and Steady Sky for
Yawl!
(10 March 2001 email)
Jeffrey D. Beish
The International Mars Patrol, an
observing program of the Association of Lunar and Planetary Observers Mars
Section
A Martian Chronicle
Extra
During February 2001 observers sent the
Mars Section several CCD images that contained a brighter than "normal" spot in
Chryse (32ｰW, 08ｰN). Mars was very small in apparent size during February and the
resolution of the images prevents positively identifying the bright spot as
dust. In Figure 1 several images illustrate the difficulty in determining the
nature of bright areas on Mars, especially when Mars subtends a small angle as
it did in February. Thanks to CCD technology we don't have to reply solely on
visual reports or images taken with film. It would be virtually impossible to
photograph Mars at 5 or 6 seconds of arc in apparent
diameter.
Figure 1. Images of Mars taken by observer using a variety
of CCD cameras. The left-hand image by D. Parker in red light shows Chryse to be
brighter than the adjacent desert regions to the east (area at equator in center
of image to right or morning limb). The next image is a composite of several
hundred video images taken by George Hall (integrated light). Bright area is
obvious in same area as indicated in Parker's image. Mellows center image also
shows Chryse brighter than other desert regions. The three images to the right
by T. Ikemura also show a brighter than normal Chryse.
Chryse is bright as a general rule and the unsuspecting observer may
think they see dust clouds in the area. At times we see areas in Chryse that may
be bright in all colors indicating a "white area" or low fogs, frost and hazes.
Normally blue, blue-white or white clouds are bright in blue light only;
however, if a cloud contains a sufficient amount of dust then it will brighten
in red, even in green light. The ALPO Mars Section researchers have written
volumes of material on these clouds, or whatever they are, and have not drawn
any substantial conclusions as of yet. However, when we do see bright spots in
Chryse they will often turn out to be dust clouds.
Classically, the storms occurring during southern summer are larger
and more dramatic: they can even grow rapidly to enshroud the whole planet.
Please remember that these global dust storms are quite rare. Only five have
been reported since 1873, and these have all occurred since 1956. Much more
common is the "localized" dust event, often starting in desert
regions
near Serpentis-Noachis, Solis Lacus,
Chryse, or Hellas. During the 1997 apparition, CCD and HST observations revealed
localized dust clouds over the north polar cap early in northern
spring.
During the 1960's and 1970's heyday of space missions to Mars we
learned that amateur observations were of vital importance to the safety of
landing machines on that planet. In a J.A.L.P.O. paper titled, "A Season for
Viking," Chick Capen accredited A.L.P.O. observers with alerting space agency
officials to the highly active region of Chryse. He wrote that the Chryse region
exhibited "a history of seasonally controlled weather." Chryse was a target for
the Viking I Lander and they had contracted several planetary astronomers to
detail the region as a possible landing site. Capen was one of those chosen and
he reported information A.L.P.O. observers had sent him along with his own
telescopic observations at Lowell Observatory.
Indeed Chryse is an active region. He writes, "During the Martian
northern summer and winter, when one or the other of the polar caps has about
completed its thawing phase, there have been observed morning bright patches
which were interpreted to be ice-fogs or ground frosts formed during the chill
of the night." [Capen, 1976]. This interpretation is still to be fully verified
and he was optimistic that ground-based amateur observers would contribute to
solving this weather phenomena on Mars.
From my own observations Chryse has been a more active than past
observers had believed. Several dust storms have been observed in this area and
to rage on for weeks. Dust clouds have been observed to cross from Chryse south
into the darker regions and flow into and out of Eos - Aurorae Sinus and
continue on into the Solis Lacus area. Although Chryse is reported bright in all
colors during most seasons observers should be especially aware of the area
during the end of the polar cap thawing period. This story of weather in Chryse
may not be the whole however.
During May of 1982 this author tracked bright dust clouds on the
morning limb west of Solis Lacus extending northeast toward Tithonius Lacus and
Lunae Lacus. Dust clouds and haze north of Solis Lacus extending onto morning
limb and into Margritifier Sinus, adjacent to Chryse. These features are close
by to Chryse and dust was seen to cover the Ganges almost completely. Chryse
remained bright with dusty haze for weeks afterward.
Several adjacent Martian areas to Chryse
also exhibit active weatherpatterns. One in particular is Ophir, a bright desert
region sandwiched between Aurorae Sinus and the dark blotches and canal like
features connecting to Coprates. The Ganges (canels) borders Ophir to the east
and when the Coprates is dark Ophir will appear very bright giving observers
cause to claim that a dust cloud may be present there. While A.L.P.O. observers
have in fact reported dust activity in Ophir it is usually in conjunction with a
confirmed dust storm in Chryse or Solis Lacus. Detecting the positions of dust
clouds is difficult even when visual observing Mars with filters. So we then
alert astronomers equipped to image the planet at a moments
notice.
REFERENCE: Capen, C.F., "A Season for Viking," JALPO, Vol. 26, Nos. 3-4, August 1976, Page 41 - 46.
(18 March 2001 email)
Daniel M TROIANI (IL, USA)
Mars
Section Head Coordinator, ALPO
dantroiani@earthlink.net
dtroiani@triton.cc.il.us
http://www.lpl.arizona.edu/alpo