M45, The Pleiades (Tomahide Nakaegawa) http://www.ne.jp/asahi/nakaegaw/piz/)
Season: Currently autumn in the Northern Hemisphere (although "winter" began for most people over 55○ N on Sep 21.)
(Biography: Steve Yaskell is a science author in astronomy and natural history. His articles and insights have appeared in many publications around the world, such as Great Britains' Astronomy Now, as well as Sky & Telescope and The Sciences in the USA, among others. He recently co-authored a book on solar astrophysics and severe global climate change at the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts, USA. [The Maunder Minimum and the Variable Sun-Earth Connection, WSP:2004])
NAR obtains permission to use material by solicitation. If NAR cannot obtain it at web addresses, NAR publishes with the proviso that NAR will remove it instantly if the discovering author(s)so wishes. All reasonable efforts to contact content contributors are made by NAR. If you wish to reprint articles in whole or part, please obtain permission from NAR. Or drop NAR an email at starthrower1@msn.com. Clearance for rewriting and editing timely news material from Science Magazine was granted by Elisabeth Sandler at the American Association for the Advancement of Science(esandler@aaas.org). This rule generally holds for most scientific journals.
________________________________________________________________
Regular quarterly features
*The quadrant
*Star hopping with
small telescopes (in Orion and environs with Steven H. Yaskell)
*Star hopping with
large telescopes (in Auriga and Gemini with Darrell Abrahams)
*Coordinates over
50○ N (Sun, Moon, Moon phases and the planets)
*NAR guest feature
(Boris Gudiksen reports on his research, performing simulations of the solar
corona)
*Astronomical
science news (Nitrogen very common in space:Hawking backtracks?)
*In
astronomical history (micrometers: three 17th Century views)
*Equipment
review (with Ed Ting) (welcome to the Intelliscope)
The quadrant
\\\ The way it
is______________________________________
Living in the north takes
on its own powerful persona for the star observer. Yeah, sure: you can say that
about any place you choose to live. But only the northern clime inhabitant has
that special view. Call it perserverance. Call it doughty resilience. Call it a
successful battle against the effects of cold, dark, cloudiness, storminess and,
alternately, brightness and blandness. Stamina helps too, of course.
You live for those few good
nights and savor them like a good wine. The rest of the time is spent inside,
usually thinking about what you're going to do on the next available clear and
scintillating night. The southern astronomer is spoiled with fine weather. The
northern astronomer is always prepared in advance. They have no choice.
In these issues of the
Northern Astronomical Review we choose to take on some of the more positive
aspects of this living persona and give it a body. Content here will be aimed at
those who can't fit the bill at the median "40○ " and who find themselves
imagining the usual star chart geared for this always a little lower in some
areas, higher in others. Seeing takes on its own special flavor up here, too.
Doesn't it? Some of us have very little light pollution to worry about : that's
for certain. At other times of the year, you'd best be either an avid radio
astronomer or a solar observer. Many of us don't see the stars for upwards of
three months or more in these environs.
Why do we do it? Heck,
that's easy. Some of us get married and find ourselves getting by here better
than we would further south. We take north our love of astronomy and adapt it.
Others are born in these parts and, as star students, become entranced with that
sky spreading from late July through early April, then wonder what the rest of
it looks like (they find out on trips to Hawaii). Still others are stuck in some
country's armed services, trying to make the best of their star charts and
books, and lives. All calculated for 40○ .
(...Hey, where's
Sagittarius?)
The NAR is also about
science, and not consensus/debate science, either. When we do have it, we'll
have science as the scientist who publishes here wants to describe it. Not as
the editor thinks an imagined readership wants it. All my career as a science
and technical writer and editor (and as a scientist) has been dedicated to this
end, for one. We do not intend (to modify an ancient expression) to ignore "the
body shop exterior" of science, either. Look for a good deal of beauty in these
pages. If it's possible, we'll try to get it in here.
Steve Yaskell
Star hopping with
small telescopes
A hunter of some
starry sisters
Steven H. Yaskell
With dark skies, we begin
in mid autumn to take a sidereal turn allowing us to face out of our own solar
system, and into the wide universe at large. It is appropriate that as we go
back to work or school to face the deeper and more mysterious, we leave the
familiar backyard of our own home – very much as we abandon the grill parties
and picnics. The planets and Sun are put away. Now is the time to start looking
at cosmic gas.
An early arrival at our
latitude now is the Pleiades, or Seven Sisters (M 45). It has been up for some
time by November, and takes a perfect viewing position in Stockholm’s
(alternately, Fairbanks, Alaska's) night skies for the rest of the autumn and
into winter. So large it actually makes a fuzzy silver background object like a
cart, it is best seen (I feel) with binoculars.
An enormous open cluster
found at about 3h 45m Right Ascension, many stars being 3rd magnitude, the
cluster is young (about 20 million years). Indeed, the young stars radiate
nebulous reflections and seem to join in a star haze within the official range
of the constellation Taurus.
A most beautiful line in
English poetry is connected with M 45. Alfred, Lord Tennyson saw the Pleiades
“glitter like a swarm of fireflies tangled in a silver braid:” And so do we
(don't let Tomahide Nakaegawa's blue background fool you: that is a consequence
of photographic development.). They were supposedly the seven daughters of
Atlas. To the Chinese, according to Richard Hinckley Allen, they were sisters,
all right. Not of royalty, but of industry. (Ten degrees southeast of the
Pleiades, Taurus has another group of “half sisters” known as the Hyades.) Some
later myths describe them as chickens, and several ancient poets knew the Seven
Sisters as rock doves flying away from the hunter, Orion, according to Allen.
Orion’s first large star to
poke Stockholm’s (and probably Fairbanks') sky is Betelgeuse (A Orionis) a
reddish 3rd magnitude variable. Orion’s body is found in the lower, deep
southeastern horizon early on October mornings, gradually lifting into an arc
that will skirt the sky until late April. At that time, it sinks into the west
with just as much wide reaching finesse as it rose six months before. Equally as
unmistakable on these cool nights, find the diffuse nebula complex called
M42-M43 opposite Orion’s 3-starred “belt” at c. 5 h 35 m Right Ascension.
These nebulae, when seen in
a small telescope (2.4 inch to 6 inch) are revealed for the star-birthing
regions they form. In a scope the center portion takes a furry fish hook shape,
punctuated by the ominous “trapezium,” a glowing area of heated, ionized gas
with several tiny infrared infant stars. The layers of the trapezium consist of
an Oxygen III (OIII), a Hydrogen alpha (Ha) and an expanding ionized cloud. The
gas cloud around the trapezium will one day disperse to perhaps form into a
Hydrogen II region.
Whatever objects you search
for as autumn gives way to the long winter we are used to, don’t forget to the
left of Orion is Monoceros, the Unicorn. Monoceros consists mostly of faint
stars, yet objects like the Rosette Nebula can be seen even through Stockholm’s
(and Fairbanks')light pollution.
(About the photos:
Tomohide Nakaegawa is an amateur astrophotographer from Japan. View his
homepage, “Piz’s Jewel Box.” He has photographed most commonly seen catalogue
objects in a way many small telescope and binocular users see them. )
Star hopping with
large telescopes
Autumn sidekicks
Darrell Abrahams
As a boy I was always
fascinated by Tonto, while the Lone Ranger was a bit of a stiff. Inspector
Clouseau would start to get dull but then Kato would appear. Where would be the
Men in Black without Will Smith? The same goes for some deep sky objects. Sure,
that showpiece looks good; but did you ever notice that little object right next
to it? Here are a few “sidekicks” that I always enjoy checking out while in the
showpiece area.
M 33 in Triangulum. Great
face on spiral galaxy in our Local Group. Easy to find: Just drift from M 31,
the Andromeda galaxy, down through Mirach (beta And) and that same distance and
direction, to M 33. Large: 40' by 60' but quite diffuse. So wait for it. Let
your eye soak up the spiral structure, and then, near the north edge of the
galaxy, look for the HII emission cloud NGC 604. At first it appears as a pair
of stars, only one is fuzzy. With more magnification it is definitely a nebula.
This is a good test for a four inch scope and is a good indicator of sky
conditions. There's a fantastic Hubble shot of this thing which shows it is
another Orion Nebula, only NGC 604 is actually ten times bigger and in a galaxy
far, far away.
M 38 in Auriga. One of
those three great Messier clusters in Auriga. Actually the more northerly one
with the spidery arms. Uranometria Deep Sky Field Guide says: rich in stars,
(160); moderate brightness range; slight central concentration; detached. But
just 30' south of M 38 is the open cluster NGC 1907, a beautiful sidekick. At
one third the size (5') moderately rich in stars (113); small brightness range;
strong central concentration; detached. But with the brightest star at magnitude
11.0 one must magnify to enjoy. Enjoy.
M 35 in Gemini. Another
great Messier open cluster. Easy hop off Castor's foot (a lot like finding M 11)
seen in 7 X 50 finder. Rich in stars; large brightness range; no central
concentration; detached; very large (25') brightest star magnitude 8.0; 434
stars (i.e.: in photos). But hiding 10' off the edge of it is the open cluster
NGC 2158 (see yellow circle in photograph). To find this, hop from the brightest
star in the field (5 Gem) and slide across the top (bottom, side) of the big
cluster the same distance past. If it isn't there, then slide across the other
side. You're looking for a small glow with a star or two. A field guide says:
rich in stars; large brightness range; slight central concentration; detached;
overall cluster magnitude 8.6; brightest star mag 15.0; 973 stars. Wow. This
cluster is 6 times farther away than M 35 and is one of the most remote open
clusters that can be seen in small telescopes. The Night Sky Observer's Guide
says that if this cluster was as close to us as M 35, it would be one of the
finest open clusters in the sky. I always thought this to be a test for a four
inch scope until I saw it in a four inch Takahashi refractor and it hit your eye
like: “Nice big open cluster…but what is that?!” My 16.5 inch gives a bright
glow with 12 to 16 stars.
Remember, Captain James T
Kirk was good, but Mr. Spock was great.
(About the author:
Darrell Abrahams is a member of the Fraser Valley Astronomers Society of British
Columbia, Canada, and is an avid deep sky observer.)
Coordinates over 50○
N
Sun, Moon and
planets
Courtesy U.S. Naval
Observatory and Stardate Online
MICA is the Multiyear
Interactive Computer Almanac. With it you can obtain sidereal time to your
specific location for the Sun, Moon and planets. To use MICA Version 1.5
(available as test or download) you will need to know your latitude and
longitude. To find Greenwich Mean Time (which is also Universal Time[UT]) find
your local time zone and count forward - or backward -to the time as it would be
at Greenwich (in the UK). MICA uses Universal Time (UT) for all its
calculations. All you need do is add UT and your latitude and longitude and
press a button to get rising and setting times of various Solar System objects.
(See link below)
To calculate for planetary
and solar postions, see link below NAR guest feature
Simulations of solar
coronal heating: an answer to this question at last?
Boris V. Gudiksen
The Sun is the nearest
star, and the only star where we can resolve details on the surface. Only in the
last 100 years have we been able to answer most questions about the Sun. One of
the only major problems remaining involves the question of solar coronal
heating.
________________________________________________________________
________________________________________________________________
M45, The Pleiades (Tomahide Nakaegawa).
________________________________________________________________
________________________________________________________________
To find
Moon phases for the month
http://www.stardate.org/nightsky/moon)
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Figure 1. The solar corona seen in the extreme ultraviolet part of the spectrum, showing large loops of hot plasma caught in the Sun’ s magnetic field(Transition Region And Coronal Explorer [TRACE] Lockheed Martin).
The solar corona is the
outermost layer of the Sun. It can be seen during a solar eclipse as a ``crown''
(coronae means “crown” in Latin) surrounding the dark moon shadow. The solar
surface is called the photosphere. But since there is no solid surface on the
Sun, it is defined as the layer where visible light is emitted that reaches us
on Earth. Below the photosphere the Sun can be modeled with great precision.
In the inner two thirds of
the Sun, the energy produced in the solar center is transported outwards by
photons. Since the gas is very dense, a photon only travels a short distance
before being reabsorbed. This happens so many times that in spite of the large
velocity of light, it takes a photon about 100,000 years to reach the surface.
About two thirds of the way out through the Sun, the heat generated by fusion in
the Sun’s core can no longer be transported efficiently by photons. Therefore,
hot gas flows up to the surface where it is cooled and then sinks back down to
be reheated. This part of the Sun is called the convection zone. The effect of
the convection can be seen on the surface of the Sun as bright blobs of
ascending gas surrounded by dark lanes of descending gas (see Figure 1). Since
the Sun’s energy is produced in the solar center, intuition leads us to believe
that the temperature should decrease with distance from the solar center. This
is true from the solar center with a temperature of more than 10 million Kelvin
(K) to the 5500 K photosphere. But then something unexplained happens. Over a
distance of only 0.2 % of the solar radius the temperature skyrockets back up to
1 million K.
The solar corona’s high
temperature was discovered by the Swedish physicist Edlèn, who in 1939 showed
that some of the observed spectral lines from the corona were of iron, ionized
13 times. Until then the spectral lines had been assumed to be from an element
called Coronium. The high temperature means that the corona emits primarily in
the extreme ultraviolet part of the spectrum. Since the Earth’s atmosphere
absorbs ultraviolet radiation efficiently, the corona cannot be studied well
from Earth. Satellites are launched in order to get good observations of the
corona.
Plasma and the
heating problem
The increase in temperature
demands that energy is injected in the corona. Ever since it was discovered that
the corona was so hot, researchers have been trying to find a mechanism that
could provide this energy. Absorbed light from the photosphere cannot heat the
gas to a higher temperature than the medium that created the radiation, namely,
the 5500 K photosphere. Heat conduction cannot be the mechanism, since that
would mean heat runs from the “cold'' photosphere to the “hot” corona. Thus a
more complex mechanism must be at work.
The famous Swedish
physicist Alfvén proposed in 1946 that perhaps magneto-acoustic waves deposited
heat in the solar corona. But it turned out that the theory behind this was so
complicated no one gave it any credit. (The theory Alvèn based his work on was
not well developed at the time because it treated gas in a special state which
is not easy to reproduce in a laboratory.) Gas at high pressure or high
temperature behaves somewhat differently than normal gas as we know it in, for
instance, our atmosphere. The reason is that under more extreme conditions,
electrons are no longer bound to atomic nuclei. They flow freely in large
numbers. This makes the gas (or plasma, as it is often called) an extremely
efficient electrical conductor.
Plasma is sometimes called
the "fourth state" of matter, where the first three states are liquids, solid
and gases (think of water, ice, and water vapor). Plasma’s low electrical
resistivity makes it very easy to induce electrical currents, which then
produces magnetic fields. It is the properties of plasma that makes the Earth
and the Sun have a large scale magnetic field by what is called an astrophysical
dynamo process.
In the Earth, the magnetic
field is generated by the fluid iron core, while in the Sun, the magnetic field
is produced in a thin layer just below the convection zone. In the Sun, the
magnetic field that is produced not only shows up as a large scale field as on
Earth, but also as smaller concentrations of magnetic field. The biggest
concentrations of magnetic fields, and which are strong, we know as sunspots
(Figure 2).
Most small scale magnetic
field does not come in the form of sunspots. It is found in much smaller
concentrations scattered across the entire solar surface. The reason why
sunspots are dark is due to another of plasma’s properties. The magnetic field
makes it impossible for the plasma to move perpendicular to the magnetic field,
and that stops the turbulent motion inside sunspots, inhibiting the convection.
The plasma inside the sunspot cools because no new energy comes from deeper in
the Sun, making them seem darker than the rest of the solar surface. Another
effect of the magnetic field is that heat only flows alongside the magnetic
field. The heat conduction along the magnetic field is very efficient, quickly
removing any difference in temperature along the magnetic field. The consequence
of this effect is the loops seen in Figure 1.
These loops were first seen
during the American Skylab missions in the early 1970s. They gave the first
clues as to what could be heating the corona. It was found that whenever there
were sunspots and magnetic activity on the Sun, the corona was hotter than
otherwise. Thus it was now known that whatever mechanisms were heating the
corona, they must have to involve the magnetic field somehow.
Theories behind the
heating
Out of a large number of
theories attempting to explain coronal heating, two competing theories have
survived scrutiny and could provide the answer.
The first is a further
development of Alfvén’s 1946 theory. It is based on “damping” waves (as when
sound travels through a wall, the wave’s sound gets fainter). On Earth we in
principle have only sound waves, which are changes in pressure. In the
magnetized plasma of the Sun there are more kinds of waves. They come in three
families: sound waves, magneto-sonic waves, and pure magnetic waves (now called
Alfvén waves). The idea is that these waves will be produced in the turbulent
photosphere, and move into the corona, where they will be “damped.” Since waves
carry energy, damping them must mean that the energy they carry is lost. Since
energy cannot simply disappear, the energy in a wave turns into heat if it is
damped. This is the idea behind the heating mechanism possibly at work. It turns
out that the change of temperature between the photosphere and the corona acts
almost like a wall for the sound and magneto-sonic waves, which means they never
make it up into the corona. The Alfvén waves do not have this problem. But since
they are so resilient, it is also very difficult to damp them once they reach
the corona.
The second theory was
proposed in the 1970s. The basic idea at work here is that small concentrations
of magnetic field get moved around by the turbulent plasma in the photosphere.
Since the magnetic field looks like loops and comes back down to the
photosphere, it can easily be imagined that moving the “foot points” of the
magnetic field around can braid it into a complex pattern. Many have done an
experiment in school where a magnet is moved inside a coil of wire and have seen
that it produces an electrical current. The same thing happens in the corona
when the magnetic field is moved around. That is, an electric current is
produced. The idea is that the corona’s electrical resistance causes heat to be
produced, just as an electrical transformer for instance gets very hot from the
current running through it. However, not enough heat is produced, since
electrical resistivity happens to be low in the corona.
It turns out that if one
braids the magnetic field too much, it will snap and reconfigure itself a
process called magnetic reconnection. Reconnection of strong magnetic fields
produces solar flares. Flares are large energy outbursts that can heat the
surrounding plasma up to 30 million K. At times, such explosions eject large
clouds of very hot plasma called Coronal Mass Ejections (CMEs). If such a cloud
hits Earth it can destroy satellites, disrupt power grids, and cause northern
lights. It is expected that most reconnections only produce small amounts of
energy. But they are very numerous and the sum of them will be enough to heat
the corona.
It has until now not been
possible to estimate the amount of heat each of the mechanisms would produce in
the corona. Observations of the processes are in general very difficult because
neither the Alfvén waves nor the reconnection of the magnetic field give out
large amounts of energy. We do know that Alfvén waves are present in the corona
because they have been measured directly in the solar wind, so heating by waves
is certainly possible. Small energy bursts in the corona have been observed in
great numbers, but we cannot be certain that they are really reconnections, and
furthermore, theory predicts that most energy coming from reconnections would
happen in very small bursts; smaller than we would be able to observe. In order
to solve this problem we had to produce a much more elaborate model than
previously used. Over the last few years, computers have developed enough to
make it possible to perform a trustworthy simulation of the solar corona.
There are a number of
problems involved in creating such a simulation. In order to complete the
simulation within a reasonable time, one makes approximations. The effects of
these approximations and when they can be used need to be investigated before
they can be used, yet still provide a reliable result. Luckily, some of this
work had already been done some years ago. We could therefore concentrate on the
physics.
We simulated a patch of the
solar surface 60,000 km on a side and 40,000 km up into the corona. (These
distances sound very large. But remember that large sunspots can be several
Earth diameters across, and one Earth diameter is 13,000 km!) We felt that the
velocity pattern of the turbulent photosphere had to be included with great
precision. This had never been done before. We had to invent a way to create the
typical velocities of solar granulation (this is rising hot gas drawing down the
cooler gas that when seen with a telescope resembles granules.) With that and a
magnetic field observed on the Sun, we began the simulation. It ran for about a
month on a supercomputer with 16 processors.
The results were very
encouraging. The braiding of the magnetic field created exactly the right amount
of heat necessary to keep the solar corona at 1 million K. This result made it
obvious that at least a large fraction of the energy needed to heat the corona
comes from the braiding of the magnetic field. Another important feature of the
solar corona is the very thin loops seen in the ultra violet observations of the
solar corona. In a simulation, we can essentially reproduce what the satellites
would ''see'' if they observed a part of the corona like the simulated one. This
can be done because, solving all the equations controlling the plasma, we get
the density and temperature of the plasma, making it possible to calculate how
many photons the plasma produced. By getting information about the technical
details of the satellite, we can reproduce the image the satellite would create
by observing the simulated box (see the simulation result in Figure 3).
Figure 3 shows one such
reproduction. It can only be qualitatively compared to details shown in Figure
1, as the satellite can ''see'' a much larger volume than we can simulate. It is
obvious, however, that this simulation can also reproduce thin loops like the
ones seen in Figure 1.
These two features of the
simulation essentially solve two problems at once. It has for some time been a
mystery what selected a certain loop to be lit up and become observable in
ultraviolet by our satellites. Since there are only a small number of them in
Figure 1, then they have to be special in some way.
For some time, observers
tried to figure out if the loops had something in common that made them
different from the rest of the corona except that they were observable. But
solar astrophysicists have not been able to produce results. That is not
surprising when looking at the simulation. It turns out to be a complicated
process. The history of a loop is divided between the periods, with many
reconnections, and therefore, much heating and periods where not many
reconnections happen. Thus, the plasma in the loop cools down. Heating a loop
will make some of the heat run along the loop into the cool photosphere where it
makes the now heated photospheric plasma expand up into the loop. This will
increase the density in the loop, and the higher density will increase the
number of produced photons, thereby making the loop easier to observe. A clearly
observable loop thus needs a history where a lot of plasma has been moved into
the loop from the photosphere, but at the same time, have the right temperature.
All in all, we have now
come a step closer to solving the last of the major problems the Sun has to
offer – the secret of solar coronal heating.
(About the author: Boris V.
Gudiksen is a research solar astronomer at the astrophysical institute of the
University of Oslo, Norway.)
Astronomical science
news
Molecular
Nitrogen (N) in space Nitrogen 2 (N2) has
been discovered in the interstellar medium (HD 124314 in Centaurus). Searches
for this diatomic molecule have been hampered by a lack of dipolar (rotational)
transitions and so, cannot be detected through millimeter wavelength
observations of rotational emission lines or absorption or emission bands (using
infrared spectroscopes). It is predicted that N2 is the most abundant
Nitrogen-bearing molecule in interstellar space. (Editor’s note: That Nitrogen
(N) makes up over 70% of Earth’s atmosphere should be kept in mind when
considering the importance of this element to life as we know it.) T. P. Snow,
Nature June 2004)
No “quantum
leaps” this time? Information not only is
not destroyed – as matter neither can be – nor will it disappear from our
universe. This is the latest declaration from one of the greatest living
relativists, Stephen Hawking. It is also a stunning reversal of his previous
claims. For thirty years Hawking taught us
that black holes, for one, destroyed information. Additionally, information,
could vanish from our universe and, ominously, appear in some other one. This
had implications for wormholes: time travel, in other words. For another, it
discounted the very claims of fellow relativist Albert Einstein so long ago and
before him, Benedict de Spinoza. For matter, they asserted, could neither be
created nor destroyed. At the heart of this
cosmology debate are the relativists (Hawking) and the quantum theorists. Old
laws would have to be broken, but whose? The relativists thought quantum theory
flawed in some way. The quantum theorists, in turn, believed the something
unexplained or overlooked must salvage information from destruction, suspecting
Hawking of error. At a conference in Dublin last spring Hawking backtracked on
information destruction, citing mathematical difficulties, and conceded that
information cannot be so eliminated. Spinoza
could have told him. (Charles Seife, Science, August 2004)
In astronomical
history...
Micrometers:
"all in a turn of the screw" : (three variations of a Seventeenth Century
invention)
Steven H. Yaskell
In Tycho Brahe’s 1500s, one
without telescopes, it was impossible to see small angular separation between
objects in space without inaccuracy. Small separations had to be measured
without moving from a sighting device, to the objects, and back again. A
micrometer was needed.
Even when the telescope was
first used in astronomy in the early 1600s such an instrument was anticipated,
or maybe invented, by the Englishman William Gascoigne. As with many great
things in science the idea was accidental:
I have either found out, or
stumbled on…a most certain and easy way, whereby the distance between any the
least stars, visible only by a perspective glass, may be readily given, I
suppose to a second…strangely precise.
Like using the telescope
for different reasons, the micrometer was also a strange find. Gascoigne,
writing to Episcopal minister and mathematician William Oughtred in the 1640s,
told of how he was fooling around with lenses one day when
it pleased the All Disposer
(God) at whose direction a spider’s line drawn in an opened case could first
give me (that is, it first gave him) by its perfect apparition, when I was with
two convexes trying experiments about the sun, the unexpected knowledge.
And also like many things
in science, this is where the trail ended, at least where Oughtred was
concerned. Years later, after Gascoigne’s death in the English Civil War (and
after the micrometer was invented and made by the French astronomers Jean Picard
and Adrien Auzout) an Englishman named Robert Towneley contacted the English
Royal Society.
Henry Oldenburg, the
influential Royal Society secretary at the time, was told by Auzout that he and
Picard had been using a micrometer for years in Paris. This probably hastened
Towneley’s letter to Oldenburg. For he had news about an earlier English
invention of the same tool. Towneley claimed that before the Civil War Gascoigne
had already designed and made an instrument as sensitive as the Parisian
astronomers’. The French had been making accurate measurements with such a
device for some time. Yet Towneley claimed he owned the first instrument ever
made by Gascoigne in the 1640s. (Whether it actually existed or not is another
question.)
_____________________________________________________________________
_____________________________________________________________________
The letters by Gascoigne
certainly reveal that the idea of a micrometer was in the English mind by 1640.
That the French independently invented it is by no means far fetched. Picard had
made other instruments.
Gascoigne’s invention
operated as a brass disc moving inside an oblong brass box. A well-made screw
ran along the box’s entire length, fastened at each end. This is so the handle
could be turned without any unsteadiness. A socket fitted into a long bar, onto
which was set a moveable sight, was used to measure angles between celestial
objects against a fixed sighting device. Each division made along the long bar
corresponded to one screw turn, coordinating these sighting devices.
Hooke’s drawing is a
three-dimensional wonder of technical description (Hooke had practically no
equal here, then.) But the cruder, workbench-style drawing of Auzout and Picard
shows a more functional, non-three dimensional view of a tool they had been
using since at least 1666.
A unit marked LMNO in the
diagram contained another lettered RSTV, this latter section movable within
LMNO. A screw (PQ) moved the units, the screw attached to a pointer moving
across a circle (W) graduated to show sixtieths of one full screw turn. A pair
of hairs on the two frames was used to measure the image, the separation
measured in whole turns and a fraction of a turn. Upon instrument calibration,
the rough measurements were converted into angular separation. Another frame
marked TVON within RSTV contained other hairs. As with more modern micrometers
(the filar) the angular measure was made by separating the hairs through a
series of turns, laid perpendicular to the equator, then noting on a pendulum
clock the time taken by a star (whose declination was known) to cross from one
hair to another.
The Danish astronomer Ole
Römer developed the best micrometer known to authorities at the time. Without
any prior knowledge of the one made by Picard and Auzout (so he claimed) Römer
invented it while in Paris. Three quadrilateral frames (B,C, and D) D and C
contained the cross hairs. B had a pair of horizontal bars which had three
grooves. There were three fixed cross pieces, and a sliding stop moved by a
screw (H). An M-shaped spring (in B) moved a movable stop (F) against the end of
the screw, making it move steady. It was constructed to minimize screw wear,
such wear usually accounting for many observational inaccuracies. Apparently,
this lack of wear was the chief advantage of Römer’s device.
The device was attached to
a telescope’s focal plane. The screw was turned until the distance between a
movable thread and a fixed one coincided with the diameter of the object viewed.
This is not the entire
description of how these micrometers worked. Nor are these the only micrometers
that were made in this period (there was one by Christiaan Huygens, for
instance). But among the history of these three, a non-European observer (me)
sees a typical pattern emerge. That is, the age old (and sometimes harsh)
rivalry between the English and the French, and the “luxury-model” tendency of
Scandinavia to come in to make the best one by choice (!)
Sources
Dreyer, J.L.E, A History of
Astronomy from Thales to Kepler (Dover :1953)
Pannekoek, A, A History of
Astronomy (Dover: 1962)
Wolf, A., A History
of Science Technology and Philosophy in the 16th and 17th Centuries (George
Allen & Unwin: 1963) (includes diagrams used in this article)
Equipment review...
Orion XT10 Intelliscope 4/11/04
10" f/ 4.7 Newtonian, 9X50 finder, 25 mm, 10 mm Plossls, $649 (+ $149 for
controller)
Ed Ting
I had good things to say
about the original XT10, but in late 2003 Orion surprised everyone by offering
an upgraded version of the scope with digital setting circles (the original XT10
is still available at a lowered price of $549.) In addition to the electronics,
the new Intelliscope version has a redesigned swoopy base, a gray tube instead
of black, new mirror cell with larger collimation screws, and a brand new
tensioning system (without the pulldown springs) for both axes. The new scope
weighs 2.5 lbs less than the old version. This may not seem like a lot, but at
the end of a cold, long observing session, you'll be grateful for every pound
saved.
The scope arrived in two
large cartons. It was missing the manual, allen key, and CD ROM. A quick phone
call to Orion remedied this, and the omissions in any case were not serious (the
manual is available online in case this happens to you by the way.) The
instructions were well-written, with lots of cautions, explanations, and photos.
The latter was especially useful when it came time to assemble the electronics.
Even if you don't buy the controller ($149) you still get the electronic pickups
for both axes, and the encoder wheel for the azimuth bearing (the encoder wheel
for the altitude axis comes with the controller.) All in all, assembly took
about 30 minutes.
The end result of all this?
The scope moves really well, as least as well as before, and now you've got
adjustable tension on the altitude axis. After a few minutes of observing, I got
used to the mechanics and nothing about the scope's design really jumped out at
me (a good sign.) The swoopy holes cut into the base board not only save
precious weight, they're handy as carrying handles. I was uncomfortable carrying
the original XT10 in one piece by myself, but the cutouts on the new version
make it easy for one person to transport the unit.
___________________________________________________________________
The optics on this unit are
very good, with only slight undercorrection. Cassini's Division on Saturn and
shadow transits on Jupiter are tack sharp in good conditions. The scope arrived
in time to hunt down galaxies in the Virgo Cluster, and the scope's nice 10"
aperture came inhandy when finding dimmer objects like the Siamese Twins (NGC
4567/4568) or the fainter members of Markarian's Chain. NGC 891 showed good
extension from my magnitude 5.0 skies.
The really big news,
however, is the Intelliscope controller, available separately for $149. There's
some minor assembly you have to do, which takes another 15 minutes or so if you
take your time. If you've initialized an Autostar, NexStar, Sky Tour, Sky
Wizard, Sky Commander, etc, before you'll have no trouble with this unit. Upon
power up, the controller asks you to level the scope, then you align two stars,
pressing "Enter" after each one. A couple of seconds later, the controller gives
you the amusingly-named "Warp Factor" which tells you how good a job you did. A
Warp Factor of .5 or less is said to be adequate for general use. Some typical
Warp Factors from my first session: .5, .5, 1.1, .4, .5. If these things catch
on, I can imagine Intelliscope owners bragging back and forth about their Warp
Factors in the observing field, to the befuddlement of other observers. By the
way, if you're feeling mischievous, like I was, you can try seeing how high you
can get the Warp Factor by purposely doing a bad alignment. I got it up to 30.3
once.
With a Warp Factor of .5 or
less (OK, now I'm doing it) the electronics are very accurate. I intentionally
swung the scope from one side of the sky to the other in an attempt to confuse
the electronics, but the accuracy remained. The scope refused to find Venus,
however. It would find objects near Venus, but when asked to find the planet, it
would consistently take me to a place about 10 degrees away. There are few other
quirks. Attempt to look at the Ghost of Jupiter planetary and the display reads
"Eye Nebula." Dial in M81 and the computer will read "Bode's Nebula," a
nomenclature I haven't seen used in decades.
The most controversial
aspect of the controller, however, is its self-described energy- saving feature.
If you don't touch any buttons for 15 minutes, it shuts itself off. If you want
to observe again, you have to power up the unit and go through the alignment
procedure all over again. Most active users will be hitting buttons within the
15 minute time period, but I don't like the idea of a meter running in the
background while I'm observing (especially if I've got a good Warp Factor dialed
in.) Also, if you take a break during a long session, you may come back to a
blank screen. Perhaps this could be addressed in an upcoming firmware upgrade.
The controller also has a host of other useful options and features, and I still
hadn't gotten to use them all before the review period was up.
Based on the amazing (and
often beautiful) XT-based rigs you've shown me, it's apparent that some of you
view the XT series the way a skilled painter looks at a blank canvas. It's not a
telescope, it's a means of self-expression. The Intelliscope will probably
continue to be a modkateer favorite, but use caution around the electronics.
Some have reported that a mod as simple as adding formica to the base board may
disable the encoder. Why? The thickness of the laminate moves the sensor too far
away from the encoder wheel. This will require you to sand or file the teflon
pads down to compensate. The moral: be careful, and think before you act.
The XT series continues to
be my favorite entry-level telescope line. They're well-made, robust, have good
optics and mechanics, and they're cheap. Since the non electronic versions are
back in the lineup, you have a choice. I like the new computer, but after a few
nights with it I went back to using the scope the old fashioned way (by hand.)
If you share my biases, the choice may come down to whether or not the
mechanical upgrades on the Intelliscope are worth the extra $100 or not. Your
choice.
(About the author: Ed Ting
has been reviewing astronomy equipment for years. He was recently published in
Night Sky Magazine. )
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