1 Logan Square
Philadelphia, Pennsylvania 19103
U.S.A.
History of Sun Distributors L.P.
Sun Distributors L.P. is a leading industrial distribution firm. The company sells more than 100,000 products and related services in three main areas of operation: fluid power, glass, and maintenance items. Sun's customers are located throughout the United States, Canada, and Mexico. Founded as a subsidiary of an oil company, the company was spun off into a limited partnership in the late 1980s, commencing a period of strong growth through acquisitions of other businesses in its industry.
Sun got its start in 1975, when the Sun Company, Inc., an oil company perhaps best known for its Sunoco gas stations, purchased a distributing business, which supplied equipment and other materials to a wide variety of industrial customers. With this move, Sun hoped to create a financial counter-balance to its highly cyclical petroleum businesses. Sun established Sun Distributors as a subsidiary, and the company began to acquire other properties in the distribution field.
In entering the distribution field, Sun moved into an industry in a state of flux. In the years before World War II, most industrial distribution businesses had emerged as very small "mom and pop" organizations, which resold equipment to a very small segment of one industry. Because they were tied to the single narrow market that they served, distributors saw their financial fates rise and fall with those of their customers. In the wake of World War II, however, many of these businesses started to grow and diversify their product offerings and target customer bases. With time, larger companies started to buy up smaller ones, as the industry consolidated, and Sun became part of that process.
In August 1976, Sun bought Walter Norris, a distributor of hydraulic and pneumatic controls. During this time, the company also announced that it would acquire Kar Products, Inc., a distributor of fastening systems. This purchase was completed in February 1977, when Sun paid $31.5 million for the property. In November of that year, Sun paid $10 million for Unibraze. At the end of 1977, Sun had sales of $20 million.
Sun's steady string of acquisitions continued in March 1978, when the company paid $3.6 million for the Atlas Screw & Specialty company. At the end of that year, Sun also bought the J.N. Fauver Company, a Canadian enterprise in the fluid power field.
In putting together a group of different companies, Sun sought to become a major player in the "value-added reseller" field, making the parts it provided to manufacturers more valuable and competitive through the level of service that went along with them. Traditionally, competitors in the distribution business had focused on price as the sole selling point for their goods, and the only way in which one company was differentiated from another. As manufacturing became more complex, however, the demands that customers made upon distributors also became more sophisticated, and service, which allowed industrial customers to work more effectively and efficiently, became just as important as price.
Although the products that Sun offered were relatively commonplace, the level of expertise that the company's various subsidiaries offered in addition to the parts themselves helped the company's offerings stand out in the marketplace. "They take over activities or functions performed by either the manufacturer or the customer and charge for them," one industry analyst explained to Forbes. In this way, Sun's operations strived to bridge the gap between the manufacturing economy and the service economy.
Sun continued to grow through acquisitions and diversify its operations in the early 1980s. In 1981, the company purchased the Special-T-Metals Company of Lawrence, Kansas. In late May 1985, Sun bought the Keathley-Patterson Electric Company, Inc.
By 1985, Sun Distributors had come to account for three percent of its parent company's revenues. In the following year, the Sun oil company decided to sell off its non-energy businesses, and the company announced that it was seeking a buyer for Sun Distributors in the late spring of 1986. Shortly after that, Sun augmented its holdings again, when the company bought the Air Draulics Company.
In August 1986, Sun announced that it would sell off its distributor business to a group of the subsidiary's executives, who joined with the investment bank Shearson Lehman Brothers to purchase the company in a leveraged buyout. In October, Shearson Lehman Brothers Holdings, Inc. bought Sun Distributor's capital stock for $199 million.
At that time, Sun also withdrew from one of the market segments in which it had been operating at a loss. The company sold its pipe and steel business, the Federal Pipe and Steel Corporation, taking a $1.5 million pretax loss in the process.
After Sun Distributors was acquired by Shearson Lehman Brothers, in January 1987, the company was reorganized as a master limited partnership. Shearson reportedly chose this corporate structure to take advantage of a temporary loophole in tax laws. At the time, tax rates for individuals were much lower than those for corporations. By setting up Sun Distributors as a master limited partnership, the investment bank enabled investors to apply losses against the company's profits, a practice otherwise impossible as a conventional corporation. At the end of ten years, Sun would be required to convert to a regular corporation and start paying corporate income taxes, or be sold.
In February 1987, all but one percent of the operating partnership of Sun Distributors was sold, in units priced at $10 each. Each unit consisted on one share of class A stock and one share of class B stock. Roughly 40 thousand of these units, or a quarter of the equity shares, were held by Sun's management, and more than ten million were sold to the general public. Because of Sun's status as a master limited partnership, and its two-tiered structure of stock offerings, investing in Sun became a complicated process for many potential stockholders.
Nevertheless, in the wake of its successful stock offering, Sun once again began to acquire companies. In July 1987, the company purchased the Warren Engineering Corporation, and by the end of the year, Sun's annual revenues had risen to $426 million, which generated nearly $19 million of operating income. However, because of costs associated with its separation for its parent company, and its establishment as a master limited partnership and initial offering of stock, the company posted a loss for the year of $6.6 million.
In February 1988, Sun also purchased the assets of Glass Related Products, Inc. By this time, Sun's string of acquisitions had made it one of the ten largest industrial distributors in the country. The company sought out entrepreneurial enterprises with strong management that put an emphasis on customer service. In addition, Sun had focused its activities on four fields: electrical supplies, such as light fixtures and cables; fluid power equipment for pneumatic and hydraulic systems; glass materials, for cars and mirrors; and maintenance products, such as cleaners, chemicals, nuts, and bolts. Within these areas, which encompassed 15 subsidiaries, Sun sold more than 100,000 different products.
Sun's customers ranged from original equipment manufacturers and users of replacement parts, to construction firms and maintenance companies. Increasingly, in the late 1980s, these operations turned to "just-in-time" processes, a more efficient method of manufacturing which sought to reduce the amount of money spent on inventory and replacement parts. In order to implement just-in-time processes, manufacturers relied on quick delivery of parts and special services. This created a market niche for Sun to fill, and the company worked to develop the capacity to make specialized production runs at short notice. Big manufacturers, Sun's chairperson, Donald Marshall, explained to Forbes, "can't make a pump and a motor with 20 valves out of 1,000 coming out sideways. They can't have salesmen running down to St. Joe to make a call on a guy who's going to spend $1,000 a year or wants a little design help. This creates an opening for us." All in all, Sun sought to sell the engineering and repair services that made its products better than those of its competitors.
Although, on the whole, Sun's strategy proved effective, there were some areas of operation that proved weak. For instance, the company found it difficult to make a profit on its sales of electrical supplies, and was also struggling in the sheet glass market, where it was consistently undercut by low-cost competitors. In an effort to alleviate this problem, Sun cut back on its operations in this area, concentrating instead on tinted, beveled, or mirrored glass. As part of this process, Sun purchased Glass Related Products, Inc., in February 1988.
In managing its constellation of 15 subsidiaries, Sun adopted a hands-off approach. Because the company only sought to buy well-managed companies, it refrained from tampering with operations that were doing well already. Instead, Sun provided capital for expansion and expertise in the systems needed to run a distribution business. Because of this low-interference policy, Sun was able to keep the size of its central headquarters staff quite low, and the company was overseen from Philadelphia by just 13 people: the company's chairman, four vice-presidents, four accountants, and four secretaries. Each of Sun's four operating groups was administered by a vice-president, accountant, and secretary.
To further emphasize the decentralized structure of Sun's corporate philosophy, managers of the company's subsidiaries were not summoned to Philadelphia to report to their superiors, but were visited at the site of their businesses by the company's president, who spent more than half of his year on the road. According to The Service Edge: 101 Companies that Profit from Customer Care, a book in which Sun Distributors was featured, Marshall told one Philadelphia business magazine that "behind our nearly half-billion in annual sales are thousands of employees who've built years-long relationships with thousands of customers. The surest way to destroy all of that would be for corporate-level staff to travel out there imposing a 'generic' model of the distribution business on each of the divisions."
After establishing its corporate independence and raising capital through its stock offering, Sun moved aggressively to further expand its business through the acquisition of successful companies in its four areas of concentration. In 1988, Sun purchased the Gem City Electric Company, Air-Dreco, Inc., E & B Electric Supply, Inc., and E & B Electric Supply of Crosset, Inc. Over the next two years, Sun also acquired the A & H Bolt and Nut Company, Limited, Edwards Engineering Corporation, and Industrial Air and Hydraulics, Inc. In July 1990, Sun divested itself of an asset, selling the property of the Atlas Screw & Specialty Company. As a result of its steady growth through mergers with small suppliers, Sun's revenues had grown to exceed $500 million by the time the company entered the 1990s.
At the start of the 1990s, however, Sun confronted a sharp drop in demand for many of the products it offered, as the industries it served felt the effects of economic recession. In response to these conditions, the company embarked upon a two-year program of cutting costs, adjusting the size of its operations, and maximizing its assets.
In addition, the company continued to make strategic acquisitions. In 1991, Sun purchased Hydra Power Systems, Rogers Wholesale Electric, Inc., and Activation, Inc. The following year, Sun's leaders sought to renegotiate the debt that the company had amassed through its acquisition spree and agreed to a moratorium on further acquisitions for the next two years.
By 1992, Sun's expectations for market recovery had proved overly optimistic. Therefore, management reassessed its plans and shifted the company's focus, in hopes of promoting further growth. Specifically, the company decided to become more proactive in seeking growth, rather than responding to fluctuating conditions within the market as a whole. Accordingly, Sun made some major changes in its traditional operations. In 1992, the company changed the way it paid presidents of its subsidiaries, setting up incentive programs for meeting sales goals. In addition, the company's headquarters staff became more involved in running the operations of its previously highly independent subsidiaries, to the extent that some operations were combined. Finally, Sun replaced the leaders of four troubled units, bringing in new managers.
In September 1992, frustrated by the restrictions imposed by the company's high debt load, and the financial constraints of its status as a master limited partnership, Sun's management announced that it had hired financial advisors to explore ways that the company's value could best be maximized. The options under consideration included a restructuring of the company, sale of certain selected assets, or liquidation of the entire company. The announcement that this process was being undertaken contributed immediately to a rise in the price of the company's stock.
By the start of 1993, Sun's efforts to restructure had helped to contribute to a record of steady growth. Net profits had grown 14 percent a year for the last five years, despite the fact that sales had only increased by six percent. Although the company's sales flattened somewhat in the first half of 1993, and earnings dipped, Sun's fortunes had revived by the end of the year, and sales reached $656 million, a new high. The company's managers attributed this growth to a re-emphasis on service and the exploration of new markets, a necessary alternative to growth through acquisition, banned until 1995.
Sun's returns remained strong in the first half of 1994, as innovative operations, like repair centers in the company's fluid power group, made strong contributions. In the fall of 1994, Sun announced that it had completed the process of internal re-evaluation of its assets and options. The company's managers stated that they had decided not to liquidate Sun's assets, but to shift the company's emphasis somewhat, shedding operations in one of its four main business areas. In October, the company announced that it would sell its three electrical group divisions, long a source of poor returns. The concerns to be sold included the American Electric Company, the Keathley-Patterson Electric Company, and Philips & Company. Sun also divested itself of Dorman Products, a subsidiary of its maintenance group.
With the proceeds of the this sale, which totaled $73 million, the company planned to pay down debts and finance further acquisitions. Sun also hoped to move away from the period of financial stricture which had governed its operations in the early 1990s. In November 1994, Sun appointed a new president and executive vice-president, John McDonnell, as the company readied itself for an aggressive policy of expansion in its remaining core businesses: fluid power, glass, and maintenance. "Our strategy has been to acquire well-managed distributors where the present ownership has reached an age to go on to retirement, or on to something else, and there is no apparent succession in the family," McDonnell told the Philadelphia Enquirer.
In addition, Sun planned to step up its burgeoning operations in Mexico. The company did a brisk business supplying manufacturing plants that had sprung up just over the border, and also planned to begin operations in central Mexico. As Sun moved into the late 1990s, its three remaining operating units appeared strong, and its status as a major player in the distribution field appeared secure.
Principal Subsidiaries: S.D.I. Operating Partners, L.P.
Related information about Sun
The central object of our Solar System and the nearest star to
the Earth. Its basic characteristics are: mass
99×1030 kg; radius
696 000 km/432 500 mi; mean density
4 g/cm3; mean rotation period 2 4 days; luminosity
85×1024 J/s. Its average distance from Earth is 150
million km/93 million mi, and on account of this
proximity it is studied more than any other star. The source of its
energy is nuclear reactions in the central core (temperature 15
million K, relative density 155) extending to a quarter of the
solar radius and including half the mass. Our Sun is nearly 5000
million years old, and is about halfway through its expected
life-cycle. Every second it annihilates 5 million tonnes of matter,
to maintain power output of
39 × 1026 watts of energy.otheruses
Observation
data
|
Mean distance from
Earth
|
149.6 km
(92.95 mi)
(8.31 minutes at the speed of light)
|
Visual brightness (V)
|
−26.8m
|
Absolute magnitude
|
4.8m
|
Spectral classification
|
G2V
|
Orbital
characteristics
|
Mean distance from
Milky Way
core
|
17}} km
(26,000-28,000 light-years)
|
Galactic period
|
8}} a |
Velocity
|
217 km/s
orbit around the center of the Galaxy, 20 km/s relative to
average velocity of other stars in stellar
neighborhood
|
Physical
characteristics
|
Mean diameter
|
1.392 km
(109 Earth diameters)
|
Circumference
|
4.373 km
(342 Earth diameters)
|
Oblateness
|
−6}}
|
Surface area
|
6.09 km²
(11,900 Earths)
|
Volume
|
1.41 km³
(1,300,000 Earths)
|
Mass
|
30}} kg(332,946 Earths)
|
Density
|
1.408 g/cm³
|
Surface gravity
|
273.95 m s-2
(27.9 g)
|
Escape velocity
from the surface
|
617.54 km/s
(55 Earths)
|
Surface temperature
|
5785 K
|
Temperature of corona
|
5 MK
|
Core temperature
|
~13.6 MK
|
Luminosity (Lsol)
|
26}} W~9 cd[[cite journal
|
last=Menat
|
first=M.
|
year=1980
|
month=10
|
url=adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1980ApOpt..19.3458M&db_key=AST&data_type=HTML&format=&high=44b52c369030002 |
title=Atmospheric phenomena before and during
sunset
|
journal=Applied Optics
|
volume=19
|
27]] cd (V band)
(~100 lm/W
efficacy)
|
Mean Intensity (Isol)
|
7}} W m-2sr-1
|
Rotation
characteristics
|
Obliquity
|
7.25 °
(to the ecliptic)
67.23°
(to the galactic
plane)
|
Right ascension
of North pole[[cite web
|
url=www.hnsky.org/iau-iag.htm |
title=Report Of The IAU/IAG Working Group On Cartographic
Coordinates And Rotational Elements Of The Planets And
Satellites: 2000
|
accessdate=2006-03-22
|
first=P. Thomas
|
year=2000]] |
286.13°
(19 h 4 min 30 s)
|
Declination
of North pole
|
+63.87°
(63°52' North)
|
Rotation period
at equator
|
25.3800 days
(25 d 9 h 7 min 13 s)
|
Rotation velocity
at equator
|
7174 km/h
|
Photospheric composition
(by mass)
|
Hydrogen
|
73.46 %
|
Helium
|
24.85 %
|
Oxygen
|
0.77 %
|
Carbon
|
0.29 %
|
Iron
|
0.16 %
|
Neon
|
0.12 %
|
Nitrogen
|
0.09 %
|
Silicon
|
0.07 %
|
Magnesium
|
0.05 %
|
Sulphur
|
0.04 %
|
The Sun is the star
of our solar
system. The Earth and other matter (including other planets, asteroids, meteoroids, comets and dust) orbit the Sun, which by itself accounts for more than
99% of the solar system's mass. Energy
from the Sun?in the form of insolation from sunlight?supports almost all life on Earth via photosynthesis, and
drives the Earth's climate and weather.
The Sun is sometimes referred to by its Latin name Sol or by its Greek name Helios. Its astrological and astronomical symbol is a circle with a point at its
center: bigodot.
The sun's history and destiny
The Sun is about 4.6 billion years old and is about halfway
through its main-sequence evolution, during which nuclear fusion
reactions in its core fuse hydrogen into helium. Each second, more
than 4 million tonnes of matter are converted into energy within
the Sun's core, producing neutrinos and solar radiation.
In about 5 billion years, the Sun will evolve into a red giant and then a white dwarf, creating a
planetary
nebula in the process. The Sun's magnetic field gives rise to
many effects that are collectively called solar activity,
including sunspots on
the surface of the Sun, solar flares, and variations in the solar wind that carry
material through the solar system. The effects of solar activity on
Earth include auroras at moderate to high latitudes, and the
disruption of radio communications and electric power. Solar
activity is thought to have played a large role in the formation and evolution of
the solar system,
and strongly affects the structure of Earth's outer atmosphere.
Although it is the nearest star to Earth and has been intensively
studied by scientists, many questions about the Sun remain
unanswered, such as why its outer atmosphere has a temperature of
over a million K while
its visible surface (the photosphere) has a temperature of less than 6,000 K.
Current topics of scientific inquiry include the sun's regular
cycle of sunspot
activity, the physics and origin of solar flares and prominences, the
magnetic interaction between the chromosphere and the corona, and the origin of the solar wind.
Overview
About 74% of the Sun's mass is hydrogen, 25% is helium, and the rest is made up of trace quantities of
heavier elements. "G2" means that it has a surface temperature of
approximately 5,500 K, giving it a white color, which
because of atmospheric scattering appears yellow. This means that it generates
its energy by nuclear
fusion of hydrogen
nuclei into helium and is
in a state of hydrostatic balance, neither contracting nor expanding
over time. Because of logarithmic size distribution, the Sun is
actually brighter than 85% of the stars in the Galaxy, most of
which are red dwarfs.
www.space.com/scienceastronomy/060130_mm_single_stars.html
The Sun orbits the center of the Milky Way galaxy at a distance of about 25,000 to 28,000 light-years from the galactic center,
completing one revolution in about 225?250 million years. The orbital speed is
217 km/s, equivalent to one light-year every 1,400 years, and
one AU every 8
days.
The Sun is a third generation star, whose formation may have been
triggered by shockwaves from a nearby supernova. This is suggested by a high abundance of heavy elements such as
gold and uranium in the solar system;
these elements could most plausibly have been produced by endergonic nuclear reactions
during a supernova, or by transmutation via neutron absorption inside a massive second-generation
star.
Sunlight is the main source of energy near the surface of Earth.
Sunlight on the surface of Earth is attenuated by the Earth's atmosphere so that less power
arrives at the surface—closer to 1,000 watts per directly
exposed square meter in clear conditions when the Sun is near the
zenith. This energy can
be harnessed via a variety of natural and synthetic
processes—photosynthesis by plants captures the energy of sunlight
and converts it to chemical form (oxygen and reduced carbon
compounds), while direct heating or electrical conversion by
solar cells are used
by solar power
equipment to generate electricity or to do other useful work. The energy
stored in petroleum
and other fossil
fuels was originally converted from sunlight by photosynthesis
in the distant past.
Sunlight has several interesting biological properties. Ultraviolet light from the
Sun has antiseptic
properties and can be used to sterilize tools. It also causes
sunburn, and has other
medical effects such as the production of Vitamin D. Its current age,
determined using computer models of stellar evolution and nucleocosmochronology, is thought to be about 4.57
billion years.
The Sun does not have enough mass to explode as a supernova. The Sun is a
near-perfect sphere, with
an oblateness
estimated at about 9 millionths, which means that its polar
diameter differs from its equatorial diameter by only 10 km.
While the Sun does not rotate as a solid body (the rotational
period is 25 days at the equator and about 35 days at the poles), it takes approximately 28 days to complete
one full rotation; Tidal effects from the planets do not
significantly affect the shape of the Sun, although the Sun itself
orbits the center of
mass of the solar system, which is located nearly a solar
radius away from the center of the Sun mostly because of the large
mass of Jupiter.
The Sun does not have a definite boundary as rocky planets do; This
is simply the layer below which the gases are thick enough to be
opaque but above which
they are transparent; Most of the Sun's mass lies within about
0.7 radii of the
center.
The solar interior is not directly observable, and the Sun itself
is opaque to electromagnetic radiation. However, just as seismology uses waves
generated by earthquakes to reveal the interior structure of the
Earth, the discipline of helioseismology makes use of pressure waves (infrasound) traversing the
Sun's interior to measure and visualize the Sun's inner structure.
Energy is produced by exothermic thermonuclear reactions (nuclear fusion) that
mainly convert hydrogen
into helium, helium into carbon, carbon into iron. All of the energy produced by fusion in the core
must travel through many successive layers to the solar photosphere
before it escapes into space as sunlight or kinetic energy of particles.
About 8.9 protons
(hydrogen nuclei) are converted into helium nuclei every second,
releasing energy at the matter-energy conversion rate of 4.26
million tonnes per second, 383 yottawatts (383 W) or 9.15 megatons of TNT per second. The rate of nuclear fusion depends
strongly on density, so the fusion rate in the core is in a
self-correcting equilibrium: a slightly higher rate of fusion would
cause the core to heat up more and expand slightly
against the weight of the
outer layers, reducing the fusion rate and correcting the perturbation; and a
slightly lower rate would cause the core to cool and shrink
slightly, increasing the fusion rate and again reverting it to its
present level.
The high-energy photons
(gamma and X-rays) released in fusion reactions take a long time to
reach the Sun's surface, slowed down by the indirect path taken, as
well as by constant absorption and reemission at lower energies in
the solar mantle. For many years measurements of the number of
neutrinos produced in the Sun were much lower than
theories predicted, a problem which was recently resolved
through a better understanding of the effects of neutrino
oscillation. while the material grows cooler as altitude
increases, this temperature gradient is slower than the adiabatic lapse
rate and hence cannot drive convection. Heat is transferred by
radiation—ions of hydrogen and helium emit
photons, which travel a
brief distance before being reabsorbed by other ions. Convective
overshoot is thought to occur at the base of the convection
zone, carrying turbulent downflows into the outer layers of the
radiative zone.
The thermal columns in the convection zone form an imprint on the
surface of the Sun, in the form of the solar
granulation and supergranulation. Sunlight has approximately a black-body spectrum that
indicates its temperature is about 6,000 K (10,340°F / 5,727 °C), interspersed with
atomic absorption
lines from the tenuous layers above the photosphere. The
photosphere has a particle density of about
1023 m−3 (this is about 1% of the
particle density of Earth's atmosphere at sea level).
During early studies of the optical spectrum of the photosphere, some
absorption lines were found that did not correspond to any chemical elements then
known on Earth. In 1868, Norman Lockyer hypothesized that these absorption lines
were because of a new element which he dubbed "helium", after the Greek Sun god
Helios. They can be
viewed with telescopes operating across the electromagnetic
spectrum, from radio through visible light to gamma rays, and comprise five principal zones: the
temperature minimum, the chromosphere, the transition
region, the corona,
and the heliosphere.
The heliosphere, which may be considered the tenuous outer
atmosphere of the Sun, extends outward past the orbit of Pluto to the heliopause, where it forms a
sharp shock front
boundary with the interstellar medium. The increase is because of a
phase
transition as helium
within the region becomes fully ionized by the high temperatures. Rather, it forms a
kind of nimbus around
chromospheric features such as spicules and filaments, and is in constant, chaotic motion. The
transition region is not easily visible from Earth's surface, but
is readily observable from space by instruments sensitive to the far ultraviolet portion of
the spectrum.
The corona is the extended outer atmosphere of the Sun, which is
much larger in volume than the Sun itself. The corona merges
smoothly with the solar
wind that fills the solar system and heliosphere. While no complete theory yet exists to
account for the temperature of the corona, at least some of its
heat is known to be from magnetic reconnection.
The heliosphere
extends from approximately 20 solar radii (0.1 AU) to the
outer fringes of the solar system. Its inner boundary is defined as
the layer in which the flow of the solar wind becomes superalfvénic—that is,
where the flow becomes faster than the speed of Alfvén waves. The solar wind
travels outward continuously through the heliosphere, forming the
solar magnetic field into a spiral shape, until it impacts the heliopause more than 50 AU
from the Sun. In December 2004, the Voyager 1 probe passed
through a shock
front that is thought to be part of the heliopause. The
magnetic field gives rise to strong heating in the corona, forming
active regions
that are the source of intense solar flares and coronal mass ejections. The polarity of the
leading sunspot alternates every solar cycle, so that it will be a
north magnetic pole in one solar cycle and a south magnetic pole in
the next.
The solar cycle has a great influence on space weather, and seems
also to have a strong influence on the Earth's climate. During this
era, which is known as the Maunder minimum or Little Ice Age, Europe experienced very cold
temperatures. Earlier extended minima have been discovered through
analysis of tree rings
and also appear to have coincided with lower-than-average global
temperatures. The Van Allen belts consist of an inner belt composed
primarily of protons and
an outer belt composed mostly of electrons. The most energetic particles can 'leak out'
of the belts and strike the Earth's upper atmosphere, causing
auroras, known as aurorae borealis in the northern
hemisphere and aurorae australis in the southern hemisphere.
In periods of normal solar activity, aurorae can be seen in
oval-shaped regions centered on the magnetic poles and lying roughly at a geomagnetic
latitude of 65°, but at times of high solar activity the
auroral oval can expand greatly, moving towards the equator.
Theories proposed to resolve the problem either tried to reduce the
temperature of the Sun's interior to explain the lower neutrino
flux, or posited that electron neutrinos could oscillate, that is,
change into undetectable tau and muon neutrinos as they traveled between the Sun and the
Earth. Several neutrino observatories were built in the 1980s to
measure the solar neutrino flux as accurately as possible,
including the Sudbury Neutrino Observatory and Kamiokande.
Coronal heating problem
The optical surface of the Sun (the photosphere) is known to
have a temperature of approximately 6,000 K. The other is magnetic heating, in which magnetic energy is
continuously built up by photospheric motion and released through
magnetic
reconnection in the form of large solar flares and myriad similar but smaller
events.
Currently, it is unclear whether waves are an efficient heating
mechanism.
Faint young sun problem
Theoretical models of the sun's development suggest that 3.8 to 2.5
billion years ago, during the Archean period, the Sun was only about 75% as bright as
it is today. The general consensus among scientists is that the
young Earth's atmosphere contained much larger quantities of
greenhouse gases
(such as carbon
dioxide and/or ammonia) than are present today, which trapped enough
heat to compensate for the lesser amount of solar energy reaching
the planet.
Magnetic field
All matter in the Sun
is in the form of gas and
plasma
because of its high temperatures. The differential rotation of
the Sun's latitudes causes its magnetic field lines to become twisted together
over time, causing magnetic field loops to erupt from the Sun's
surface and trigger the formation of the Sun's dramatic sunspots and solar prominences (see
magnetic
reconnection). This twisting action gives rise to the solar dynamo and an 11-year
solar cycle of
magnetic activity as the Sun's magnetic field reverses itself about
every 11 years.
The influence of the Sun's rotating magnetic
field on the plasma in the interplanetary
medium creates the heliospheric current sheet, which separates
regions with magnetic fields pointing in different directions.
Magnetohydrodynamic (MHD) theory predicts that the
motion of a conducting fluid (e.g., the interplanetary medium) in a
magnetic field, induces electric currents which in turn generates
magnetic fields, and in this respect it behaves like an MHD dynamo.
History of solar observation
Early understanding of the Sun
Humanity's most fundamental understanding of the Sun is as the
luminous disk in the heavens, whose presence above the horizon creates day and whose
absence causes night. In many prehistoric and ancient cultures, the
Sun was thought to be a solar deity or other supernatural phenomenon, and worship of the Sun was
central to civilizations such as the Inca of South America and the Aztecs of what is now Mexico. for example, stone megaliths accurately mark the summer solstice (some of
the most prominent megaliths are located in Nabta Playa, Egypt, and at Stonehenge in England); the pyramid of
El
Castillo at Chichén Itzá in Mexico is designed to cast shadows in
the shape of serpents climbing the pyramid at the vernal and autumn
equinoxes. With respect
to the fixed stars,
the Sun appears from Earth to revolve once a year along the
ecliptic through the
zodiac, and so the Sun
was considered by Greek astronomers to be one of the seven planets (Greek planetes,
"wanderer"), after which the seven days of the week are named in some
languages.
Development of modern scientific understanding
One of the first people in the Western world to offer a
scientific explanation for the sun was the Greek philosopher Anaxagoras, who reasoned that
it was a giant flaming ball of metal even larger than the Peloponnesus, and not the
chariot of Helios. For teaching this
heresy, he was imprisoned
by the authorities and sentenced to death (though later released through the
intervention of Pericles). In the early 17th century, Galileo pioneered telescopic observations of the
Sun, making some of the first known observations of sunspots and
positing that they were on the surface of the Sun rather than small
objects passing between the Earth and the Sun. Isaac Newton observed the
Sun's light using a prism,
and showed that it was made up of light of many colors, while in
1800 William
Herschel discovered infrared radiation beyond the red part of the solar
spectrum. The 1800s saw spectroscopic studies of the Sun advance,
and Joseph von
Fraunhofer made the first observations of absorption lines in the
spectrum, the strongest of which are still often referred to as
Fraunhofer lines.
In the early years of the modern scientific era, the source of the
Sun's energy was a significant puzzle. Lord Kelvin suggested that
the Sun was a gradually cooling liquid body that was radiating an
internal store of heat. Kelvin and Hermann von
Helmholtz then proposed the Kelvin-Helmholtz
mechanism to explain the energy output. Ernest Rutherford
suggested that the energy could be maintained by an internal source
of heat, and suggested radioactive decay as the source. However it would be
Albert Einstein
who would provide the essential clue to the source of a Sun's
energy with his mass-energy relation E=mc².
In 1920 Sir Arthur
Eddington proposed that the pressures and temperatures at the
core of the Sun could produce a nuclear fusion reaction that merged
hydrogen into helium, resulting in a production of energy from the
net change in mass. This theoretical concept was developed
in the 1930s by the astrophysicists Subrahmanyan
Chandrasekhar and Hans Bethe.
Solar space missions
The first satellites designed to observe the Sun were NASA's Pioneers 5, 6, 7, 8 and
9, which were launched between 1959 and 1968. Pioneer 9 operated
for a particularly long period of time, transmitting data until
1987.
In the 1970s, Helios
1 and the Skylab
Apollo
Telescope Mount provided scientists with significant new data
on solar wind and the solar corona. The Helios 1 satellite was a
joint U.S.-German probe that studied the solar wind from an
orbit carrying the spacecraft inside Mercury's orbit at
perihelion.
Discoveries included the first observations of coronal mass
ejections, then called "coronal transients", and of coronal holes, now known to
be intimately associated with the solar wind.
In 1980, the Solar Maximum Mission was launched by NASA. This spacecraft was designed
to observe gamma rays,
X-rays and UV radiation from solar flares during a time
of high solar activity. In 1984 Space Shuttle Challenger mission STS-41C retrieved the satellite and
repaired its electronics before re-releasing it into orbit. The
Solar Maximum Mission subsequently acquired thousands of images of
the solar corona before re-entering the Earth's atmosphere in June 1989.
Japan's Yohkoh (Sunbeam)
satellite, launched in 1991, observed solar flares at X-ray
wavelengths. It was destroyed by atmospheric reentry in 2005.
One of the most important solar missions to date has been the
Solar and Heliospheric Observatory, jointly built by the
European Space
Agency and NASA and
launched on December
2, 1995. In addition to
its direct solar observation, SOHO has enabled the discovery of
large numbers of comets, mostly very tiny sungrazing comets which
incinerate as they pass the Sun.
All these satellites have observed the Sun from the plane of the
ecliptic, and so have only observed its equatorial regions in
detail. Once Ulysses was in its scheduled orbit, it began observing
the solar wind and magnetic field strength at high solar latitudes,
finding that the solar wind from high latitudes was moving at about
750 km/s (slower than expected), and that there were large
magnetic waves emerging from high latitudes which scattered
galactic cosmic
rays.
Elemental abundances in the photosphere are well known from
spectroscopic studies, but the composition of the
interior of the Sun is more poorly understood. A solar wind sample return
mission, Genesis, was designed to allow astronomers to directly
measure the composition of solar material. Genesis returned to
Earth in 2004 but was
damaged by a crash landing after its parachute failed to deploy on reentry into Earth's
atmosphere. UV
exposure gradually yellows the lens of the eye over a period of
years and can cause cataracts, but those depend on general exposure to solar
UV, not on whether one looks directly at the Sun.
When looking at the sun, either with or without optical aid, using
a proper filter is important as some improvised filters pass UV or
IR rays that can damage the eye at high brightness levels. For
example, any kind of photographic color film transmits IR light and
must not be used.
Viewing the Sun through light-concentrating optics such as binoculars is very hazardous
without an attenuating (ND) filter to dim the sunlight. These
filters can be made of mirrored glass or metallised plastic
film.
Partial solar
eclipses are hazardous to view because the eye's pupil is not adapted to the
unusually high visual contrast: the pupil dilates according to the
total amount of light in the field of view, not by the
brightest object in the field. This can damage or kill those cells,
resulting in small permanent blind spots for the viewer. The hazard
is insidious for inexperienced observers and for children, because
there is no perception of pain: it is not immediately obvious that
one's vision is being destroyed.
During sunrise and
sunset, sunlight is
attenuated through rayleigh and mie scattering of light by a particularly long passage
through Earth's atmosphere, and the direct Sun is sometimes faint
enough to be viewed directly without discomfort or safely with
binoculars (provided there is no risk of bright sunlight suddenly
appearing in a break between clouds).
See also
- List of Solar System bodies formerly considered
planets
- Formation and evolution of the solar
system
References
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