31700 Middlebelt Road, Suite 145
Farmington Hills, Michigan 48334
Sun Communities is committed to being the premier provider of quality community lifestyles by offering individualized housing and residential services. We aspire to be the industry leader in meeting the unique wants and needs of our customers. We dedicate ourselves to excellence by acting with integrity and honesty, exploring new revenue sources, emphasizing caring and fairness, encouraging the entrepreneurial spirit, providing accountability through specialization, and fostering teamwork.
History of Sun Communities Inc.
Sun Communities Inc. operates as a real estate investment trust (REIT) that owns, operates, and develops manufactured housing communities. In 2001, the company had over 110 communities with over 39,000 developed sites and nearly 5,000 sites available for development. Sun's manufactured communities typically maintain an occupancy level of nearly 95 percent and have an average monthly rent of $288 per site. The firm operates in 15 states with the majority of sites in Michigan, Florida, Indiana, Ohio, and Texas.
Origins and the Escalating Popularity of the REIT
Milton M. Shiffman began investing in real estate in 1964. Working at the time as a doctor, Shiffman was involved in the development, acquisition, and construction of commercial property in his spare time. In 1975, he established the predecessor to Sun Communities Inc.
In 1981, Shiffman retired from his medical practice to concentrate fully on his growing company. He and his son, Gary A. Shiffman, began focusing on acquiring and then either expanding or renovating manufactured housing communities. In 1985, the pair incorporated the firm in order to pursue further growth options.
During the late 1980s, however, the real estate industry began to experience a decline. In fact, by the early 1990s, commercial property values dropped from between 30 and 50 percent. As a consequence, the Shiffmans began toying with the idea of launching a real estate investment trust. Congress created the REIT in 1960 to enable small investors to take a stake in large real estate investments. REITs were designed to pool the resources of many investors into a single entity that was focused on producing income through commercial real estate ownership and finance. Ninety percent of a REIT's taxable income was then paid out to its shareholders each year.
REITs did not become popular until the early 1990s, however, because of certain tax and ownership restrictions. At first, a REIT could only own real estate, but the Tax Reform Act of 1986 laid the groundwork for change and enabled a REIT to own, operate, and even finance income-producing real estate. The Act also restricted the use of real estate investments as tax shelters. When REITs were created, laws in the U.S. allowed taxpayers to take significant interest and depreciation deductions that reduced their taxable income. REITs on the other hand, were based on creating taxable income. Up until the Reform Act--which limited the amount an investor could deduct on their taxes--REITs had difficulty securing capital because many investors looked for tax-sheltering investment opportunities.
During the early 1990s, many private real estate companies began utilizing the REIT structure to gain capital. At the same time, investors also began to eye the commercial real estate industry as a lucrative investment and were confident that the market would recover from the troubles of the 1980s.
Going Public as a REIT: 1993
The Shiffman's followed suit and in December 1993 took Sun Communities Inc. public as a REIT, offering 5.7 million common shares. At the time of the initial public offering (IPO), the company operated 31 manufactured communities with 9,036 sites in six states.
Sun Communities began expanding rapidly after its IPO, which raised $145.8 million. In January 1994, it acquired Timberline Estates, a manufactured community with 296 sites located near Grand Rapids, Michigan. In March, the firm purchased Meadow Lake Estates for $12 million, increasing the number of its Michigan-based holdings to twelve.
By July of that year, Sun had acquired seven more communities and set plans in motion to sell an additional 3.5 million shares of its common stock. Chateau Properties Inc., a competing REIT based in Clinton Township, Michigan, took notice of Sun's activities. According to Crain's Detroit Business, Jeffrey Kellogg, CEO of the competitor, "speculated that Sun Communities maybe figured out they're not big enough and wanted to hurry up and grow while REITs are still popular with investors." Kellogg also stated in the 1994 article that there was "a certain amount of do-it-while-you-can philosophy" among REITs.
That philosophy certainly held true for Sun, who by the end of 1994 had the best-performing stock among manufactured housing REITs--Chateau Properties' stock was second in the ranking. In its first year of operating as a public REIT, Sun had acquired 15 properties for $92 million, and had expanded into Florida and St. Louis, Missouri. It also secured revenues of $32.3 million, and net income of $7.8 million.
Expansion and Acquisition: Mid- to Late 1990s
Sun continued to expand in 1995, adding 3,900 new sites to its arsenal. In April of that year, the firm acquired Scio Farms of Ann Arbor, Michigan, for $23.6 million. At the time, Scio--with 853 sites--was the largest single community that Sun had ever acquired. Sun then went on to purchase Kensington Meadows, also located in Michigan. The company funded the deal through the issuance of 51,678 operating partnership units (O.P. Units). This was the company's fifth purchase using O.P Units. In a 1995 company press release, president Gary Shiffman explained the benefits of the units, stating, "The issuance of O.P. units creates opportunities to acquire quality communities that would not otherwise be available because of tax ramifications to the seller. In addition, Sun has the ability to fund acquisitions without the costs associated with raising equity in the public marketplace."
During the mid-1990s, manufactured housing was the fastest-growing segment of the U.S. real estate industry. Investors were encouraged by their financial planners to buy shares in manufactured housing REITs, leaving Sun well positioned for continued growth. In fact, by the close of 1995, Sun had acquired two new communities in Florida and as well as two in Austin, Texas, which was considered the fastest growing area in the state in terms of population and job creation. Revenues for the year increased by 39 percent to $45.1 million, while net income reached $11.7 million.
Sun became involved in significant merger activity in 1996. In March of that year, the company announced plans to purchase 25 new manufactured housing communities from Aspen Enterprises Ltd. The $226 million deal increased Sun's holdings by nearly 60 percent, secured the company's hold on the Michigan market, and expanded the firm's reach in both the Florida and Arizona markets.
Acting as a white knight, Sun made an $380 million stock offer for competitor Chateau Properties in August 1996. Two days before Sun's bid, Chateau had received a hostile $387 million cash bid from Manufactured Home Communities Inc. (MHC). At the time of the offers, Chateau had plans in the works to merge with ROC Communities Inc. A merger of Sun and Chateau however, would secure Sun's position as the largest community owner in the United States, as well as rescue Chateau from the MCH bid--Chateau management felt a deal with MCH would not be beneficial for the firm.
While many analysts felt that both companies had offered too much for the Chateau--Sun's bid was the highest tax-free offer--the firms argued that it was a lucrative opportunity to get a step ahead of competition in the industry. During the mid-1990s, the industry was filled with companies that owned a relatively small amount of communities. In fact, "manufactured housing companies say they have no choice but to acquire each other because it is getting harder to find large groups of property for sale," reported The New York Times in August 1996.
The bids made by both Sun and MHC also marked the first unsolicited offers made among manufactured housing REITs. In the end though, Chateau opted to merge with ROC. The deal created the largest manufactured home community REIT in the United States.
Despite its failed attempt to acquire its largest competitor, Sun continued to expand and, by the end of 1996, operated 79 communities. Its revenue increased again, reaching $73.2 million, up 62 percent over the previous year. The company's net income also rose to $18.6 million.
The firm continued its acquisition strategy in 1997, with the purchase of nine communities from Park Realty Inc. for approximately $93 million. The deal strengthened Sun's foothold in the Southwest, Indiana, and Florida. Throughout the year, Sun acquired a total of 14 communities and developed 917 new sites. Through its Sun Home Services subsidiary, the company also sold 548 new homes and was involved in the resale brokerage of 555 additional homes. Sun also spun off Bingham Financial Services Corp. in 1997 as a financial services firm that offered financing and insurance to Sun's residents.
Revenues continued to grow in 1998, reaching $120.6 million. The company acquired ten communities that year, bringing its holdings to 106 communities. During 1999, Sun partnered with Champion Development Corp., a subsidiary of Champion Enterprises Inc., to develop manufactured housing communities in new growth markets. Operating under the name SunChamp, the venture developed nine communities in Texas, North
Continued Success in an Unstable Market
During its first six years of operating as a public REIT, Sun experienced good fortune. The company's earnings grew at an average annual growth rate of 10 percent. Its acquisition record was strong, homesite demand was high, and finance companies eased up on lending restrictions, allowing more people to finance homes. In fact, homes were selling at a record pace and according to the company, nearly 20 million people in the United States lived in manufactured housing, representing eight percent of the American population.
During 2000, however, the manufactured housing industry began to experience a decline. Finance companies had set credit standards too low during the 1990s and were now stuck with unpaid loans as well as repossessed homes. Many lenders then raised credit qualifications, leaving many buyers unable to obtain home loans. With the flood of repossessed homes on the market, sales of new homes began to falter and the number of new manufactured home buyers dropped.
While Sun's growth slowed during 2000, the company still recorded positive revenues of $134.4 million and net income of $29.1 million. The firm acquired three new communities that year and developed 751 new sites. It sold five slow growth communities in Florida as part of its strategy to focus on those communities with stronger earnings potential. Sun also launched its "Residents First" program, which was designed to improve its customer relations, reduce turnover in communities, attract new residents, and create demand for Sun properties. Founder Milton M. Shiffman died that year while son Gary remained at the helm of Sun as chairman and CEO.
Even as the manufactured home market remained unstable in 2001, Sun's future continued to look promising. The company's favorable occupancy levels and low tenant turnover coupled with a strong balance sheet left it well positioned for future growth. Shiffman commented in the company's 2000 annual report, "When the economic wind shifts from your back into your face, you must work harder and smarter to achieve your objectives." Sun management pledged to do just that in order to secure the firm's position as a leading owner and operator of manufactured housing communities.
Principal Subsidiaries: SCF Manager Inc.; SCN Manager Inc.; Sun Acquiring Inc.; Sun Florida QRS Inc.; Sun Houston QRS Inc.; Sun QRS Inc.; Sun Texas QRS Inc.; Sun Communities Operating Limited Partnership.
Principal Competitors: Chateau Communities Inc.; Manufactured Home Communities Inc.
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
|Mean distance from
(8.31 minutes at the speed of light)
|Visual brightness (V)
|Mean distance from
orbit around the center of the Galaxy, 20 km/s relative to
average velocity of other stars in stellar
(109 Earth diameters)
(342 Earth diameters)
|30}} kg(332,946 Earths)
|273.95 m s-2
from the surface
|Temperature of corona
|26}} W~9 cd[[cite journal
||title=Atmospheric phenomena before and during
|27]] cd (V band)
|Mean Intensity (Isol)
|7}} W m-2sr-1
(to the ecliptic)
(to the galactic
of North pole[[cite web
||title=Report Of The IAU/IAG Working Group On Cartographic
Coordinates And Rotational Elements Of The Planets And
(19 h 4 min 30 s)
of North pole
(25 d 9 h 7 min 13 s)
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
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
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.
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.
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
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
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
The Sun does not have enough mass to explode as a supernova. The Sun is a
near-perfect sphere, with
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
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
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
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
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
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 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.
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
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 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
reconnection in the form of large solar flares and myriad similar but smaller
Currently, it is unclear whether waves are an efficient heating
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
(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
All matter in the Sun
is in the form of gas and
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
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
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
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
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
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
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
In the 1970s, Helios
1 and the Skylab
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
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
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
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
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
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).
- List of Solar System bodies formerly considered
- Formation and evolution of the solar
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