A handle-shaped cloud of plasma erupts from the Sun.
Sun:
Our solar system's star, the Sun, has inspired mythological stories
in cultures around the world, including those of the ancient
Egyptians, the Aztecs of Mexico, Native American tribes of North
America and Canada, the Chinese, and many others. A number of ancient
cultures built stone structures or modified natural rock formations
to observe the Sun and Moon, they charted the seasons, created
calendars, and monitored solar and lunar eclipses. These
architectural sites show evidence of deliberate alignments to
astronomical phenomena: sunrises, moonrises, moonsets, even stars or
planets.
The Sun is the closest star to Earth, at a mean distance from our
planet of 149.60 million kilometers (92.96 million miles). This
distance is known as an astronomical unit (abbreviated AU), and sets
the scale for measuring distances all across the solar system. The
Sun, a huge sphere of mostly ionized gas, supports life on Earth. It
powers photosynthesis in green plants, and is ultimately the source
of all food and fossil fuel. The connection and interactions between
the Sun and Earth drive the seasons, ocean currents, weather, and
climate.
The companion to 51 Pegasi was the first planet discovered orbiting a
normal, Sun-like star beyond our solar system.
Beyond Our Solar System:
In 1991, the worlds of our own solar system were the only known
planets. Astronomers did not believe that our Sun's environment was
the only planet producer in the universe. But they had no evidence of
planets outside our solar system.
How quickly things change.
In 1991 radio astronomers detected the first extrasolar planets
orbiting a dying pulsar star. Although the deadly radiation from the
pulsar would not sustain life, it was the first example of a star
other than our Sun producing planets.
Since then more than 100 planets have been found orbiting other
stars. Some of them are orbiting extremely close to their parent star
like the 51 Pegasi planetary system, while others are found to be at
distances comparable to where Mars and Jupiter orbit in our solar
system.
Plans for Continued Searches
The right size, the right distance, the right temperature: we finally
have evidence for the existence of extrasolar worlds that may be
candidates for life-bearing planets as well. A search of the nearest
1,000 stars to our Sun may reveal evidence of planets very much like
Earth. "Earth-type" planets, the most conducive to sustaining life,
must be solid bodies (unlike the gas giant planets in our outer solar
system) with masses roughly between 0.5 - 10 Earth masses. These
planets need to be found at distances from their parent star such
that the planet's temperature and atmospheric pressure are supportive
of the existence of liquid water.
Direct methods for examining stars in our nearby neighborhood for the
existence of planets would involve the detection of starlight
reflected by an orbiting planet or perhaps by the emitted thermal
radiation from the planet itself. Optical reflected light and
infrared thermal radiation could both be analyzed spectroscopically
(provided astronomers could actually detect this gentle signal amid
the powerful fury of its host star) to present information about the
size, sunlight reflectivity (albedo) and temperature of a planet.
Indirect methods of planetary detection include measurements of
radial velocities of nearby stars, measurements of pulsar rates,
actual changes in the position of a host star based on gravitational
pull of planets or changes in the apparent brightness of the host
star due to transits and microlensing events. Each of these methods
can indicate the presence of external bodies around nearby stars.
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