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Our Nearest Star:
Sol - The Sun The Sun : Sol's Surface : Sol's Core : Solar Eclipse : Solar Wind : Heliosphere Our Sun is a normal main-sequence G2 star, one of more than 100 billion stars in our galaxy, and is a yellow dwarf star, at the center of the Solar System.
The Sun (Sol by name) is by far the largest object in the solar system. It contains more than 99.8% of the total mass of the Solar System (Jupiter contains most of the rest).
It is often said that the Sun is an "ordinary" star. That's true in the
sense that there are many others similar to it. But there are many more
smaller stars than larger ones; the Sun is in the top 10% by mass. The
median size of stars in our galaxy is probably less than half the mass
of the Sun.
The Sun is about 4.5 billion years old. Since its birth it has used up
about half of the hydrogen in its core. It will continue to radiate
"peacefully" for another 5 billion years or so (although its luminosity
will approximately double in that time). But eventually it will run out
of hydrogen fuel. It will then be forced into radical changes which,
though commonplace by stellar standards, will result in the total
destruction of the Earth (and probably the creation of a planetary
nebula). The Sun orbits the center of the Milky Way galaxy at a distance of approximately 24,000 to 26,000 light years from the galactic center, moving generally in the direction of Cygnus and completing one revolution in about 225250 million years (one Galactic year). Its orbital speed was thought to be 220±20 km/s, but a new estimate gives 251 km/s. This is equivalent to about one light-year every 1,190 years, and about one AU every 7 days. These measurements of galactic distance and speed are as accurate as can be, given current knowledge, but this may change as more is learned. Since our galaxy is moving with respect to the cosmic microwave background radiation (CMB) in the direction of Hydra with a speed of 550 km/s, the sun's resultant velocity with respect to the CMB is about 370 km/s in the direction of Crater or Leo. Sol's Surface
The surface of the Sun, called the photosphere, is at a temperature of
about 5800 K. Sunspots are "cool" regions, only 3800 K (they look dark
only by comparison with the surrounding regions). Sunspots can be very
large, as much as 50,000 km in diameter. Sunspots are caused by
complicated and not very well understood interactions with the Sun's
magnetic field.
Sol's Core
The Sun's power (about 386 billion billion Mega Watts) is produced by nuclear fusion reactions. Each second about 700,000,000 tons of hydrogen are converted to about 695,000,000 tons of helium and 5,000,000 tons (=3.86e33 ergs) of energy in the form of gamma rays. As it travels out toward the surface, the energy is continuously absorbed and re-emitted at lower and lower temperatures so that by the time it reaches the surface, it is primarily visible light. For the last 20% of the way to the surface the energy is carried more by convection than by radiation.
When observing
the Sun with appropriate filtration, the most immediately visible
features are usually its sunspots, which are well-defined surface areas
that appear darker than their surroundings because of lower
temperatures. Sunspots are regions of intense magnetic activity where
convection is inhibited by strong magnetic fields, reducing energy
transport from the hot interior to the surface. 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
largest sunspots can be tens of thousands of kilometers across. The Sun's output is not entirely constant. Nor is the amount of sunspot
activity. There was a period of very low sunspot activity in the latter
half of the 17th century called the Maunder Minimum. It coincides with
an abnormally cold period in northern Europe sometimes known as the
Little Ice Age. Since the formation of the solar system the Sun's output
has increased by about 40%. In addition to heat and light, the Sun also emits a low density stream
of charged particles (mostly electrons and protons) known as the solar
wind which propagates throughout the solar system at about 450 km/sec.
The solar wind and the much higher energy particles ejected by solar
flares can have dramatic effects on the Earth ranging from power line
surges to radio interference to the beautiful aurora borealis.
The solar wind has large effects on the tails of comets and even has measurable effects on the trajectories of spacecraft.
Spectacular loops and prominences are
often visible. The Sun's magnetic field is very strong (by terrestrial standards) and very complicated. Its magnetosphere (also known as the Heliosphere) extends well beyond Pluto.
This still shows the locations of Voyagers 1 and 2. Voyager 1 is traveling a lot and has crossed into the Heliosheath, the region where interstellar gas and solar wind start to mix.
Starting with a view of our Milky Way galaxy, the orange gas in the animation above represents the interstellar medium. The bow shock is created because the Heliosphere is moving through like a boat through the water, crashing through the interstellar gases. The bow shock in front of the moving Heliosphere is similar to the one observed by the Hubble Space Telescope.
We don't know the exact location of the termination shock and changes in the solar wind cause it to expand, contract, and ripple like a plate underwater. Water spreads out over the plate in a relatively smooth flow but has a rough edge where the water slows down abruptly and piles up. The edge is like the termination shock, and as the water flow changes, the shape and size of the rough edge change.
for more information about Sol - Our Sun - visit Wikipedia » |
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