Nope....it's like a big nuclear explosion being held together by it's own gravity. But instead of splitting atoms like in nuclear weapons it is fusing them together to make heavier elements. The sun is about 75% hydrogen and about 24% helium with 1% of its mass comprising other gases. Four hydrogen atoms fuse together under intense heat and pressure to create 1 helium atom. Even if the core was a solid surface such as iron...then the nuclear fusion would stop and the sun would contract in to an extremely dense ball of gas. But the sun will never have a core of iron. The suns life will end after it fuses helium in to carbon and oxygen during it's red giant stage. Then at this point the sun will contract to the size of the earth and become a white-dwarf. Radiating away intense heat but undergoing no fusion. Scientists know what matter makes up the sun with the use of a spectrometer. Basically what a spectrometer does is measures the wavelengths of light from the sun. And from this information we can tell precisely what the composition of the sun is made of. We can do this with stars and galaxies billions of light years away. I hope you find this useful.

It has a smooth nonsolid but well defined surface.

That's a great question - given that we hear about the temp of the sun's surface and all. It has arbitrary layers defined by us. They are handy for studying and describing the sun. But no, even if you could handle the heat and gravity you wouldn't be able to find a place to stand.

No. It has no surface.

1) "The photosphere is the visible surface of the Sun that we are most familiar with. Since the Sun is a ball of gas, this is not a solid surface but is actually a layer about 100 km thick (very, very, thin compared to the 700,000 km radius of the Sun). When we look at the center of the disk of the Sun we look straight in and see somewhat hotter and brighter regions. When we look at the limb, or edge, of the solar disk we see light that has taken a slanting path through this layer and we only see through the upper, cooler and dimmer regions. This explains the "limb darkening" that appears as a darkening of the solar disk near the limb." "Since the Sun is a ball of gas it does not have to rotate rigidly like the solid planets and moons do. In fact, the Sun's equatorial regions rotate faster (taking about 24 days) than the polar regions (which rotate once in more than 30 days). The source of this "differential rotation" is an area of current research in solar astronomy." Source and further information: http://solarscience.msfc.nasa.gov/surface.shtml 2) "we can see a CONSISTENT set of surface features in these images that MOVE from left to right as the sun rotates. These features are completely consistent and move UNIFORMLY across the surface. In other words, they do not move at different rates near the equator than than they move at the poles like the photosphere. Whatever this "structure" is, it absolutely cannot be the photosphere or the chromosphere because of it's consistency. This photographic evidence stands in direct opposition to present theories of the sun which claim that the sun is a giant ball of gas and has no solid surface below the photosphere. If Galileo assumed that the sun was not solid simply because it's OUTER "surface" layer (really just a liquid-like photosphere) did not move uniformly, then this uniformity of movement and rigidly defined surface definition turns the tables 180 degrees! The foundational pillar of the gas model theory is laid to waste in these uniformly moving images. We now need a new model of the sun. The old one doesn't work." Source and further information: http://www.thesurfaceofthesun.com/running.htm 3) "I recently found an website named thesurfaceofthesun.com and they contend that the surface of the sun is solid iron, did something change? My understanding was that iron was the last element to degrade before stars blew up. I always understood that all of the other elements would be gone leaving only iron at the end of a star. You are not misinformed. The commonly accepted paradigm for the the make-up of the Sun has stayed the same, and there is a lot of evidence to back it up. There are a few people who believe that the Sun is made of iron, and believe that they have found strong evidence to support this. As we have stated in other places, we do not feel that the "Curious" site is not the appropriate place to debate the indepth details of such models, although I should note that it takes only basic Physics to find flaws in the idea of a solid iron surface to the Sun (for example the fact that iron is vapourized at the temperature of the Sun's surface). If you do want more details I would like to refer you to the Bad Astronomy and Universe Today Forum which hosted this thread in June-July 2005 in which the author of thesurfaceofthesun.com debates his model with various other members of the forum. The gaseous sun model, rather than being outdated as the website you refer to suggests, is backed up by several lines of very recent evidence." Source and further information: http://curious.astro.cornell.edu/question.php?number=673

Scientists *do NOT* know what matter makes up the sun with the use of a spectrometer. That technique *assumes* that the sun is not mass separated to any significant degree. The sun's atmosphere is composed of mass separated layers of plasma with hydrogen and helium making up the two outermost layers of the sun. The sun's outer layers are hotter than it's inner layers because the atmosphere is electrically active. This heat in the outer layers causes the hydrogen and helium layers to emit more photons and therefore astronomers erroneously assume that the sun is mostly made of hydrogen and helium. In reality it is composed of the same elements that make up Mercury, Venus, Earth and Mars, it's three closest physical neighbors. Much of the energy that comes from the sun is *NOT* internally generated, but rather the sun electrically interacts with the heliosphere, which is why solar wind particles are continuously being accelerated from the sun. The multimillion degree loops in the solar atmosphere are caused by massive electrical discharges in it's atmosphere. FYI SOHO "running difference" images, along with Doppler images show 'rigid features" that exist underneath the photosphere.