Solar Prominence

A prominence is a feature of a layer of the Sun’s atmosphere called the chromosphere. Magnetic fields suspend loops of gas—prominences—above the main photosphere layer. These loops are actually cooler than the rest of the photosphere, but they still appear bright against the dark sky.

 

 

 

 

 

 

 

 

 

 

 

 

Interior of the Sun

Regions of the Sun include the core, radiation zone, convection zone, and photosphere. Gases in the core are about 150 times as dense as water and reach temperatures as high as 16 million degrees C (29 million degrees F). The Sun’s energy is produced in the core through nuclear fusion of hydrogen atoms into helium. In the radiation zone, heat flows outward through gases that are about as dense as water. The radiation zone is cooler than the core, about 2.5 million degrees C (4.5 million degrees F). In the convection zone, churning motions of the gases carry the Sun’s energy further outward. The convection zone is slightly cooler, about 2 million degrees C (3.6 million degrees F), and less dense, about one-tenth as dense as water. The photosphere is much cooler, about 5500° C (10,000° F) and much less dense, about one-millionth that of water. The turbulence of this region is visible from earth in the form of sunspots, solar flares, and small patches of gas called granules.

 

 

 

 

 

 

 

 

 

 

 

Star Trails

This long-exposure photograph shows the Delicate Arch, a rock formation in Utah, silhouetted against the trails of stars in the sky. The brightest and innermost trail, seen through the center of the arch, tracks the North Star. The North Star, also known as the polestar, is the star located closest to the north celestial pole of Earth’s axis. The apparent movement of the North Star and other stars through the night is caused by the rotation of Earth.

 

 

 

 

 

 

 

 

 

 

Stellar Parallax

As Earth moves around the Sun, distant stars appear to move in the sky. This apparent displacement, known as stellar parallax, is most evident at six-month intervals, when Earth is at opposite ends of its solar orbit. Astronomers use stellar parallax to determine a star’s distance from Earth by studying the angle formed by the actual star and its two parallactic positions (seen here as dotted blue lines). Astronomers can determine a star’s motion by comparing distance measurements over a period of time. This illustration depicts two examples of stellar parallax.

 

 

 

 

 

 

 

 

 

Fission and Fusion Processes

Nuclear energy can be released in two different ways: by fission (splitting) of a heavy nucleus, or by fusion (combining) of two light nuclei. In both cases energy is released because the products have a higher binding energy than the reactants. Fusion reactions are difficult to maintain because the nuclei repel each other, but unlike fission reactions, fusion does not create radioactive products. Stars produce their energy through nuclear fusion.

 

 

 

 

 

 

Life of a Star

A star begins life as a large, relatively cool mass of gas in a nebula, such as the Orion Nebula (left). As gravity causes the gas to contract, the nebula’s temperature rises, eventually becoming hot enough to trigger nuclear reactions in its atoms and form a star. A main sequence star (middle) shines because of the massive, fairly steady output of energy from the fusion of hydrogen nuclei to form helium. The main sequence phase of a medium-sized star is believed to last as long as 10 billion years. The Sun is just over halfway through this phase. Stars eventually use up their energy supply, ending their lives as white dwarfs, which are extremely small, dense globes, or in the case of larger stars, as spectacular explosions called supernovas. A supernova is shown within the Large Magellanic Cloud at the bottom right of the rightmost photo.

 

 

 

 

 

 

 

 

 

 

 

 

Stellar Nursery

Stars form in dense clouds of gas and dust such as this one, called the Rho Ophiuchi dark cloud. These clouds are so dense that visible light produced by the stars is blocked by the dust. Astronomers use infrared telescopes in space to detect emissions from new stars.

 

 

 

 

 

 

 

 

 

 

 

 

Dust Disk around Vega

Astronomers believe that a new star forms from a cloud of dust and gas and that a disk of dust and gas often remains around a star. Astronomers theorize that planets may eventually condense out of such disks. In 1983 astronomers discovered that the star Vega is surrounded by a disk of small particles, probably dust, rock, and ice. Vega was the first star other than the Sun known to be orbited by such a disk. This artist's rendering shows how Vega may look.