Exploring The Universe

A Solar Corona Ejection - November 8th, 1996.

"The Sun would not be a nice place to spend the summer. One reason, besides the extreme heat, is that explosions are common there. In the above picture, magnetic fields buckle, releasing previously constrained hot material from the upper atmosphere of the Sun. As a result, hot gas streams out into the Solar System, impacting planets, moons, spacecraft, and making space a dangerous place for astronauts. Known as coronal mass ejections (CMEs), billions of tons of scathing plasma can be accelerated to millions of miles per hour. CMEs are more common but less intense than solar flares."

The Equal Night - September 22nd, 1996.

"On September 22nd, 1996, the Sun crossed the celestial equator heading south - marking the Autumnal Equinox, the first day of Autumn. Equinox means equal night and with the Sun on the celestial equator, Earthlings will experience 12 hours of daylight and 12 hours of darkness. Then, for those in the northern hemisphere, the days will begin to grow shorter with the Sun marching lower in the sky as winter approaches. A few weeks after the Autumnal Equinox of 1994, the crew of the shuttle Endeavor recorded this image of the Sun poised above the Earth's limb. The glare illuminates Endeavor's vertical tail (pointing toward the Earth) along with radar equipment in the payload bay."

The Sun Erupts - September 16th, 1996.

"The Sun is a seething ball of extremely hot gas. Above, the Sun was captured by Skylab in 1973, throwing off one the largest eruptive prominences in recorded history. The Sun has survived for about 5 billion years, and will likely survive for 5 billion more. The Sun is not on fire, will never explode, and a solar flare will never destroy the Earth."

Driving to the Sun - July 27th, 1996.

"How long would it take to drive to the Sun? Brittany, age 7, and D.J., age 12, ponder this question over dinner one evening. James, also age 7, suggests taking a really fast racing car while Christopher, age 4, eagerly agrees. Jerry, a really old guy who is used to estimating driving time on family trips based on distance divided by speed, offers to do the numbers. "Let's see...the Sun is 93 million miles away. So, if we drove 93 miles per hour the trip would only take us 1 million hours." How long is 1 million hours? One year is 365 days, times 24 hours per day, or 8,760 hours. One hundred years would be 876,000 hours, still a little short of the 1 million hour drive time - so the Sun is really quite far away. Christopher is not impressed, but as he grows older he will be. You've got to be impressed by something that's 93 million miles away and still hurts your eyes when you look at it!"

The Iron Sun - May 21st, 1996.

"The ultraviolet light emitted by eleven times ionised iron at temperatures over 2 million degrees Farenheit was used to record the above picture of the Sun on May 16th, 1996. The image was made by the EIT camera onboard the SOHO spacecraft, a space observatory which can continuously observe the Sun. Eleven times ionised iron is atomic iron with eleven of its electrons stripped away. Here the electrons are stripped by the frantic collisions with other atoms and electrons, which occur at the extreme temperatures in the solar corona. Since electrons are negatively charged, the resulting ionised iron atom is highly positively charged. Astronomer's "shorthand" for eleven times ionised iron is written "Fe XII", the chemical symbol for iron followed by a Roman numeral 12 (Fe I is neutral iron)."

Helios Helium - May 20th, 1996.

"Above is an image of the relatively quiet Sun made on May 18th, 1996, in light emitted by ionised helium atoms in the Solar chromosphere. Helium was first discovered in the Sun in 1868, its name fittingly derived from the Greek word Helios, meaning Sun. Credit for the discovery goes to astronomer Joseph Lockyer. Lockyer relied on a developed technique of spectroscopy, dissecting sunlight into a spectrum, and the idea that each element produces a characteristic spectral pattern of bright lines. He noticed a yellow line in a solar spectrum made during an eclipse which could not be accounted for by elements known on Earth. Almost 27 years later, helium was finally discovered on Earth when the spectrum of a helium bearing mineral of uranium provided an exact match to the previously detected element of the Sun. Helium is now known to be the second most abundant element (after hydrogen) in the Universe."

The Sun 'Today' - May 18th, 1996.

"Our Sun shows a different face every day. The above picture was taken in red light on May 15th, 1996, and so is shown in red. The bright spots to the right of the center are active regions known as plages. At the time, the Sun was showing very few active regions or sunspots, and was considered to be in a solar minimum. Solar activity would pick up over the next six years, until a "solar maximum" was reached. The Sun goes through this cycle of maxima and minima every 11 years. Sol, our Sun, is hundreds of times more massive than all the planets in the Solar System combined. However, the Sun itself contains only a small amount of the total angular momentum of the Solar System."

The Sun Also Rises - November 17th, 1995.

"Sunrise seen from low Earth orbit by the shuttle astronauts can be very dramatic indeed. In this breathtaking view, the Sun is just visible peaking over towering anvil shaped storm clouds, whose silhouetted tops mark the upper boundary of the troposphere, the lowest layer of Earth's atmosphere. Sunlight filtering through suspended dust causes this dense layer of air to appear red. In contrast, the blue stripe marks the stratosphere, the tenuous upper atmosphere, which preferentially scatters blue light."

The Sun Spews X-Rays - October 4th, 1995.

"Our Sun is really very hot. The Sun's outer atmosphere is so hot that it emits much light in the X-ray band, which was unexpected. X-rays are usually emitted from objects having a temperature in the millions of degrees, not the mere thousands of degrees of the Sun's surface. The above X-ray picture shows the Sun one particularly active day in August of 1992. Evident are hot spots on the solar surface, showing that areas above the Sun's surface really do reach millions of degrees. But possibly more puzzling is the broader X-ray glow visible surrounding the Sun. This glow is now attributed to the Sun's X-ray corona, the origin of which is currently a subject of much discussion and debate. The Sun is one of the most photographed objects, with frequently updated pictures available over the WWW."

The Sun Erupts - August 13th, 1995.

"The Sun was captured in 1973 throwing one of the largest eruptive prominences ever recorded. Sol, our Sun, is a normal star. It formed about 5 billion years ago, and will last about another 5 billion years. The Sun will never explode, and a solar flare will never destroy the Earth. Eventually the Sun will become a white dwarf star. The Sun is made of mostly hydrogen and helium. The Sun's center is so hot that when hydrogen nuclei collide, they stick together and release energy - a process called nuclear fusion. No one knows why the center of the Sun emits so few neutrinos."