Asteroids were first observed with telescopes in the early 1800s, and in 1802, the astronomer William Herschel first used the word "asteroid," which means "starlike" in Greek, to describe these celestial bodies. Most of what we have learned about them in the past 200 years has been derived from telescopic observations.

Now, you can see some of our smaller neighbors up close and personal. Check out our Asteroids Pictures Gallery.

Image Credit: NASA, Jet Propulsion Laboratory

Scientists using NASA’s RHESSI spacecraft have measured the roundness of the sun with unprecedented precision. They find that it is not a perfect sphere. During years of high solar activity the sun develops a thin “cantaloupe skin” that significantly increases its apparent oblateness: the sun’s equatorial radius becomes slightly larger than its polar radius. Their results appear the Oct. 2nd edition of Science Express.

“The sun is the biggest and therefore smoothest object in the solar system, perfect at the 0.001% level because of its extremely strong gravity,” says study co-author Hugh Hudson of UC Berkeley. “Measuring its exact shape is no easy task.”

The team accomplished the task by analyzing data from the Reuven Ramaty High-Energy Solar Spectroscopic Imager, RHESSI for short, an x-ray/gamma-ray space telescope launched in 2002 on a mission to study solar flares. Although RHESSI was never intended to measure the roundness of the sun, it has turned out ideal for the purpose. RHESSI observes the solar disk through a narrow slit and spins at 15 rpm. The spacecraft’s rapid rotation and high data sampling rate (necessary to catch fast solar flares) make it possible for investigators to trace the shape of the sun with systematic errors much less than any previous study. Their technique is particularly sensitive to small differences in polar vs. equatorial radius or “oblateness.”

“We have found that the surface of the sun has rough structure: bright ridges arranged in a network pattern, as on the surface of a cantaloupe but much more subtle,” describes Hudson. During active phases of the solar cycle, these ridges emerge around the sun’s equator, brightening and fattening the “stellar waist.” At the time of RHESSI’s measurements in 2004, ridges increased the sun’s apparent equatorial radius by an angle of 10.77 +- 0.44 milli-arcseconds, or about the same as the width of a human hair viewed one mile away.

Diagram showing the sun's oblateness has been magnified 10,000 times In this diagram, the sun's oblateness has been magnified 10,000 times for easy visibility. The blue curve traces the sun's shape averaged over a three month period. The black asterisked curve traces a shorter 10-day average. The "wiggles" in the 10-day curve are real, caused by strong magnetic ridges in the vicinity of sunspots. Credit: NASA Goddard Space Flight Center > Larger image “That may sound like a very small angle, but it is in fact significant,” says Alexei Pevtsov, RHESSI Program Scientist at NASA Headquarters. Tiny departures from perfect roundness can, for example, affect the sun’s gravitational pull on Mercury and skew tests of Einstein’s theory of relativity that depend on careful measurements of the inner planet’s orbit. Small bulges are also telltale signs of hidden motions inside the sun. For instance, if the sun had a rapidly rotating core left over from early stages of star formation, and if that core were tilted with respect to its outer layers, the result would be surface bulging. “RHESSI’s precision measurements place severe constraints on any such models.”

The “cantaloupe ridges” are magnetic in nature. They outline giant, bubbling convection cells on the surface of the sun called “supergranules.” Supergranules are like bubbles in a pot of boiling water amplified to the scale of a star; on the sun they measure some 30,000 km across (twice as wide as Earth) and are made of seething hot magnetized plasma. Magnetic fields at the center of these bubbles are swept out to the edge where they form ridges of magnetism. The ridges are most prominent during years around Solar Max when the sun’s inner dynamo “revs up” to produce the strongest magnetic fields. Solar physicists have known about supergranules and the magnetic network they produce for many years, but only now has RHESSI revealed their unexpected connection to the sun’s oblateness.

“When we subtract the effect of the magnetic network, we get a ‘true’ measure of the sun’s shape resulting from gravitational forces and motions alone,” says Hudson. “The corrected oblateness of the non-magnetic sun is 8.01 +- 0.14 milli arcseconds, near the value expected from simple rotation.”

Further analysis of RHESSI oblateness data may help researchers detect a long-sought type of seismic wave echoing through the interior of the sun: the gravitational oscillation or “g-mode.” Detecting g-modes would open a new frontier in solar physics—the study of the sun’s internal core.

Image Credit: Gary Palmer

Three Chinese astronauts landed safely in China's central Inner Mongolia region on Sunday, after conducting the country's first spacewalk on Saturday. They returned to Earth in a Shenzhou-7 module after completing a 68-hour mission which Premier Wen Jiabao called a "great leap forward" for Chinese space technology.

Astronauts Zhai Zhigang, Liu Boming, and Jing Haipeng were examined by doctors and adapted themselves to Earth's gravity before exiting the module. They were then taken to a hospital for observation before returning to Beijing yesterday.

The three men launched at 9:10 PM on Thursday for China's third manned spaceflight. China had sent a lone Yang Liwei in space in 2003, and sent two men on a five-day journey in 2005. This successful spacewalk mission makes China the third to perform an extra-vehicular activity (EVA) after the United States and Russia.

Other tasks during the three day mission included performing trials on satellite data relay and releasing of a 40-kg companion satellite, which was left in the space with the orbital module and the extravehicular space suits.

Next, China has plans to construct a "simple" space laboratory by 2011 followed within nine years with a manned station. This is expected to coincide with plans for a future Chinese moon landing in the same timeframe as planned US moon landings.

Image Credit: China Photos/Getty Images
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During a news conference on Monday, NASA told reporters that it is delaying its mission to the Hubble Space Telescope until next year because of a serious breakdown of the observatory in orbit.

The malfunctioning system is Hubble's Control Unit/Science Data Formatter - Side A. Shortly after 8 p.m. on Saturday, Sept. 27, the telescope's spacecraft computer issued commands to safe the payload computer and science instruments when errors were detected within the Science Data Formatter. An attempt to reset the formatter and obtain a dump of the payload computer’s memory was unsuccessful.

Additional testing demonstrates Side A no longer supports the transfer of science data to the ground. A transition to the redundant Side B should restore full functionality to the science instruments and operations.

The transition to Side B operations is complex. It requires that five other modules used in managing data also be switched to their B-side systems. The B-sides of these modules last were activated during ground tests in the late 1980’s and/or early 1990, prior to launch. The Hubble operations team has begun work on the Side B transition and believes it will be ready to reconfigure Hubble later this week. The transition will happen after the team completes a readiness review.

Hubble could return to science operations in the immediate future if the reconfiguration is successful. Even so, the agency is investigating the possibility of flying a back-up replacement system, which could be installed during the servicing mission.

However, it would take time to test the replacement part and the astronauts have been training for a different type of servicing. They need time to train on the installation of the new part. NASA spokesman Michael Curie said NASA will also have to work out new mission details for the astronauts who have trained for two years to carry out five Hubble repair spacewalks.

For now, the October 14 launch has been postponed until at least early next year, possibly February.

Image Credit: NASA