astronomy@iowa

One hundred thousand orbits, that is…

On August 11 the Hubble Space Telescope completed its 100,000th orbit of Earth since being placed in orbit by the space shuttle Discovery in 1990. In the last 18 years the telescope has logged over 2.7 billion miles (that’s over 5,700 trips to the Moon!) while speeding at 5 miles per second.

To Commemorate 18 years of astronomical service, the Space Telescope Science Institute (STScI) is giving away 18 prints of the star cluster NGC 2074 taken to commemorate the orbital milestone. Visit the official website hubblesite.org and submit a valid email address after clicking the “Learn more” link for a chance to be one of the lucky winners to receive a 16×20-inch print.

Hurry, the drawing ends August 18.

The annual Perseids meteor shower is underway and should peak within the next 24 to 48 hours. According to estimates, the best time to observe the shower will be in the early morning hours of Tuesday, August 12. Although meteors will be visible at any time after dark, prime conditions will occur after the Moon sets about 2 a.m.

For more information on observing the shower and its cause, check out my web page at www.brentstuder.com/kcc/perseids.html.

Everything seems to be “Go” for an October 5 launch of the Interstellar Boundary Explorer satellite. Problems with the Pegasus rocket that will lift the satellite from its perch under the belly of a modified Lockheed L-1011 jumbo jet appear to have been resolved and IBEX has been delivered to Vandenberg Air Force Base for several weeks of testing before being mated to the Pegasus launch vehicle. Eventually the assembled vehicle will be flown under the Orbital Sciences Corporation’s L-1011 to the pacific island of Kwajalein for the October launch. By using the facilities at Kwajalein atoll for the mission launch instead of Cape Canaveral or Vandenberg AFB, mission planners will be able to utilize the additional eastward rotational velocity near Earth’s equator to increase fuel load by a precious few pounds and thus increase the final orbit of the 175-pound IBEX. To obtain the best data, the spacecraft must fly as far out of Earth’s magnetosphere as possible.

The Sun and entire solar system are moving through a region of space referred to as the local interstellar medium, which is composed of material ejected by stellar winds, novae and supernovae. The boundary between the local interstellar medium and the Sun’s sphere of influence is just now being studied and of considerable interest to astronomers now that the Voyager 1 spacecraft reached the termination shock in December 2004 at a distance of 94 Astronomical Units from the Sun (1 A.U. is the average distance between the earth and Sun.) The termination shock is the boundary layer where the particles from the solar wind begin interacting with material from the interstellar medium causing the solar wind to abruptly slow from a supersonic flow to a subsonic flow. Beyond the termination shock as some unknown distance is the heliopause—the layer at which the pressure of the solar wind is balanced by the pressure of the interstellar medium hitting the solar wind—and beyond that is the bow shock, where the interstellar medium first encounters the Sun’s influence.

The sole scientific objective of the IBEX mission is to discover the interaction between the local interstellar medium and the solar wind by answering several questions: What is the strength and structure of the termination shock, how are energetic protons accelerated by the termination shock, what are the properties of the solar wind flow beyond the termination shock, and how does the interstellar flow interact with the solar wind beyond the heliopause? The IBEX spacecraft will do this by investigating energetic neutral atoms of hydrogen generated primarily in the region beyond the heliopause. Because neutral atoms are unaffected by the presence of electric or magnetic fields, the detectors on IBEX will be able to map the points of origin of the neutral atoms it observes.

For more information about the Interstellar Boundary Explorer mission check out the IBEX website or get more immediate updates on IBEX at Twitter.

Talk about a lucky strike! On the night of January 9, 2008, astronomers were using the Swift satellite to observe a supernova in the galaxy NGC 2770—90 million light-years distant in the constellation Lynx—when another one popped off in the same galaxy. A supernova such as SN 2007uy occurs when a massive star runs out of nuclear fuel in its core and the outward flow of energy is insufficient to balance the crushing inward force of gravity. In an instant, the star’s core catastrophically implodes triggering a shock wave that races outward through the star. Astronomers have long suspected that when the shock wave bursts through the star’s surface, a short x-ray burst would be produced. Because of the timing of such an event, astronomers have only seen the optical brightening of the exploding star, which lasts for many weeks, but have never seen the short x-ray brightening. Until now, that is.

On that day in January, astronomers Alicia Soderberg and Edo Berger were observing SN 2007uy in the distant spiral galaxy when they detected an x-ray brightening lasting five minutes that did not coincide with the observed location of the supernova. Because of the fortuitous observation and the design of Swift, the astronomers were able to make numerous measurements of the new supernova (designated SN 2008D) and test the theory of x-ray break-out as the shock wave rips the progenitor star apart. Happily the observations of Soderberg and 38 other astronomers confirm the theory after nearly 40 years.