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Mercury magazine

Summer 2011 - Volume 40, Number 3

Summer 2011 - Volume 40, Number 3

Table of Contents



[14] The 2012 Transit of Venus, Paul Deans
Only six Venus transits have ever been observed; the one in 2012 will be the 7th. Discover a little transit history and learn how to safely observe this upcoming historical event.

[22] A Clever Way to Measure Distances to Galaxies, Joseph B. Jensen
Astronomers have developed a technique that measures the average brightness of thousands of red giant stars in a far-off galaxy to determine its distance.

[27] STEM at the College and University Level, Michael G. Gibbs
Once students are inspired toward STEM in elementary, middle, or high school, what is being done to support this interest when they reach college or university?

[31] Astronomy in the News
Surprises at Mercury, a Saturnian moon hiding salt, and a gravitational lens reveals an early spiral galaxy — these are some of the discoveries that recently made news in the astronomical community.


[4] Editorial, Paul Deans
Write On

[5] First Word, James G. Manning
A Walk in the Woods

[7] Echoes of the Past, Katherine Bracher
90 Years Ago: Photographing the Planets

[8] Annals of Astronomy, Clifford J. Cunningham
Erasmus Reinhold at 500

[9] Astronomer's Notebook, Jennifer Birriel
Origin of Interstellar Absorption Features

[10] Planetary Perspectives, Daniel D. Durda
Curious Corrugations in Saturn's C Ring

[11] Armchair Astrophysics, Christopher Wanjek
The Death of Astrophysics?

[12] Education Matters, David Bruning
Opening the Door to Conceptual Understanding

[13] Reaching Out, Bethany Cobb
Public Audiences Are Different

[36] Society Scope/ASP Supporters
ASP Award Winners

[40] Sky Sights, Paul Deans
In Search of the Milky Way

[43] Reflections, Nick Risinger
Photoptic Sky Survey

The 2012 Transit of Venus

by Paul Deans

Two astronomers observed it in 1639. Hundreds viewed it in 1769. Hundreds of thousands of spectators caught at least a glimpse of it in 1882. No one knows how many millions -- perhaps even hundreds of millions -- witnessed it in 2004. And June 5/6, 2012, is your only opportunity to see it. So, where will you be during next year's transit of Venus?

The phrase "once in a lifetime" denotes a rare event. A Venus transit is actually a twice-in-a-lifetime event, because two transits occur within a span of eight years. But each transit pair is separated from the next (and previous) pair by more than a century. Since the invention of the telescope, only three transit sets have occurred: 1631 and 1639; 1761 and 1769; and 1874 and 1882. The current pair (2004 and 2012) concludes next year. Miss 2012, and you'll have to wait 105 years -- until December 11, 2117 -- for the start of the next transit pair (2117 and 2125).

Why so rare? It's all in the tilt.

A Clever Way to Measure Distances to Galaxies

by Joseph B. Jensen

In 1998, competing teams of astronomers were forced to come to grips with increasingly convincing observations that the expansion of the universe was accelerating, rather than decelerating (as they expected). This cosmic acceleration provided the first clear evidence that a completely unknown force, called "dark energy," dominated the total mass and energy of the universe. The nature of dark energy is one of the most important and compelling questions in all of science today. Its discovery resulted directly from measurements of the distances to remote galaxies.

Determining how far away galaxies are is crucial to our understanding of the universe. Only when we accurately establish the distance to a remote object can we understand many of its properties, particularly what source of energy powers its luminosity. Distance measurements tell us how big the universe is, how old it is, how it changes with time, and what its eventual fate will be. For many years, systematic errors in those measurements led to the awkward conclusion that the universe is younger than the oldest stars in it — a conflict that had astronomers stumped until the 1998 discovery of cosmic acceleration.

STEM at the College and University Level

by Michael G. Gibbs

When thinking about those who provide astronomy and space science Education and Public Outreach (EPO) programs, which groups do you immediately think of? Perhaps amateur astronomers interacting with the public at star parties comes to mind. Or you might consider programs in our K–12 schools — such as the Astronomical Society of the Pacific's "Project ASTRO," which works with in-service teachers in middle and high schools. Others might think about science centers and planetariums across the country that offer special programs for K–12 students. These are but a few examples.

Often we think of EPO programs, primarily in the K–12 range, that engage our children and students in science, and use astronomy as a spark to generate interest in science, technology, engineering, or mathematics — the STEM fields. But once students are inspired in elementary, middle, or high school, what is being done to support them when they reach college or university? What's being done to sustain the interest of undergraduate and graduate students to give them the needed STEM education before they enter the workforce?

Astronomy in the News
Evidence Indicates Icy Saturn Moon Hiding Salt

University of Colorado at Boulder

Samples of icy spray shooting from Saturn's moon Enceladus collected during Cassini spacecraft flybys show the strongest evidence yet for the existence of a large-scale, subterranean saltwater ocean. The new discovery was made during the Cassini-Huygens mission to Saturn, a collaboration of NASA, ESA, and the Italian Space Agency. The plumes shooting water vapor and tiny grains of ice into space were originally discovered emanating from Enceladus by the Cassini spacecraft in 2005. The plumes were originating from the so-called "tiger stripe" surface fractures at the moon's south pole and apparently have created the material for the faint E Ring that traces the orbit of Enceladus around Saturn.

During three of Cassini's passes through the plume, the Cosmic Dust Analyser, or CDA, on board measured the composition of freshly ejected plume grains. The icy particles hit the detector's target at speeds of up to 11 miles per second, instantly vaporizing them. The CDA separated the constituents of the resulting vapor clouds, allowing scientists to analyze them.

The study shows the ice grains found further out from Enceladus are relatively small and mostly ice-poor, closely matching the composition of the E Ring. Closer to the moon, however, the Cassini observations indicate that relatively large, salt-rich grains dominate.

"There currently is no plausible way to produce a steady outflow of salt-rich grains from solid ice across all the tiger stripes other than the salt water under Enceladus' icy surface," said Frank Postberg of the University of Germany.

"The study indicates that 'salt-poor' particles are being ejected from the underground ocean through cracks in the moon at a much higher speed than the larger, salt-rich particles," said CU-Boulder faculty member and study co-author Sascha Kempf of the Laboratory for Atmospheric and Space Physics.