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Mercury magazine

Winter 2009 - Volume 38, Number 1

Winter 2009 - Volume 38, Number 1

Table of Contents



[12] Dark Night, Rowena Davis
Around the world, the dark of night is vanishing. The International Dark-Sky Association is leading the movement to save our starry skies.

[18] Imaging the Universe Online, Paul Deans
The Internet contains so much stuff it should be called the UWW (Universe Wide Web), but you need to know where to look to uncover the best images of the cosmos.

[24] Time-Domain Astronomy, John Avant
The first 120 years of night-sky record keeping, a heritage that largely resides on photographic plates, is in danger of being lost.

[29] Astronomy in the News
Dating small craters on Mars, images of extra-solar planets, and an update on a 'cosmic ghost' -- these are some of the discoveries that have recently made news in the astronomical community.


[4] Editorial, Paul Deans
The View From Above

[5] First Word, James G. Manning

[6] Astronomer's Notebook, Jennifer Birriel
Night Sky Brightness

[7] Planetary Perspectives, Daniel D. Durda
Planetary Science in the Red

[8] Armchair Astrophysics, Christopher Wanjek
Tales From the Edge of the Universe

[9] Echoes of the Past, Katherine Bracher
50 Years Ago: Rotation in the Solar System

[10] Annals of Astronomy, Clifford J. Cunningham
How Long Is a Year?

[11] Education Matters, David Bruning
Thinking About Thinking

[35] Society Scope/ASP Supporters

[40] Sky Sights, Paul Deans
The Sky of February, March, and April

[43] Reflections, Paul Deans
Take the IYA Beyond 2009

Dark Night

by Rowena Davis

What do the reproductive habits of sea turtles have to do with the view of the constellation Cassiopeia? How can smart security practices help inner-city children locate Orion’s Belt in the sky? These threads are all tied to the concept of sensible lighting.

Such concerns can become the basis of a smart lighting plan that enhances safety and recreation while improving nighttime ambiance and revealing the tapestry of stars unobscured by light pollution. Without care, the myriad needs of a developed society can blanket the night with inappropriate illumination that robs citizens in cities around the globe of a vital natural resource.

For 20 years the International Dark-Sky Association (IDA) has made the task of protecting the night its sole mission.

Imaging the Universe Online

by Paul Deans

Whether it's in my role as Mercury editor or while I'm working on other projects, I spend numerous hours surfing the Web. Much of the time I'm looking for images -- night-sky scenes, planets, constellations, stars, nebulae, galaxies, or exotic cosmic doodads for which there are no photos, only artist's impressions.

While searching, I'm particularly conscious of copyright. The ASP has an excellent reputation, and we have never a problem securing permission to use photos in Mercury. But some sites are (justifiably) touchy about how their images are used, and while I like to always select the best I can find, there are times when a copyright-free (or public-domain) image is the best way to go. The public-domain route is often the easiest one for educators to follow, too. The image is there for the downloading: no muss, no fuss.

In this article I've tried to include sites that offer nothing but public-domain images and video clips, I've added a brief section on astronomical illustrations, and since Earth is an astronomical object, I've included websites containing striking images of our planet from space.

Time-Domain Astronomy

by John Avant

Mike Aubrey, a senior at West Henderson High School in North Carolina, was facing a problem not uncommon to young people involved in the study of science. Mike needed a topic for his senior physics paper, and he wanted to do something more than the traditional classroom or library-bound "answer in the back of the book" report. He wanted a real hands-on project; the opportunity to learn by doing.

Fortunately, Mike was able to find his opportunity at the Astronomical Photographic Data Archive (APDA), a collection of historic spectral photographic plates at the nearby Pisgah Astronomical Research Institute (PARI). Working with Dr. Michael Castelaz, PARI's research director, Mike selected 13 spectral plates of Mira (Omicron Ceti) that were recorded from 1914 to 1949. He scanned the images and correlated variations in the hydrogen emission lines with archival light curves from the American Association of Variable Star Observers.

From his observations, Mike was able to postulate that the hydrogen-line intensities change as Mira contracts and expands. In the process, Mike experienced an original research project and developed a passion for more.

Astronomy in the News
Dating Small Martian Features

Planetary Science Institute

The crater-counting system that scientists have used since the 1970s to determine the age of large geologic features on Mars will also allow them to date small features, such as riverbeds and lava flows, according to William K. Hartmann, a senior scientist at the Tucson-based Planetary Science Institute.

Crater counting relies on the density, or crowding, of craters to determine the age of planetary surfaces. It works on the assumption that older landforms have been exposed for longer periods and have been hit by more meteorites than younger surfaces.

While the method is widely recognized as valid for large, miles-wide craters, some scientists had questioned whether the rate at which small craters form is well enough understood and constant enough to be trusted in predicting the age of a landform.

The issue didn't arise until 1997, when the small craters first became visible in images returned by the Mars Global Surveyor high-resolution cameras. In recent years, many more high-resolution images have come from the HiRISE camera aboard Mars Reconnaissance Orbiter.

The crater-counting system, which Hartmann first proposed in the 1960s, was originally developed for counting large craters that are several miles wide.

"Using small craters to predict the age of landforms is complicated," Hartmann observed. While the large craters are formed by a single event, many small craters can be formed simultaneously when a large meteorite slams into the planet and throws debris into the air, which then falls as secondary meteorites, he explained.