BONUS: NEW MERCURY BUILDING THE NEXT- Mars: GUIDE TO OBSERVING GLOBALG MAP p. 39 GEN SUPERSCOPE p. 24 THE RED PLANET p. 50 & 54 THE ESSENTIAL GUIDE TO ASTRONOMY
Stellar Blackout over New York p. 30 See Quasars from Your Backyard p. 34
MARCH 2014 Planet Hunting Goes Public No scope, no sky, no problem! p. 18 Radically Different Telescope Mount p. 60 How the Web Saved the Webb p. 82
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FC Mar2014.indd 1 12/23/13 11:51 AM Mercury Earth Meet the planet nearest our Sun
Solid inner core The innermost planet has challenged astronomers for centuries. Its proximity to the Sun limits ground- Liquid Mercury outer core based telescopic observations, and when NASA’s Mariner 10 spacecraft made three close passes Mantle during the 1970s, the little planet appeared to have a Crust landscape that strongly resembled the Moon’s. But Mercury is no Moon. NASA’s Messenger spacecraft, in orbit around the Iron Planet since Solid inner core March 2011, has recently fi nished its initial global Moon survey. The work reveals that this wacky world has Liquid outer core a unique, complex history all its own. Mantle The survey images show a marvelous world of Solid ancient volcanic fl oods and mysteriously dark ter- inner core Crust rain (S&T: April 2012, page 26). Plains — mostly Liquid volcanic — cover about 30% of the surface. And outer core as radar images have long suggested, subsurface Mantle water ice lies tucked inside some polar craters. Crust Temperatures in the coldest craters never top 50° above absolute zero, making Mercury both one of the hottest and coldest bodies in the solar system. To celebrate Messenger’s completed Mercury survey, we’ve worked with the USGS to produce a labeled map of the innermost planet, which you’ll fi nd on the fl ip side of these pages. The labels on this map are a subset of those that appear on our new Mercury globe. Many names honor artists, writers, and musicians, including Bach and Cop- land. Even Disney and Seuss have craters.
Prokofi ev Crater’s north-facing rim and interior remain in perpetual shadow, making it a safe haven for water ice. Watch an animation of how illumina- tion changes over the course of one Mercury day at
skypub.com/prokofi ev. NASA GSFC / MIT JHU APL CIW
39
Gatefold March2014.indd 39 12/24/13 11:46 AM Mercury’s Strange Orbital Dance
Day 176 Day 2 orbits Day Mercury 0 3 rotations 132 0.47 a.u. 0.31 a.u. Sun Day Day 88 44 1 orbit 1½ rotations
Perihelion precesses 2° per century
The perihelion of Mercury’s orbit precesses 2° per century. Astronomers could explain all but Mercury rotates three times for every two orbits around the Sun. This 43″ of that shift with classical mechanics; they 3:2 spin-orbit resonance means that for a hypothetical astronaut on the needed Einstein’s theory of gravity to explain surface (black dot), sunrise comes only once every 176 Earth days. At the rest. The orbit’s elongation and advance perihelion, dayside temperatures reach about 700 K; at aphelion, 500 K. are highly exaggerated to emphasize the eff ect.
S&T Illustrations: Gregg Dinderman Globe map: USGS / NASA / JHU APL / CIW
This Messenger image shows mysterious “low- refl ectance material” excavated by craters near the eastern edge of Caloris Basin. The reddish deposits appear to be volcanic in origin. The orbiter took this composite image using all 11
NASA / JHU APL CIW color fi lters of its wide-angle camera.
Gatefold March2014.indd 40 12/23/13 12:03 PM
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