Page 45 - Astronomy - October 2017 USA

about this, see “Stargazing in
ancient Egypt,” by Patricia
Blackwell Gary and Richard
Talcott, in the June 2006 issue
of Astronomy.
Michael E. Bakich
Senior Editor

Q: I OFTEN READ ABOUT A
SUNSPOT ON THE WESTERN
LIMB OF THE SUN, OR A
CRATER ON THE EASTERN
LIMB OF THE MOON, ETC.
AS THERE IS NO “UP” IN
SPACE, HOW ARE NORTH,
SOUTH, EAST, AND WEST
DETERMINED?
Tom Bennett
Bagley, Wisconsin

A: For more than 350 years, Vast clouds called dark nebulae, such as SAC SL 17 in the constellation Scorpius, are known to contain high concen-
cartographers drew lunar maps trations of dust that block out background starlight. You can find dust in every corner of the universe. FRED HERRMANN
showing the edge of the Moon
that was nearest the eastern of labeling directions on the among the stars of individual from such encounters.
horizon as the eastern limb. face of our daytime star. This galaxies (interstellar dust), and Another contribution, albeit
For north and south, they means that, for maps dated within our and other solar sys- minor, comes from comets.
adopted the traditional naked- post-1961, the Sun is the only tems (interplanetary dust). Two Cometary dust is probably the
eye orientation, with north up. solar system body on which a elements that arise from differ- most famous type in the inter-
In 1961, Commission 16 of “north up” map will have east ent types of stars form interga- planetary dust cloud. Most of it
the International Astronomical to the left. lactic and interstellar dust. lies dormant, frozen within the
Union determined that there Michael E. Bakich Dust made primarily of sil- icy nuclei of comets. When one
should be two types of lunar Senior Editor ica begins its life as particles of those objects nears the Sun,
maps: those intended for explo- condensing out of the atmo- however, the ice in the comet
ration (think astronauts) and spheres of cool red giant stars vaporizes and releases the dust
those intended for use at the Q: ASTRONOMY MAGAZINE that contain lots of oxygen. all along the comet’s orbit.
telescope. The first type labels HAS LOTS OF REFERENCES Carbon dust (which also Earth, in its yearly trip about
east in the same direction as TO DUST CLOUDS. WHAT IS includes carbon compounds the Sun, passes through dozens
Mare Crisium (Sea of Crises). “DUST” COMPOSED OF? such as silicon carbide) forms of these dust trails and the
As we gaze at the Moon when Dan Baum in similar red giant stars that result in each case is a meteor
it lies highest in the south, that Pendleton, Oregon are different in one way: Their shower.
feature lies near the right edge. atmospheres are rich in the Michael E. Bakich
So, for the past 57 years and on A: Three types of dust exist in element carbon. Another type Senior Editor
into the future, east is to the space, and none of them of intergalactic/interstellar dust
right, just as all terrestrial resembles what we call “dust” made of graphite comes almost
maps label it. on Earth. Here, outdoor dust exclusively from supernovae. Send us your
The second type, telescopic consists mainly of small par- Interplanetary dust contains questions
maps, show south up, as it ticles of soil and rock carried some of the dust that floats Send your astronomy
would be in a telescope that into the atmosphere by wind. between galaxies and stars, but questions via email to
inverts the image. This type of Indoor dust is a combination of it has some local components askastro@astronomy.com,
map doesn’t carry any “east” or soil attached to our shoes that as well. Asteroid and even or write to Ask Astro,
“west” directions. we carry in, human and animal planetary collisions early in the P. O. Box 1612, Waukesha,
The direction east is to the hair, tiny bits of paper and solar system’s history contrib- WI 53187. Be sure to tell us
right on maps of all other other fibers, pet dander, and a uted to what astronomers call your full name and where
objects in the solar system tiny percentage of human skin. the interplanetary dust cloud. you live. Unfortunately, we
except one: the Sun. For what- Astronomers find cosmic Researchers are currently try- cannot answer all questions
ever reason, astronomers have dust in the areas between gal- ing to figure out what percent- submitted.
never changed the convention axies (intergalactic dust), age of the local dust results

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