*THE SOUTHWORTH PLANETARIUM*
*207-780-4249 <207-780-4249> www.usm.maine.edu/planet
<http://www.usm.maine.edu/planet> 70 Falmouth Street Portland, Maine 04103
43.6667° N, 70.2667° W Founded January 1970*
* "We'll leave the night on for you."*
*THE DAILY ASTRONOMER*
*Tuesday, April 19, 2016*
*Outrunning the Night and Other Ideas*
*--------------------------------------------------*
*STAR DOME ASTRONOMY!*
*Our introductory astronomy class begins tonight.*
*Walk in registrations welcome.*
*Class begins at 7:00 p.m. *
*Doors open at 6:15 p.m,*
*Enrollment: $70.00 ($50.00 for members)*
*For more information, consult our web-site:
http://usm.maine.edu/planet/star-dome-astronomy-level-i
<http://usm.maine.edu/planet/star-dome-astronomy-level-i> )*
*--------------------------------------------------------*
*This week, we are bound, gagged and determined to sort through the pile of
parchments now packed in Pandora's Pouch. Well, it's actually a jar, but
using that word would have messed up the alliteration. Each piece of
parchment contains an astronomical question that someone sent to us. We
store these questions to be answered at a later date. We generally
devote one day a week to addressing these queries. However, during this
rather busy week, we decided to answer questions each day this week, apart
from Friday, which, of course, is quiz day. *
*Please continue sending questions! *
*For an archive of past questions and answers, consult our "Ask the Staff
Astronomer" web-site: http://usm.maine.edu/planet/ask-staff-astronomer
<http://usm.maine.edu/planet/ask-staff-astronomer>*
*"I remember reading a science fiction story about Moon colonists who were
able to out run the night. The night-line moved across the lunar surface
more slowly that they were running, so by running, they could remain in
daylight. Is the science behind this idea right?" Martha P, Michigan.*
*Well, this is a very interesting idea: outrunning the night-line. The
answer is a bit involved, so we will address this one in stages.*
*First, the lunar line of demarcation separating daylight and night is
called the terminator. As the moon rotates on its axis, this line
advances across its surface, just as as Earth's "terminator" constantly
advances around the planet. Earth, however, possesses an atmosphere,
which refracts the sunlight, causing the twilight phases which follow
sunset and precede sunrise. The moon lacks an atmosphere, so its
terminator is sharply defined. *
*Determining how fast this terminator moves requires some math, but we'll
be gentle.*
*First, the moon's rotates once on its axis every 29.5 Earth days.*
*The moon's equatorial circumference (the distance around the moon's
equator) is about 10920 km (6770 miles). Now, 29.5 days equals 708
hours. So, at the lunar equator, the terminator advances at 15.4
kilometers (9.5 miles) per hour. *
*Running that quickly requires some stamina. The world record for a
marathon completion time is 2:02:57 by Dennis Kimett. (Surprise! He's from
Kenya). To run a marathon that quickly, Dennis had to run an average
speed of 12.9 miles per hour. So, runners who are as fast as Dennis
Kimett and other fast marathon runners could outrun the lunar terminator on
the equator. *
*Realize, that the 99.99999999999% of Earth's runners who are slower could
outrun the terminator at higher latitudes. Points on the moon at
increasing distance from the equator move at reduced speeds. For
instance, at latitude 45 degrees N or S on the Moon, the terminator is
moving at 6.7 miles per hour. At 66.5 degrees N or S, the terminator speed
is about 3.8 miles per hour. A rapid walker could outpace the lunar
terminator at its higher latitudes.**
*"I am already hearing about the total solar eclipse that America will
experience in August 2017. Will the solar eclipse be total in Maine?"*
*-No, unfortunately.*
*We will see the Sun partially eclipsed in August 2017. Here, we'll see
about 65% of the Sun blocked by the moon during this eclipse. Mainers will
next see a total solar eclipse in 2024. *
*"The Mercurian Transit module mentioned that Venus and Mercury would
transit the Sun simultaneously sometime in the very distant future. I
wondered, can a transit of Mercury and transit of Venus happen in the same
year? Or, can a single year have two Mercurian transits or two Venusian
transits?" -S.F., South Portland.*
*Yes, transit of Mercury and transits of Venus can happen in the same year,
but such years are rare. The last year this happened was 1769. The next
time we'll have two transits will be 2611. No single year can ever have
two transit of Mercury or two transits of Venus. *
**To calculate the terminator's speed, multiply the equatorial speed (9.5
mph) by the cosine of the latitude. To see an example of this calculation
for Earth, consult the planetarium's "Math Zone" web-page:
http://usm.maine.edu/planet/mz4-determining-speed-earths-rotation-given-latitude
<http://usm.maine.edu/planet/mz4-determining-speed-earths-rotation-given-latitude>
''*
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