THE USM SOUTHWORTH PLANETARIUM
207-780-4249        www.usm.maine.edu/planet
70 Falmouth Street   Portland, Maine 04103
43.6667° N                   70.2667° W
Founded January 1970
Julian date:    2458058.5
2017-18:   # 30


THE DAILY ASTRONOMER
Wednesday, November 1, 2017
Beyond Neptune

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THE SOUTHERN MAINE ASTRONOMERS
MEETING ON THURSDAY IS CANCELLED.
As many members are still without power, the SMA
has decided to cancel its monthly meeting at the
Southworth Planetarium.  Our apologies for the
inconvenience.
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We will certainly meet our Pandora deadline this time.  We have two
months remaining to answer slightly more than thirty queries tucked
deep into Pandora's Jar.   We invite you to submit your own questions
to help us fulfill our promise!

PANDORA PARCHMENT #  66     "How is it that astronomers can see so
many distant galaxies, but are having such a difficult time observing
the planet they believe exists beyond Neptune?"  -S.H.  South Portland


Sometimes distance isn't as important as the light source.
Astronomers can observe distant stars and galaxies because they emit
their own light.    In the case of galaxies, the light output is so
intense that one can observe them even over many millions or billions
of light years, through telescopes, that is.
However, we only see planets because they reflect the light of their
parent stars.    A planet's brightness is determined by its distance
from the Sun and its distance from us.   The farther a planet is from
the Sun, the fainter the light it receives and, by extension, the
light it reflects.    The reflected light becomes more attenuated the
farther it travels.    We refer to this diminishment as the "Inverse
Square Law."      If you double your distance from a light source, the
light's intensity will be reduced to one fourth of its previous value.

Planet Nine is a planet that many astronomers believe must exist well
beyond Neptune.  According to estimates, its average distance might be
700 Astronomical Units, or 700 times farther from the Sun than Earth.
     It highly elongated orbit can bring it as far away as 1200
Astronomical Units, and as close as 200 Astronomical Units.    Even
when at its closest, Planet Nine (if it exists) will be 2.5 million
times dimmer than the faintest naked eye stars.    It is also believed
to be highly inclined relative to the ecliptic plane, the band where
we observe the planets.   Consequently, the search region is vast and
the object we're trying to find quite faint.

If Planet Nine does exist, it will be much closer to us than the stars
and galaxies, but it will still be much fainter and therefore harder
to find.