Sky and Telescope - August 2017 - 49

be sure, look for "ISO 12312-2" printed
on them.
For binoculars or telescopes, you can
buy solar-ﬁlter material made of glass or
thin, metal-coated plastic ﬁlm - either
as a sheet you can cut with scissors to
attach over the front of your optics, or
pre-mounted in a cell sized to ﬁt ﬁrmly
onto the front (don't let it blow off!).
Leave the ﬁlm slack; wrinkles don't
matter, but stretching it will haze out
the view and compromise safety. When

oldest, simplest, but poorest projection method is to use a pinhole. For
instance, take a long box, cut a hole in
one end, tape aluminum foil over the
hole, and put a pinhole in the foil. Tape
white paper inside the other end of the
box, close it up, and cut a big hole in the
side so you can look at the paper. Aim
the pinhole at the Sun, and an image of
the Sun's face will fall on the paper.
But the image will be very small and
dim. Experiment with different sized

instrument at the Sun (without looking
in it! Move it around until its shadow
is minimized and light ﬂoods out of
the eyepiece). On a telescope, use your
lowest-power eyepiece. Focus the image
with the focus knob and/or by moving
the paper catching the image closer or
farther back. If the scope's aperture is
larger than about 3 inches, cut a clean,
3-inch hole in thin cardboard and tape
it over the front. You don't want to let a
damaging amount of solar heat inside.

The Christmas
2000 eclipse was
partial only. For
photographer
Fred Espenak,
its maximum
"eclipse magnitude" (middle
image) was 43%.

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What To Watch For

* Can you see any sunspots? Don't get
your hopes up; the Sun is well past the
2014 maximum of its 11-year activity
cycle, and its face these days is pretty
quiet, sometimes completely blank. But
if you do see a spot or two, they will
be landmarks for events coming up. If
you're projecting the Sun's image onto
paper, wiggle the paper to distinguish
sunspots from tiny paper ﬂaws.
* First contact is the moment when
the edge of the Moon ﬁrst touches
the Sun's western edge. Find the exact
time of this event for your location by
clicking on the Google Map at https://
is.gd/2017eclipsemap. But the Moon's
edge will take a little while after ﬁrst
contact to intrude enough to begin to
show. How well can you time when this
happens? What's the delay as seen with
your setup? Set your timepiece accurately beforehand.
* As the Moon leisurely intrudes farther onto the Sun, look for irregularities

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itud

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Pat
ag.
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2m
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0.8

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CD T

11:45

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18:1
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30s

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1:15
pm

2m

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2m

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10:30 a

10:15 am PDT

inut
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17:45 U
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17:30 UT

0.6

2m

MICHAEL ZEILER

pinholes. A large one makes the image
bright but fuzzy; a small one makes it
sharp but dim.
Much better is to use binoculars or a
telescope to project a big, bright image,
as shown on the next page. Aim the

3:0

17:15 UT

we tested various glass and thin-ﬁlm
solar ﬁlters few years back, we liked the
Baader Astro-Solar thin ﬁlm the best.
Projection means projecting an
image of the Sun onto a piece of white
paper and watching the paper. The

t Zooming in for more detail. Along the path of
totality, extremely narrow red ellipses tell the duration of total eclipse by time ticks at their ends.
s k y a n d t e l e s c o p e .c o m

* AUGUST 2017

49
http://www.is.gd/2017eclipsemap http://www.is.gd/2017eclipsemap http://www.skyandtelescope.com
Sky and Telescope - August 2017

Table of Contents for the Digital Edition of Sky and Telescope - August 2017
