Sky and Telescope - September 2015 - 28

Last of the Four
CRATER TIMING GUIDE Craters and spots that stand out
well during a lunar eclipse are identiﬁed here. Approximate
times when the umbra's edge will cross them are listed at right.

Harpalus
Plato-
Pico-

-Aristoteles
-Eudoxus

Aristarchus
Timocharis -
Pytheas-

Proclus

Menelaus
Manilius

-Plinius

-Copernicus

Kepler-

Taruntius-
Dionysius-
-Grimaldi

Langrenus

Censorinus

Goclenius-

-Billy
-Birt
Campanus
-Tycho

R
: GA
S &T

America, its upper left side as seen from Europe.
The penumbra is the region where an astronaut
standing on the Moon would see Earth covering only
part of the Sun's face. The penumbral shading becomes
stronger as the Moon moves deeper in.
The second stage is partial eclipse. This begins much
more dramatically when the Moon's leading edge enters
the umbra: Earth's inner shadow where the Sun is completely hidden. With a telescope, you can watch the edge
of the umbra slowly engulﬁng one lunar feature after
another (see the Crater Timings box on the facing page),
as the entire sky begins to grow darker.
The partial phase will last just over an hour. As its

North
PENUMB

Total Eclipse of the Moon, Night of September 27-28, 2015
RA

Eclipse event
Partial
eclipse
ends
4:27 UT

Total
eclipse
ends
3:23 UT

UMBRA
Mideclipse
2:48 UT

Total
eclipse
begins
2:11 UT

Partial
eclipse
begins
1:07 UT

Moon enters
penumbra
0:12 UT
(unobservable)

Moo

West

East

Moon
leaves
penumbra
5:23 UT
(unobservable)

n's
path

South
S&T: LEAH TISCIONE

end approaches, only a ﬁnal bright sliver remains outside the umbra. By this time the rest should already be
showing a dim, foreboding reddish glow.
The third stage is total eclipse, beginning when the
last rim of the Moon slips into the umbra. But the
Moon won't black out: it's sure to glow some shade of
intense orange or red. This red light is sunlight that
has skimmed and bent through Earth's atmosphere, all
around the edge of our globe, on its way to the Moon. In
other words, it's light from all the sunrises and sunsets
that ring our world at any given moment. An astronaut
standing on the Moon would see the dark Earth thinly
rimmed with brilliant orange from the Sun hidden
behind it - brilliant enough to illuminate the lunar
landscape around him an eerie red.
This umbral light can change a lot from one eclipse
to the next. Two main factors aﬀect its brightness and
color. The ﬁrst is simply how deeply the Moon goes
into the umbra while passing through; the center of the
umbra is much darker than its edges. At mid-eclipse this
time, the Moon's south-southeastern edge will be only a
quarter of a lunar diameter inside the umbra, so expect
that side to be distinctly brighter than the rest.
The other factor is the state of Earth's atmosphere
along the sunrise-sunset line. If the air is very clear, the
eclipse is bright. But if a major volcanic eruption has
recently polluted the stratosphere with thin global haze,
a lunar eclipse will be dark red, ashen gray, or occasionally almost black.
In addition, blue light is refracted through Earth's
clear, ozone-tinted upper atmosphere above the thicker
layers that produce the red sunrise-sunset colors. This

September 2015 sky & telescope

EDT

CDT

MDT

PDT

Penumbra ﬁrst visible?

8:40 p.m.

7:40 p.m.

Partial eclipse begins

9:07 p.m.

8:07 p.m.

7:07 p.m.

Total eclipse begins

10:11 p.m.

9:11 p.m.

8:11 p.m.

7:11 p.m.

Mid-eclipse

10:48 p.m.

9:48 p.m.

8:48 p.m.

7:48 p.m.

Total eclipse ends

11:23 p.m.

10:23 p.m.

9:23 p.m.

8:23 p.m.

Partial eclipse ends

12:27 a.m.

11:27 p.m.

10:27 p.m.

9:27 p.m.

Penumbra last visible?

12:55 a.m.

11:55 p.m.

10:55 p.m.

9:55 p.m.

Sky and Telescope - September 2015

Table of Contents for the Digital Edition of Sky and Telescope - September 2015