Sky and Telescope - April 2015 - 51

Alan MacRobert

Learn how to use detailed star charts to ﬁnd the faintest things with your telescope: skypub.com/charts.

pens deep in the night and high in the
sky. For Australia, Japan, China, and
Southeast Asia, it comes on the evening
of April 4th local date.

Total Eclipse of the Moon, Morning of April 4, 2015
North

Moon's
path

JOHNNY HORNE

Take a fairly long exposure, and even a
partially eclipsed Moon shows the red-lit
land in the umbra of Earth's shadow.

Moon leaves
penumbra
15:01 UT
(unobservable)

Partial
eclipse
begins
10:15 UT

Total eclipse
11:54 - 12:06 UT

Partial
eclipse
ends
13:45 UT

Moon enters
penumbra
9:00 UT
(unobservable)

West

A total lunar eclipse has ﬁve stages, with
diﬀerent things to watch for at each.
The ﬁrst penumbral stage begins when
the Moon's leading edge enters the pale
outer fringe of Earth's shadow: the penumbra. But the shading is so weak that
you won't see anything of the penumbra
until the Moon is about halfway across it.
Watch for a slight darkening to become
apparent on the Moon's celestial southeast
side. 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,
where no direct sunlight reaches. With a
telescope, watch the umbra's edge engulf
one lunar feature after another as the
night around you deepens. Eventually
just a ﬁnal bright arc remains outside the
umbra, while the rest is already showing a
foreboding reddish glow.
The third stage is total eclipse, beginning when the last of the Moon slips into
the umbra. But this depends on how the
umbra's edge is deﬁned! The edge is hazy,
and in a grazing instance like this, its

East

Stages of the Eclipse

UMBRA

PENUMBR

South

Eclipse event

EDT

CDT

MDT

PDT

Penumbra ﬁrst visible?

5:35 a.m.

4:35 a.m.

3:35 a.m.

2:35 a.m.

Partial eclipse begins

6:15 a.m.

5:15 a.m.

4:15 a.m.

3:15 a.m.

Total eclipse begins

7:54 a.m.

6:54 a.m.

5:54 a.m.

4:54 a.m.

Mid-eclipse

7:00 a.m.

6:00 a.m.

5:00 a.m.

Total eclipse ends

7:06 a.m.

6:06 a.m.

5:06 a.m.

Partial eclipse ends

7:45 a.m.

6:45 a.m.

Penumbra last visible?

adopted deﬁnition is critical enough that
the U.S. Naval Observatory's Astronomical Almanac lists totality as lasting 12.3
minutes, while Fred Espenak's Fifty-Year
Canon of Lunar Eclipses says 8.6 minutes.
Most of the Moon is sure to glow some
shade of intense orange or red. The red
light shining onto the Moon is sunlight
that has skimmed and bent through
Earth's atmosphere; it's from of all the
sunrises and sunsets that ring our world at
any given moment.
Two factors aﬀect a lunar eclipse's color
and brightness. The ﬁrst is how deeply the
Moon goes into the umbra; the umbra's
center is much darker than its edges.
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 when a major volcanic eruption has
recently polluted the stratosphere with thin

7:25 a.m.

global haze, a lunar eclipse will be dark red,
ashen gray, or occasionally almost black.
In addition, blue light that is slightly
refracted through, and tinted by, Earth's
ozone-rich upper atmosphere can also add
to the scene. These blue rays can create a
subtle mix of changing colors, especially
near the umbra's edge. Time-lapse videos
may also show large "ﬂying shadows" in
the umbra, caused by changing cloud-shadowing eﬀects around the sunrise-sunset
line as Earth moves and turns.
And then, as the Moon continues eastward along its orbit, events replay in reverse
order. The Moon's edge re-emerges into
sunlight, ending totality and beginning
stage four: a partial eclipse again.
When all of the Moon escapes the
umbra, only the last, penumbral shading
is left for stage ﬁve. By about 45 minutes
later, nothing unusual remains at all.
Sk yandTelescope.com April 2015

http://www.skypub.com/charts http://www.SkyandTelescope.com

Sky and Telescope - April 2015

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