Transit of
Mercury
The mighty mite of planets
gets between us and our star
this month.It’s diffi cult to mistake Mercury for a sunspot. Mercury’s silhouette has a
sharp edge and is uniformly opaque, as shown in this image captured by
David H. Timm during the last transit event on May 9, 2016.O
n Monday, November 11th, the
tiny planet Mercury will cross the
face of the Sun as viewed from Earth.
Mercury’s orbit is inclined 7° to the
ecliptic and intersects Earth’s orbital
path at two nodes. The fi rst intersec-
tion (the descending node, when Mercury
is moving south through the ecliptic
plane) occurs near May 8th in the mod-
ern era. The second (the ascending node,
when Mercury is moving north through
the ecliptic plane) falls around Novem-
ber 10th. If Mercury passes through
inferior conjunction at one of those two
times, a transit will occur.
In 2019, the eastern United States,
Canada, and Central America, South
America, and westernmost Africa will
be able to watch the entire event, from
the moment Mercury fi rst “touches”
the Sun to the instant it departs the
Sun’s face. If you’re in western North
America (excluding most of Alaska and
far northern Canada, who won’t see any
of the event), the transit will already
be in progress when the Sun rises. For
most of Africa, Europe, and western
Asia, Mercury’s passage begins in the
daytime, with the Sun setting before the
crossing is complete.
Use the world map on the facing
page to determine your general circum-
stances. The timetable at right shows,
in Universal Time and standard time
for North America, when Mercury’s
leading edge crosses the Sun’s boundary
and when its trailing edge slips from the
Sun. The timings are geocentric, so they48 NOVEMBER 2019 • SKY & TELESCOPE
may differ from local standard times by
a minute or two.
If you didn’t buy a white-light fi lter
for your telescope for the 2017 total
solar eclipse, now’s the time to get one.
The fi lter should fi t snugly on the front
end of your telescope (eyepiece fi lters
aren’t safe!) and be free of defects.
Don’t use a scratched or torn fi lter —
eye damage from sunlight is irreversible.Hydrogen-alpha fi lters are sig-
nifi cantly more expensive and have
a slightly higher learning curve than
white-light fi lters — it takes practice
to produce the best looks at the Sun’s
chromosphere and prominences. But an
H-alpha setup can offer stunning views
of the transit, particularly if Mercury
passes a prominence as it moves onto/
off the Sun’s face.Transit Timetable
Time Zone Transit Begins Transit Midpoint Transit Ends
Universal (GMT) 12:35 15:20 18:04
Eastern (EST) 7:35 a.m. 10:19 a.m. 1:04 p.m.
Central (CST) 6:35 a.m. 9:19 a.m. 12:04 p.m.
Mountain (MST)* — 8:19 a.m. 11:04 a.m.
Pacifi c (PST)* — 7:19 a.m. 10:04 a.m.
Alaskan (AKST)* — — 9:04 a.m.
Hawaiian (HST)* — — 8:04 a.m.
Times for you r location may differ by several minutes. *Transit time begins before sunrise.NOVEMBER 2019 OBSERVING
Celestial Calendar by S. N. Johnson-Roehr