HOW TO PHOTOGRAPH
THE TRANSIT
To capture Mercury’s solar journey,
use the same equipment and tech-
niques you would to photograph
the Sun at any other time. It’s a good
idea to set up your equipment and do a
trial run before the big day to make sure
you have all the bugs worked out.
On transit morning, focus carefully on the
Sun’s limb and confirm that the image remains
sharp—rising temperatures can result in focus
shift. The Sun will be brightening slightly as it
climbs higher, so you may need to tweak your
exposure settings. Keep an eye on your
camera’s histogram display to ensure
image highlights don’t start to clip.
If you’re lucky enough to have
clear skies all morning, you’ll
have the opportunity to create
a composite portraying the
entire transit, as I did for the
photo on page 22.A shot24 SKYNEWS •NOVEMBER/DECEMBER 2019
TRANSIT HISTORY
Keen-eyed readers will note that after
time-zone differences have been taken
into account, the times listed in our table
differ by 25 seconds across the breadth of
the country. Those few seconds are due
to parallax arising from Canada’s wide base-
line, which causes Mercury’s position to shift
slightly with respect to the Sun, depending
on your viewing location.
It was Edmond Halley (of Halley’s Comet
fame) who realized that by measuring the
parallax shift, it would be possible to calculate
the distance from Earth to the Sun—a value
only approximately known in his day. Halley’s
inspiration came from observing the Mercury
transit of November 7, 1677. He knew a transit
of Venus would prove a more accurate mea -
sure, so he wrote: “Therefore, again and again,
I recommend it to the curious strenuously to
apply themselves to this observation.” And for
the Venus transits of 1761 and 1769, astrono -
mers did just that. Transit teams dispatched
around the globe produced a measure of the
Sun-Earth distance within 3 percent of the
correct value—an achievement to contem-
plate as you watch the solar system’s inner-
most world make its leisurely trek across the
Sun this November.
TRANSIT TIMES Sun’s
Greatest altitude
Location Contact I Contact II transit Contact III Contact IV at egress
St. John’s (NST) 09:05:56 09:07:38 11:50:03 2:32:33 2:34:14 15°
Charlottetown (AST) 08:36:00 08:37:41 11:20:08 2:02:36 2:04:18 20°
Halifax (AST) 08:36:00 08:37:42 11:20:08 2:02:36 2:04:17 22°
Montreal (EST) 07:36:02 07:37:44 10:20:13 1:02:41 1:04:2 2 24°
Toronto (EST) 07:36:04 07:37:45 10:20:15 1:02:43 1:04:24 27°
Winnipeg (CST) ——09:20:20 12:02:52 12:04:33 23°
Regina (CST) ——09:20:22 12:02:55 12:04:36 22°
Edmonton (MST) ——08:20:23 11:02:58 11:04:39 17°
Victoria (PST) ——07:20:26 10:03:02 10:04:43 19°Contact I: Mercury first touches the Sun
Contact II: Mercury tangent to the inside edge of the Sun’s limb at ingress
Greatest transit: Mercury halfway across the solar disc
Contact III: Mercury tangent to the inside edge of the Sun’s limb at egress
Contact IV: Mercury last touches the SunSAFETY FIRSTThe only safe filters for observing the Sun are those
which cover the front aperture of your scope, camera lens or binoculars.
Suitable filters are available as metal-coated glass or aluminized Mylar.
PHOTO BY ALAN DYEREcliptic 8:20 a.m.9:20 a.m.Midtransit
10:20 a.m., EST11:20 a.m.12:20 p.m.Egress ends
1:04 p.m., ESTIngress
begins
7:36 a.m., ESTevery 5 to 10 minutes should suffice. And you can make a time-lapse movie from a
series of individual frames captured at a rate of one image every 30 seconds or
so. An intervalometer automates the task and makes it a lot easier—5½ hours
is a long time to spend minding a camera!
To make aligning frames feasible later, be sure to use an accurately polar-
aligned equatorial mount with its drive set to the solar drive rate. This will
ensure the Sun stays put and doesn’t drift or rotate within the frame.
In addition to gathering stills, you can shoot a movie with either a
DSLR (in movie mode) or a specialized high-frame-rate planetary
camera. Such clips are ideal for capturing the moments of
ingress and egress. For these sequences, use a Barlow lens
to get in close.
To see what’s possible, have a look at my video of the 2016
transit at https://vimeo.com/166750835.STARRYNIGHT™/SIMULATION CURRICULUM