Astrophotography @
The Sun
Goals
•
•
Photograph the sun in full/natural color and observe sun spots
Photograph the sun using appropriate filters to observe solar prominences.
DO NOT LOOK AT THE SUN
DO NOT TRY TO PHOTOGRAPH THE SUN WITH
YOUR CAMERA
DON’T EVEN
THINK ABOUT POINTING
of this is the blue/UV portion of the sun light. If
the sun is near the horizon (setting or rising),
then there is enough atmosphere to attenuate
the blue components. This is why it’s possible
to photograph a sunset, or why you’re not
permanently blinded driving into a setting sun.
YOUR CAMERA AT THE SUN.
UNLESS YOU ARE USING SPECIAL EQUIPMENT
THAT PERMITS THIS AND YOU HAVE BEEN
INSTRUCTED ON ITS PROPER USE.
Better safe than sorry. ☺
It is said that the father of modern astronomy,
Galileo Galilei, went blind from looking at the
sun with a telescope. These are half-truths.
Yes, he did look at the sun through telescopes,
but only at sunrise and sunset. And, yes, he
went blind; from a combination of cataracts and
glaucoma at age 72. There is a lot of literature
on this, but the simplest piece of evidence is the
following: Most astronomers look through a
telescope consistently with one eye. Galileo
went blind in both eyes, at the same time.
So, is it safe to look directly at the sun? It
depends. The short answer is that if it’s
uncomfortable, then it’s not safe. And don’t do
it. The damage that can occur to the unaided
eye (no telescope) is photochemical in nature
and not necessarily thermal. The primary cause
In this project, however, we will be
photographing the sun when it is nearly
overhead. This means that there is very little
atmospheric filtering and potentially dangerous
to our eyes and cameras. Furthermore, a
telescope will gather even more light making
the risk of permanent thermal damage almost
certain. An 8” Celestron telescope will collect
over 1000 times more energy than just the
entrance pupil of your eye. Even a brief,
accidental gaze into the finder-scope of the
instrument can be damaging. The point: care
must be taken.
Natural Color Sun/Sunspots.
In this project, we will place a solar filter over
the telescope entrance. This will block 99.99%
of incoming sunlight so you can safely observe
the sun and sunspots without damaging your
eyes or camera. This filter does not change the
color of the image. We will use the prime focus
technique again with the telescope. By the
way, the finder-scope on the telescope will be
removed so that no accidental damage can
occur.
Depending on the activity of the sun, we should
see small sunspots. Sunspots are cooler areas
of the sun. They appear black compared to the
rest of sun but are actually dark red. Spots are
caused by strong magnetic fields disrupting the
flow of energy outward to the surface of the
sphere. The sun goes through a natural 11 year
cycle of sunspot activity.
The Sun with many large sunspots. Image credit: Solar and
Heliospheric Observatory (SOHO) taken Sept. 27, 2001
The sun as photographed with f=55mm, f/5.6, 1/100”,
ISO3200, through a solar filter.
Sunspots are easy to see when the sun is active.
Solar prominences, on the other hand are much
fainter. A prominence is an ejection of material
from the sun’s surface (the photosphere). They
are often seen anchored to the surface, and
frequently making large loops back to the
surface due to strong magnetic fields.
To photograph prominences, we will highlight
these by a judicious choice of color filtering.
Since the surface of the sun is comprised mostly
of hydrogen, we will use a special filter that
selects a color very specific to hydrogen: 656nm,
a red. Sometimes this is called the “hydrogenalpha” (H-α) line.
The Sun (also transit of Venus 6/5/12) Celestron C8, f=2032
mm, ƒ/10, 1/200”, ISO800 and solar filter. Not many
sunspots that day.
The visible light spectrum comprising white light.
The Hydrogen spectrum. From red to blue, these are
frequently called the α, β, and γ lines and so on.
A standard photographic filter is not sufficient
for this work. They allow too much other light
(other colors) through. The telescope used for
this project uses a combination of technology
that allows very precise control of the color of
light passing through. Said in more technical
terms, a photographic filter is too broad band.
The telescope in this project uses an etalon has
a resolution of 0.7nm.
When the telescope is properly adjusted, the
only light that is transmitted is the desired H-α
light. This highlights many processes on the sun
including prominences. When a prominence is
viewed from a different perspective so that it is
against the sun instead of the backdrop of
space, it appears darker than the surrounding
background. This formation is instead called a
solar filament.
Canon EOS 5D Mk II, 1/13”, ISO3200 using a Coronado
SolarMax 90 H-α telescope. Note the prominences at the
limbs of the sun, and filaments near the center of the disk.
A Coronado 90mm telescope with special H-α filters.