Whether using a telescope or binoculars, solar filters can help you
view the Sun in its best possible light. BY PHIL HARRINGTON
But in order to enjoy the
show, you need to come pre-
pared. The Sun is the only
celestial object that can easily
do you harm. The same solar
rays that cause sunburn will
also burn your eyes’ retinas
— at least, without proper
precautions. We hear these
warnings from our parents
when we’re young and in the
news before every solar
eclipse: Never look directly at
the Sun. So, in order to safely
practice solar viewing, you’ll
need the right equipment.
Most experienced Sun-
watchers prefer specially
designed solar filters that
reduce the Sun’s energy to
harmless levels. Filters come
in two main categories: First
are white-light filters. These
block 99.999 percent of sun-
light to allow us to see theSun’s visible surface, or
photosphere, revealing won-
derful views of constantly
evolving sunspots. Second are
Hydrogen-alpha (Hα) filters.
These block all wavelengths of
sunlight except for one — the
wavelength emitted by hot
hydrogen atoms. Hα filters
reveal details on the Sun that
are invisible using white-light
filters, including f lamelike
prominences and intricate
bright threads called solar
plages, which are usually
found near sunspots.White-light filters
Known as “aperture filters,”
white-light filters fit over the
front of a telescope in order
to reduce the Sun’s energy to
a safe level before it enters the
optical system, including your
eyes. They are commonlyFOR MANY, ASTRONOMY IS A LATE-NIGHT
PURSUIT. We anxiously wait for Sol to set and
twilight to fade before we begin to enjoy the
sky. But by doing so, we are missing an amazing
matinee every day — one performed by the Sun.
Our star is the perfect target for observers. No
chart is needed to find it. You can’t beat it for con-
venience. And light pollution doesn’t even enter
into the equation. With the Sun, there’s no need to
pull an all-nighter. Best of all, it is always changing.
While most distant deep-sky objects appear static
over the course of a human lifespan, the Sun
changes every day. That makes it exciting to watch!
the Sun
made from glass or a polymer
material, such as Mylar, and
fit securely on a telescope or
binoculars (although you will
need two filters for the latter,
one per barrel).
White-light filters should
only be purchased from a
reputable source. Some of
the most popular include
Astrozap (astrozap.com),
Baader Planetarium
(a st rosola r.com /en),Celestron (celestron.com),
Explore Scientific
(ex plorescient i f ic u sa .com),
Kendrick Astro Instruments
(kendrickastro.com), Meade
Instruments (www.meade.
com), Orion Telescopes
(www.telescope.com), and
Thousand Oaks Optical
(thousandoaksoptical.com).
You can purchase a pre-
made filter mounted in a cell
and sized to fit over the frontThese images, taken only 5 minutes apart, show the same part of the Sun’s disk
on September 22, 2009. The photographer took the left shot through a visible-
light filter and the right shot through a Hydrogen-alpha (Hɑ) filter. Note the
additional features visible through the Hɑ filter. DAVID TYLERRIGHT: A Coronado PST, a common
Hɑ telescope, is attached to an alt-
azimuth GoTo mount in this setup —
enabling quick and easy solar
observing. WIKIMEDIA COMMONS/XOFCBELOW: White-light filters, like this
one from Thousand Oaks Optical,
block all wavelengths of light equally,
dimming the Sun enough to reveal
sunspots. THOUSAND OAKS OPTICAL