Solar Photosphere Imaging
University of Colorado at Boulder
The Sun in White Light
| Streaming of the solar
photosphere is broadcast intermittently on May 19th, the
day before the partial solar eclipse (daylight hours and
weather permitting, of course).
Continuous imaging of the Sun began at Noon on May
20th MDT and continues throughout the eclipse
First contact with the Moon occurs at 6:22 pm.
Maximum eclipse happens at 7:30 pm, with 86% of
the Sun's disk covered while only 7 degrees above the
horizon. Sunset occurs about 15 minutes later,
behind the foothills northwest of Boulder, only three
degrees above the astronomical horizon.
Stream videos at Ustream
| This free Ustream webcast is
paid for by the commercials which appear from time-to-time
on your screen.
Ustream Premium Members who log into their account can
watch ad-free by searching for Colorado Astronomy
and/or the channel SommersBauschObservatory Dome.
SBO is also streaming images of the solar
chromosphere on May 20th: see the SommersBauschObservatory
NOTE: Click the "enlarge" button, lower-right
corner of the window, in order to view the solar image
What You Are Seeing
You are looking at live images of the Sun from using a 4-inch
refracting telescope mounted piggyback on the Observatory's 24-Inch B&C
Cassegrain telescope. The refractor has a full-aperture covering of
mylar filter which rejects approximately 99.99% of the sunlight,
making it safe for the camera (and/or eyepiece viewers) to observe
the Sun. Besides attenuating the brightness, however, the view is
exactly the same as one would see with the naked eye (similarly
protected), but merely enlarged for easy viewing.
Telescopes invert images top-to-bottom and left-to-right; hence,
south is up in these images, and west is to the left.
Users watching the eclipse with mylar sunglasses will see the
first "bite" taken out of the Sun from its western (lower-right)
edge of the Sun; that "bite" will appear at the left side of the
"White light"images of the Sun show the visible
atmosphere of the Sun known as the photosphere, or "sphere
of light". Although gaseous throughout, the abrupt decrease in
density and temperature (cooling to a mere 6,000 degrees Kelvin,
hotter than a blast furnace) of the solar atmosphere here makes it
appear that that the Sun has a solid surface. Almost all of the
energy we receive from the Sun is last emitted from this region
before it escapes into space - and reaches us.
Features in the Photosphere
- Sunspots - the most obvious of the visual features,
sunspots are "cool" regions of the Sun (4,000 degrees Kelvin)
which appear relatively dark compared to their surroundings
because the gasses are not as hot. In fact, they are still
brighter than an electric arc. Sunspots mark the regions where
strong magnetic fields emerge from the solar interior; energy
(in the form of charged gas particles, or plasma) is prevented
from efficiently flowing into these areas because they can't
cross the magnetic fields, and so the area cools down. Cooler
areas glow less brightly, and so appear dark.
- Umbra - the darkest, central region of a sunspot, where
the magnetic fields emerge most vertically, The same term is
used to refer to the central dark shadow of the Moon which
results in a total lunar eclipse for observers on Earth.
- Penumbra - the brighter, but still relatively dark,
area of a sunspot surrounding the umbra. Close examination shows
finger-like structures splaying radially away from the umbra as
the magnetic field lines spread. The same term is used in
eclipses to mean the shadow area where the source is only
partially obscured. Hence, for this partial solar eclipse, we in
Boulder are in the "penumbral shadow" of the Moon.
- Granulation - tiny (the size of Colorado) cells of
upwelling gasses from the interior of the Sun, akin to the
cumulus clouds we see develop on Earth when the atmosphere is
heated from below. Exceptionally steady "seeing" is required to
resolve these bubbly features which appear and disappear in a
- Limb Darkening - the decrease in brightness of the
solar photosphere as we look more towards its edge, or "limb".
Here we are seeing less deeply into the photosphere than when
looking straight downward into it from the center: proof that
the atmosphere gets cooler (and hence emits less light) as we go
higher up into the photosphere. (However, this effect changes
abruptly in the overlying atmospheric layers: the chromosphere
and the corona. The physical reasons behind this strange
behavior (higher temperatures the farther away you get from "the
fire") are still not fully understood.