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Faces of the Sun
Please check http://www.noao.edu/outreach/resource/sun.html for a list of websites on the sun.
PART I → PREPARATION FOR SOLAR OBSERVING
Never look directly at the Sun through a telescope!!
1. Watch the demo of your instructor. Explain what would happen to your eyes if
you looked at the Sun through a telescope.
2. You will be looking at a “projected” image of the Sun. What do you expect to see?
Faces of the Sun  Page 1
PART II → SOLAR FEATURES
A) DRAWING SOLAR FEATURES
1. Carefully draw the projected image of the Sun including any features you see
Do this part later
1 mm on this image = ___________ km on the Sun
The Earth = ____________ mm on this scale.
2. Give a brief written description of all those features. (Write full sentences!) Comment on
intensity changes across the surface of the sun. Comment on the number, size and separation
between sunspots. Describe the structure of the largest sunspot.
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B) THE SIZE OF SUN SPOTS
1. Five students will measure the size of the sun’s projected diameter with a ruler. Copy the
measurements below, then average.
__________ __________ __________ __________ __________
Average linear diameter (in cm) is
_________ cm
2. The Sun’s and the Earth’s Radii are:
•
•
RSun = 6.96 x 105 km (700,000 km is accurate enough)
REarth = 6378 km (6400 km is accurate enough)
Calculate the image scale of the projection. [Hint: One cm in projection corresponds to ?? km]
3. Measure the size of the largest sunspot (in cm) in the projection with a ruler. Five students will
take 5 measurements across a different area of the sunspot. Record these below.
__________ __________ __________ __________ __________
Average diameter (in mm) is _________ mm or _________ cm
4. Calculate the diameter of the sunspot on the Sun in km.
5. Calculate the scale of the image you drew. [Hint: One mm in your drawing corresponds to ?? km
on the Sun]. Write the scale into the box in your drawing on the previous page.
6. Calculate the size of the Earth in your drawing an write this into the same box in your drawing.
How many Earth’s can you fit into the largest Sun spot? Draw this into your picture.
7. Spell out how the size of a sunspot compares to the size of the Earth.
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PART III → LIGHT AT DIFFERENT WAVELENGTHS
A) BASICS ABOUT LIGHT
Light is electromagnetic radiation. Light is generally characterized by its wavelength (the distance
from crest to crest) or frequency (the number of crests passing per second). The “Visual” (visible
light) is only a small part of the electromagnetic spectrum of light. The spectrum has a much wider
range of wavelengths than we can see ranging from Gamma, to X-Ray to UV to Visual, to Infrared,
to Microwaves to Radio Waves. Please consult page 11 of the TOOLKIT where there is picture of
the electromagnetic spectrum.
You will be looking at light taken with a specific filter – the Hα filter – that shows dominantly
hydrogen gas of a specific temperature. It is as if you are wearing glasses that only let you see a small
part of the red light.
If we had different eyes we could also see other parts of the spectrum. For example, cats and owls
can see infrared light (the longer wavelength light) – they can see in the dark. However when we take
picture with infra red sensitive films we can “see” the infra red like in the pictures below.
Images taken from http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/index.html
Furthermore, we can not see the UV light of the spectrum, nor any of the shorter wavelengths, such
as X-rays and Gamma rays. In fact too much X-ray light is harmful. The Sun emits much light in the
X-ray region of the electromagnetic spectrum, but we are lucky since the Earth’s atmosphere shields
up from a large fraction of this harmful radiation. That’s why, if we do want to study the Sun in the
UV & X-ray, we have to mount telescopes onto satellites outside the Earth’s atmosphere. Your
teacher will show you some UV images of the Sun. They will look rather unfamiliar because we
normally cannot see this light. You’ll be looking at these UV images, describing them, labeling them,
and drawing some conclusions.
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B) LEARNING ABOUT FILTERS
Put on the glasses your instructor has provided.
If you close one eye and only look through the
red filter, you will see all red color variations,
and if you close the other you will see all the
blue tones. Look at the picture to the right
through the red and the blue filters and describe
how the images look different.
This image of an aurora is taken from
http://www.davidmalin.com/.
The red and blue images below have been matched to what you would see through the glasses.
Though the difference is more impressive with the glasses, the red and blue pictures also do illustrate
that different features stand out when you look through the red and the blue filters. If you take away
the color information like in the black & white pictures below the differences between the images
still stands out, and some would argue, is even more striking.
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Again, put on the glasses your instructor has provided and look at the pictures below, first through
the red, then through the blue filter. Look at each of the images separately (while covering the
remaining ones with paper). These images are taken from
http://www.davidmalin.com/miller/miller_index.html.
Describe which colors look bright and which look dark when you look through the red filter.
Describe which colors look bright and which look dark when you look through the blue filter.
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C) ANALYZING Hα IMAGES
Your instructor will add an H-alpha (Hα) filter to the telescope. This is a filter that only lets through a
narrow range of wavelengths of red light and blocks the rest. With this filter you will see only the
light that is emitted by the cooling hydrogen gas. So you see gas only of a particular temperature
range. Look though the telescope.
1) Draw what you see into your image of the Sun on page 2.
2) Invent names for the structures and label then in your diagram of the Sun.
3) Describe what you see. Comment on structures, shapes and locations of individual features. Also
describe higher and lower intensity regions.
4) Assuming that these structures are on the entire surface of the sun, why do you think you only see
these structures on the limb of the sun, why not over the entire disk?
5) Look at the high contrast Hα image your instructor is showing you. What are the dark filaments
that appear in the high contrast Hα image of the sun? Why are these filaments dark?
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D) ANALYZING UV IMAGES
Look at the four color coded UV images that your instructor has provided (remember you cannot see
the UVs – but the camera that took the picture could). The four images were taken with four different
filters: shorter, medium, long and longer wavelengths in the UV – this is like using blue, green,
yellow, and red filters in the visual spectrum. Each time you look at the same thing, but different
features may stand out through each filter – similar to what you observed when looking through the
red-blue glasses your teacher provided.) It turns out that the red image shows gas that is 60,000K hot,
the blue image 1 million degree gas, the green image 1.5 and the yellow image over 2 million degree
gas. The yellow image shows the hottest gas that is farthest (roughly one solar radius) from the sun’s
white light surface. The red image shows (still very hot) gas in the chromosphere. This is illustrated
in the diagram below that is taken from http://www.windows.ucar.edu/.
The image below taken from http://sohowww.nascom.nasa.gov/gallery/ is a composite image of the
combined images that you will analyze separately.
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1) Describe the features that you see in the blue colored UV image. Comment on differences in
intensity. Describe individual structures and filaments.
2) Invent names for these structures. Label those structures in the UV images.
3) Compare this image to what you drew before. How does it look different? What looks similar?
Can you find the large sun spot you measured in the previous exercise? Label that sunspot in the
UV image. What other common features can you identify in the Visual and UV images?
3) The yellow UV image shows the hottest gas, the green, blue and red subsequently cooler (but still
very hot) gas. Comment on the parts of the loops that are hottest. Comment on the locations and
temperatures of coronal holes (dark region in all images).
4) How has seeing the UV images of the Sun changed your perception of the Sun?
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PART IV → MOVIES OF THE SUN
A) STRUCTURE OF THE SUN
Your instructor will show you a series of movies. But before you see them please look at the images
below and read the text. The images and the text below are descriptive – they are intended to remind
you of the different views of the sun, identify characteristic features, and introduce you to technical
terms. No explanations are given – these can be found in your textbook.
Æ Label all features in your drawing and in the UV images with the correct names.
a) A slice through the Sun
The first picture is a schematic drawing, the second one drawn more to scale, and the third one shows
the corona (and the solar wind), with the central regions blocked out.
corona The tenuous outer atmosphere of the Sun,
which lies just above the chromosphere, and at
great distances turns into the solar wind.
photosphere The visible surface of the Sun, lying
just above the uppermost layer of the Sun's interior,
and just below the chromosphere.
chromosphere The Sun's lower atmosphere, lying
just above the visible photosphere.
transition zone The region of rapid temperature
increase that separates the Sun's chromosphere
from the corona.
convection zone Region of the Sun's interior, lying
just below the surface, where the material of the
Sun is in constant convective motion (see images
on next page). This region extends into the solar
interior to a depth of about 200,000 km.
radiation zone Region of the Sun's interior where
extremely high temperatures guarantee that the gas
is completely ionized. Photons are only
occasionally diverted by electrons, and travel
through this region with relative ease.
Faces of the Sun  Page 10
b) Solar Features and their Definitions
granulation Mottled appearance of the
solar surface, caused by rising (hot)
and falling (cool) material in
convective cells just below the
photosphere.
spicules Spike-like outflows from the
photosphere Short-lived narrow jets of
gas that typically last mere minutes.
sunspot A dark blemish found on the
surface of the Sun. The dark color of the
sunspot indicates that it is a region of
lower temperature than its surroundings.
Sunspots show an umbra, or dark center,
surrounded by a grayish penumbra
active region Region of the
photosphere of the Sun surrounding
a sunspot group, which can erupt
violently and unpredictably.
prominence Loop or sheet
of
glowing gas ejected from an active
region, which then moves through the
inner parts of the corona under the
influence of the Sun's magnetic field.
coronal mass ejection Ejection of mass from a prominence
flare Very energetic and sudden event
occurring in or near an active region.
coronal hole Vast regions of the Sun's
atmosphere where the density of matter is
about 10 times lower than average. The
gas there streams freely into space at high
speeds, escaping the Sun completely.
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B) WATCHING AND ANALYZING MOVIES
Describe what you notice in each movie.
1) Movies and Pictures of sunspots. Describe the properties of sunspots and how they evolve.
2) Movie on UV and Visual images. Describe what you see. [Hint: compare the locations of sun
spots and active regions.]
3) Movie on Solar Wind. Describe what you see. Is this a surprise to you?
4) Two movies on Solar granulation & convection. How are granulation and convection correlated?
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5) Two movies on Solar Minimum & Maximum. Describe what you understand by the term differential
rotation. How is it related to sun spot activity. What are the differences between solar minimum and
maximum?
6) Three movies on loops. Describe the structure of the prominences. Speculate on the connection
between the prominences and magnetic activity of the Sun.
7) Two movies on Solar Flares. Describe How long do they last? What do you think the speckles in
the green movie are? How are they correlated to the flare activity?
8) Four movies of Flares and Coronal Mass ejections. Describe the Coronal Mass Ejection. What do
you think what effect this Solar Ejection could have on Earth?
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PART V → HOMEWORK
Write a scientifically correct 1 to 2 page fictional story of your choice. Include the following terms:
Solar Activity, Sunspot, Flare, Prominence, Explosion, Coronal Mass Ejection, Differential Rotation,
Magnetic Field, Solar Cycle.
Faces of the Sun  Page 14