?In this lab you examine various features of the Sun and determine some of its behavior.
These links are information to be considered and analyzed in the lab report.
with reference to Influence on Earth SOLAR IRRADIANCE OVER TIME
The radiant energy output of the Sun is called the ?solar constant.? Actually, the output is not precisely
constant, but varies some with time. Many people have wondered whether the variation in the Sun?s
radiant output could be responsible for a major part of global warming. This question can be studied by
referring to the website ?http://www.pmodwrc.ch/pmod.php?topic=tsi/composite/SolarConstant?, where the
subject is ?Solar Constant: Construction of a Composite Total Solar Irradiance (TSI) Time Series from
1978 to present.? Here we are interested in the Sun?s brightness (that is, solar irradiance) over time.
At that website the following graph is shown. The units of measurement are watts per meter-squared,
symbolized as Wm?-2?, and the term for this measure is ?irradiance?. The graph here shows only 30 years of
data. But other information is available concerning solar irradiance further back in time. The sizable error
bars shown in the figure here are related to the fact that solar irradiance cannot be measured well at
ground level, because the atmosphere intervenes and is variable. Instruments need to be outside the
Earth?s atmosphere. But problems arise when comparing data from different instruments on board
different satellites, resulting in some uncertainty about long-term changes in solar irradiance. Figure 1. Solar irradiance over 30 years.
The variations in output coincide with the Sun?s sunspot cycle ? the output is highest at the peak of the
sunspot cycle. (The sunspot cycle is discussed and illustrated in the next section.) With respect to global
warming, the solar irradiance on average over the past 30 years is not increasing, during the time when
Earth?s temperature has been rising. Obviously, the bulk of recent global warming is not due to rising
solar irradiance, even though many global warming detractors claim that the Sun is the major cause. SUNSPOT CYCLE
Sunspots were first detected with primitive telescopes several hundred years ago, although it is probable
that they were seen earlier, by many human beings, with the unaided eye. Although the Sun is too bright
to observe most of the time, sometimes the conditions permit direct observation by eye. When the Sun is
low on the horizon and the atmosphere is very humid, almost cloudy, the Sun appears as a red disk, and is
dimmed enough to view for seconds or even minutes without causing eye damage. At such times, spots
can be seen with the unaided eye if vision is acute (this writer has seen them on several occasions), and
this can be verified easily with binoculars or telescopes.
With a filtered telescope and diffusing screen an image of the bright Sun can be observed on a screen
without eye protection. Sunspots can then be counted. Observations reveal a cycle in the number of
sunspots visible at any time, and from good records the cycle is shown to have a period of 11 years from
peak to peak.
Data for the past 300 years are shown in the following graph. Figure 2. Sunspot numbers for the past 300 years. The 11-year cycle is very apparent.
Early reports of sunspots were disbelieved on grounds that God?s creation is perfect and hence cannot
have included sunspots. However, sunspots from a scientific view involve magnetic fields. ?Sunspots are
surface concentrations of the star's magnetic field and the more there are, the more energy the Sun is
emitting.? The magnetic polarities of sunspots reverse from cycle to cycle.
Sunspot numbers have been ?recorded regularly since 1610.? Sunspot numbers for previous times can be
determined from ice cores and tree rings. ?These contain isotopes, such as carbon-14 and beryllium-10,
created when high-energy particles from deep space, called cosmic rays, slam into the atmosphere. Fewer
cosmic rays reach the Earth when the Sun is very active, because the charged particles from the Sun
deflect them.? In 2004 a research team in Germany obtained carbon and beryllium data from trees
preserved in riverbeds and bogs to obtain yearly sunspot numbers for the past 11,400 years.? 1 Maggie McKee, "Sunspots more active than for 8000 years," NewScientist.com news service, 27 October 2004. See also
Nature 431:1047,1084, 2004. EXERCISE #1 ? Determine the Solar Period of Rotation
Sunspots can be used to determine the period of rotation of the Sun. Simply count the number of days for
spots to be carried from one edge of the visible Sun to the other, and multiply by two to obtain the period.
This is a simplistic method; more sophisticated methods determine sunspot locations on the 2-dimensional
solar image and convert those positions to angular positions on the spherical Sun?s three-dimensional
surface, and calculate the solar period from those angular positions. For exacting measurements the effect
of the Earth?s orbital motion must be taken into account, and the possibility of spot migration on the solar
To do Exercise #1, you have some choices. (1) You can go to the site where the original images and video
are located, at ?http://www.astr.ua.edu/ay102/Lab7/Lab_7_Rotation.html?. The animated GIF file first
encountered on that site (Figure 7.16) shows a sequence of images in quick succession.
(2) The same GIF file has been doctored and copied on to Blackboard under the Lab 7 folder, to show
each image for 4 seconds. With this long interval, the spots on each image can be examined leisurely.
From days and times marked on some images, the amount of time for sunspot travel can be determined,
and from that time the solar period can be determined. Determine the solar period from several spots, and
average the results.
(3) It is possibly most convenient to use, instead of the 4-second GIF file on Blackboard, the display of
still images (Figure 7.17) at the above original website, positioned below the animated gif display.
Perform this exercise for 3-5 sunspots, and average the results.
Compare your average result with the known solar rotation period? at the equator of 25.38 days. This
is the ?sidereal? period as seen from outer space, not from the Earth. As seen from Earth, the solar period
is 27.2753 days, different from the sidereal period because of Earth revolution.
Also, note carefully that because the Sun is a giant ball of plasma, and not solid, the rotational period
varies with its latitude. Thus, careful measurements of the rotational period are expressed in terms of
latitude. Using sunspots to determine the period at different latitudes is complicated by the fact that
sunpots generally form at high latitudes and move during their lifetime toward the solar equator.
You may want to comment on the above details when analyzing your average result and comparing to the
known solar rotation period. CORONAL MASS EJECTIONS (CMEs)
CMEs are ejections of massive amounts of hot gas from the solar surface. CMEs are released during solar
flares and prominences, and occasionally from a relatively quiet solar surface. Figure 3 shows an example
of a solar prominence. Prominences may last for months, while flares are short-term bursts of radiant
energy. Flares are associated with sunquakes having Richter magnitudes possibly as high as 11. (Recent
study suggests that flares and prominences are of one type on a continuum, and that CMEs from them 2 have three generative stages. ? Tarbuck and Lutgens do not mention CMEs, and distinguish between flares
and prominences. ?) CMEs if directed earthward disrupt communications and cause magnificent displays
of ?aurora borealis? (the ?Northern Lights?). CMEs are strong enough to burn out sensitive electronics on
satellites in Earth orbit, and to endanger surface instruments as well. Figure 3. Giant solar prominence at 1-2 o?clock position. EXERCISE #2 ? Determine CME directions for July 16-22, 2002
At the website ?http://www.astr.ua.edu/ay102/Lab7/Lab_7_CME.html?, examine the three smaller images
showing eastward, earthward, and westward directed CMEs. The center image is an animated GIF which
clearly shows the character of an earthward-directed CME as observed from Earth ? the cloud of particles
streaming toward Earth spreads in roughly circular pattern as the cloud of particles approaches Earth.
Examine the image sequence in the larger-size frame of an animated GIF file further down the website
page. It covers the range of dates from July 16 to July 22, 2002. This sequence has been slowed down and
a copy named ?Corona_movie.gif? has been posted on Blackboard under the Lab 7 assignment. In this
slowed version, it is easier to observe the details of the eruptions. For best results open this animated file
in Internet Explorer. Beware of its size at 22 Mb.
Look for all major CMEs that occurred during July 16-22, 2202. There are at least 3 CMEs and possibly
more. Determine the general direction of travel away from the Sun for each CME ? eastward (defined in
the website as to the left), earthward, or westward (defined as to the right), or other directions. Put the
results in a table with 2 columns, one for the date, and the second column for the direction of CME travel. 2 Joan Feynman and Alexander Ruzmaikin, "A High-Speed Erupting-Prominence CME: A Bridge Between Types," ?Solar
Physics 219 (2) 301-313, February 2004.
Edward J. Tarbuck and Frederick K. Lutgens, ?Earth Science, 11th?? edn., Upper Saddle River, NJ: Pearson Prentice Hall, 2006,
pp. 653-654. PHOTOSPHERE, CHROMOSPHERE AND CORONA
The photosphere, about 500 km or 300 miles in thickness, is the solar ?surface? emitting most the
radiation seen from Earth. (The solar radius is 700,000 km.) Above the photosphere is the chromosphere,
a few thousand kilometres thick, and therefore much thicker than the photosphere but much less dense,
separately seen only during a solar eclipse using special apparatus. Still higher is the corona, extending a
million kilometres from the Sun. The bright region seen during a total solar eclipse is the corona.
The more than 60 elements in the solar material are indicated by the colors of light they emit when hot.
For example, sodium emits distinctive yellow spectral lines, while hydrogen emits red, blue and violet
spectral lines. By study of the light from the photosphere and chromosphere, it has been found that white
light (all colors combined) emanates from the photosphere, while the lower and upper chromosphere can
be selectively viewed using filters that isolate the spectral lines from calcium and from hydrogen,
respectively. The figures below show images obtained in different colors ?
white light from the photosphere,
calcium emission generally from the lower chromosphere, and
hydrogen emission generally from the upper chromosphere. EXERCISE #3 ? Describe features of the Photosphere and Chromosphere
Examine each image below and record the features that you see in each image. Identify the solar part
(photosphere, chromosphere, ?etc.) where each feature is being observed. Keep in mind that hotter regions
in the images show as brighter and lighter in tone.
Here is a list of the features you should look for. Some of the features will be visible in more than one of
1. granulation? ? ?convective cell structures ... visible in white light (?rice grains?). Each cell
consists of a brighter polygonal area of hot rising gas typically about 1100 km across, and a cooler
edge or ?channel? of descending gas about 230 km wide.? (See the Hinode imagery under ?Solar
Dynamics? in the Lab 7 Blackboard folder);
2. sunspots? ? the very dark umbra; and lighter surrounding penumbra;
3. brightness mottling ("?faculae?") ? ?A bright area on the face of the ?Sun?, commonly seen near an
active region?, such as a ?sunspot?, or where such a region is about to form. Faculae, which last on
average about 15 days, are best seen in blue light and are not visible at all in ?H-alpha?. They were
named by Johannes ?Hevelius? and are thought to be caused by luminous hydrogen clouds close to
4. bright patches called "?plage?" marking areas of moderately strong magnetic fields; ?patchy
H-Alpha brightening on the solar disk, usually found in or near active regions, which can last for
several days. Plage is irregular in shape and variable in brightness, marking areas of nearly vertical
emerging of reconnecting magnetic field lines.?; 4 Quotations are from http://www.daylightastronomy.com/Calcium-K/Daylight_Astronomy_Calcium-K.htm and from
http://www.daviddarling.info/encyclopedia/F/facula.html. 5. bright spots of upwelling gas delineating "supergranulation" cells (?patterns of ?convective? ?cells
where hot gas is coming up from below, and forming a network, larger in size than typical
8. spicules? ? flame-like or bush-like structures that extend upward into the corona, usually seen best
at the edge of the solar disk;
9. flares? ? white regions within a plage;
10. directional ?lineation? indicating ?magnetic? ?field? lines.
A convenient way to report the features that you see would be to form a table. Form a table with
several columns and rows. Include a row for each feature, and a column for each section of the
Sun being examined (photosphere,? chromosphere, ?etc., and the name of the type of light seen in
the image).. There should be a separate column for each one of the images below. The leftmost
column is for the names of the features (choose a word or two as identifiers for each feature ? for
example, the top row in the first column could contain ?granulation?). Figure 4. Image in Calcium-K spectral line.
From http://www.daylightastronomy.com/Calcium-K/Daylight_Astronomy_Calcium-K.htm. Figure 5. Image in Hydrogen-? Spectral Line. The image has been specially processed to remove
limb darkening (in the previous and following images see limb darkening ? toward the edges of
the disk, the Sun is not as bright). From http://www.bbso.njit.edu/images.html. Figure 6. Image in Hydrogen-? Spectral Line.
From http://blog.swanastro.org.uk/2012_08_05_archive.html. Figure 7. Image showing faculae in the lower chromosphere and upper photosphere.
From http://www.daviddarling.info/encyclopedia/F/facula.html. Figure 8. Simultaneous images in white light, calcium-K, and hydrogen-? spectral lines.
The image can be copied from this document and enlarged to show better detail. LAB REPORT
Complete a lab report in the standard format. Now that you have had practice in writing lab reports, the
formatting in this one should be ?impeccable?. If there are any questions about formatting, consult the
formatting directions in the Lab Report Format document under Assignments / Before You Begin.
Include the results of all three exercises from above. Provide appropriate discussion of all results.
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