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NJIT
Physics 320: Astronomy and Astrophysics – Lecture X
Carsten Denker
Physics DepartmentCenter for Solar–Terrestrial Research
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Problem 9.9
photon2 2
2 2photon
photon
Electron is initially at rest in reference frame.
1 if 0 1 0!
ee e e
e e
Em v
m vc m c m ccE m c m c
vv E
c
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Problem 9.12
0
2 2
3 3
sds
At wavelength where the opacity is greatest, the value of s is smallest. If the temperature of the star’s atmosphere increases outward, than a smaller value of s corresponds to looking at a higher temperature and a brighter gas. At wavelength where the opacity is greatest, you would therefore emission lines.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Problem 9.13
A large hollow spherical shell of hot gas will look like a ring if you can see straight through the middle of the shell. That is, the shell must be optically thin, and an optically thin hot gas produces emission lines. Near the edges of the shell, where your line of sight passes through more gas, the shell appears brighter and you see in a ring. In 1992 a tremendous explosion occurred in the
constellation of Cygnus. Dubbed Nova Cygni 1992. Astronomers hypothesize that this system's white dwarf had so much gas dumped onto it's surface that conditions became ripe for nuclear fusion. The resulting thermonuclear detonation blasted much of the surrounding gas into an expanding shell.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Exhibition Title Contest
Ian Journey to the Center of
our/your Universe Voyage to the Center of our
Solar System The Sun: More than a
Reason to Skip Class Our Sun: What can it do for
you? Brick City Sun The Key to Live on Earth:
The Sun Our Sun: The Orb of Life The Giant Nuclear Reactor:
The Sun
John The Sun: Our
Closest Star The Sun: A Look
inside our Closest Star
Gerardo, Matthew, & Mike Sunbelievable
Solar Sciene
November 5th, 2003NJIT Center for Solar-Terrestrial Research
The Sun
The Solar Interior Mass Luminosity Radius Effective Temperature Surface Composition
The Solar AtmosphereThe Solar Cycle
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Sun – OverviewMass (kg)
1.989e+30
Mass (Earth = 1) 332,830
Equatorial radius (km) 695,000
Equatorial radius (Earth = 1) 108.97
Mean density (gm/cm3) 1.410
Rotational period (days) 25-36
Escape velocity (km/sec) 618.02
Luminosity (ergs/sec) 3.827e33
Magnitude (Vo) -26.8
Mean surface temperature 6,000°C
Age (billion years) 4.5
Principal chemistry
Hydrogen Helium Oxygen Carbon Nitrogen Neon Iron Silicon Magnesium All others
92.1%7.8%
0.061%0.030%0.0084%0.0076%0.0037%0.0031%0.0024%0.0030%
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Evolution of the Sun and its Interior
Standard Solar Model:
X: 0.71 0.34
Y: 0.27 0.64
Sun–Earth Connection?
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Convection Condition
ln2.5
ln
d P
d T
The Sun is purely radiative below r/R = 0.71 and becomes convective above that point. Physically this occurs because the opacity in the outer layers of the Sun becomes large enough to inhibit the transport of energy.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Differential Rotation and Magnetic Fields
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Active Regions
Active region 9169 was the host of the largest sunspot group observed so far during the current solar cycle. On 20 September 2000, the sunspot area within the group spanned 2,140 millionths of the visible solar surface, an area a dozen times larger than the entire surface of the Earth!
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Spectrum of Granulation
“Wiggly” spectral lines in the solar photosphere inside and outside a region of activity, reflecting rising and sinking motions in granulation. Over the central one third of the spectrogram height, the slit crossed a magnetically active region. Here, the velocity amplitudes are much reduced, demonstrating how convection is disturbed in magnetic areas.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Model of Convection
3D animation of convection. The animation shows temperature fluctuations in a layer of unstable, turbulent gas. (Courtesy of Andrea Malagoli, University of Chicago)
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Mercury Transit November 15th, 1999
The images were taken 20 seconds apart from 21:11 (first contact) to 22:10 UT (last contact). The image were captured with a Kodak MegaPlus 4.2 CCD camera. The spatial resolution is about 1 per pixel. Here, we show only a small portion of the full disk images near the solar north pole. The field of view is approximately 470 170 or 340,000 km 125,000 km on the Sun.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Prominences
The SoHO EIT full sun image, taken on 14 September 1999 in the He II line at 304 Å shows the upper chromosphere/lower transition region at a temperature of about 60,000 K. The bright features are called active regions. A huge erupting prominence escaping the Sun can be seen in the upper right part of the image. Prominences are “cool” 60,000 K plasma embedded in the much hotter surrounding corona, which is typically at temperatures above 1 million K.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Filament Evolution
Temporal evolution in H center line of a sigmoidal filament in active region NOAA 8668 during August 2000.
(a) Videomagnetogram , (b) CaI line wing filtergram, (c) Ha – 0.6 Å filtergram, and (d) Ha center line filtergram.
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Homework Class Project
Continue improving the PPT presentation. Use the abstract from the previous assignment
as a starting point for a PowerPoint presentation.
The PPT presentation should have between 5 and 10 slides.
Bring a print-out of the draft version to the next class as a discussion template for group work
Homework is due Wednesday November 12th, 2003 at the beginning of the lecture!
Exhibition name competition!
November 5th, 2003NJIT Center for Solar-Terrestrial Research
Homework
Homework is due Wednesday November 12th, 2003 at the beginning of the lecture!
Homework assignment: Problems 11.1, 11.2, and 11.8!
Late homework receives only half the credit!
The homework is group homework!Homework should be handed in as a
text document!
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