Xavier thinks to himself, "Very thick."

Mithos raised his hand "Its about 3300 km thick."

Kay raised her hand. "The solar atmosphere consists of, from the innermost part outward, the photosphere, the chromosphere, the corona, and the expanding outer layers of the corona that astronomers call the solar wind.

The photosphere is the visible part of the Sun and is about 300 km (200 mi.) thick. The chromosphere is about 2,000 to 3,000 km (1,200 to 1,900 mi.) thick and is located above the photosphere. The corona and the solar wind are estimated to be millions of km thick.

We look right through the chromosphere, the corona, and the solar wind, just as we see through Earth’s atmosphere at night."

jessie, raised her hand "The Earth's atmosphere is a thin layer of gases that surrounds the Earth. It composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and trace amounts of other gases. This thin gaseous layer insulates the Earth from extreme temperatures; it keeps heat inside the atmosphere and it also blocks the Earth from much of the Sun's incoming ultraviolet radiation.
The Earth's atmosphere is about 300 miles (480 km) thick, but most of the atmosphere (about 80%) is within 10 miles (16 km) of the surface of the Earth. There is no exact place where the atmosphere ends; it just gets thinner and thinner, until it merges with outer space.

Mark raised his hand "it is 330 km thick."

That's right, 3 points.

There are 7 main characteristics that scientists look for when classifying a star. Who can name them?

Nadia raised her hand, "The brightness, the declination of the star, the right ascension, the distances to a nearby star, absolute magnitude, spectral type, and the proper motion, I believe. Also, I think it's considered to which constellation it's part of and the position/coordenates and an specific year."

In more detail: "Many of the brighter, or otherwise interesting, stars have Proper Names, derive from Arabic, and there are also a few Latin ones, such as Polaris, and even a few English ones, such as Barnard's Star. Johann Bayer introduced a system of designating the brightest stars in each constellation by means of Greek (or less often) Latin letters, a system which is still widely used. In principle, the brightest star of the constellation should be given the designation Alpha, the next brightest Beta, and so on. John Flamsteed's numbering of stars within constellations have also remained popular and it gave the star's relative location from west to east within the constellation. Variable stars which do not have Bayer designations are given special designations which mark them out as variable stars. In the absence of any better means of designating a star, catalogue numbers are generally used.

The Bonner Durchmusterung star names include the initials of which of the four catalogues they are from, followed by the angle of declination of the star and an arbitrary number as there are always thousands of stars at each angle.

Names in the SAO catalogue start with the letters SAO, followed by a number. The numbers are assigned following 18 ten-degree bands in the sky, with stars sorted by right ascension within each band.

A common way of detecting nearby stars is to look for relatively high proper motions. To include yet more stars, constellations are dropped and the stars are named according to position, generally right ascension, or angle to the east of the vernal equinox.

There are different classifications of stars ranging from type O which are very large and bright, to M which is often just large enough to start ignition of the hydrogen. Some of the more common classifications are O, B, A, F, G, K, M,Each letter has 9 subclassifications. Our Sun is a G2, which is very near the middle in terms of quantities observed. Most stars fall into the main sequence which is a description of stars based on their absolute magnitude and spectral type.

The specialty Hipparcos Catalogue is also of general use. The Hipparcos satellite was flown in the 1990s to measure precise distances (through accurate parallaxes) to nearby stars.

Other cathaloges for naming stars include characteristics such as basing it in positions, magnitudes in various optical passbands, star/galaxy estimators, star's coordinates, photometric data, spectral types, the secular variation, the proper motion, the weighted average absolute parallax and its standard error, the number of parallax observations, quality of interagreement of the different values, the visual magnitude and cross-identifications with other catalogues."

5 points to Nadia.

Well you got a few, but the list I was going for was Magnitude, Luminosity, Spectral Type, Effective Temperature, Size, Mass and Chemical Composition.

What is apparent magnitude?

Kay raised her hand. "Apparent magnitude of a star is a number that tells how bright that star appears at its great distance from Earth."

"The apparent magnitude of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object.
"One hundred times less bright (e.g. the same object ten times as far) corresponds to an apparent magnitude that is five more; 2.512 times less bright (e.g. the same object 1.585 times as far) corresponds to an apparent magnitude that is one more, 2.512 being the fifth root of 100 (1000.2)."

Magnitude is the degree of brightness of a celestial body or star that is designated on a numerical scale. The brightest star has a magnitude of -1.4 and the faintest visible star has a magnitude of 6. The scale rule shows that a decrease of one unit represents an increase in apparent brightness by a factor of 2.512.

Mark was sitting down and sceching because he didint know the anwser

Jenna sat silent, furiously scribbling notes in her notebook.

Excellent, 5 points.

What about luminosity?

*raise hand* "In general physics, luminosity (or luminance) is the density of luminous intensity in a given direction. In astronomy, luminosity is the amount of energy a body radiates per unit time. It is typically expressed in the SI units watts, in the cgs units ergs per second, or in terms of solar luminosities, Ls; that is, how many times more energy the object radiates than the Sun, whose luminosity is 3.827×1026 W.

"In measuring star brightnesses, luminosity, apparent magnitude (brightness), and distance are interrelated parameters. Luminosity is an intrinsic constant independent of distance, while in contrast apparent brightness observed is related to distance with an inverse square relationship. The sun's luminosity is the standard."

Excellent! 3 points.

Next, Spectral type. What is the instument called that measures the spectral type of a star?

sushant barges in through the door, he has been running from prof dru. he comes in and falls on the prof and getting scared runs back out

OOC: Ok... Since when was I promoted to professor? And why wasn't I informed???

BIC: Dru puts up her hand. "Astronomers determine the spectral type of a star by passing the star’s light through an instrument called a spectroscope. "

Solar radiation instruments are used for the measurement of the spectral range of radiation.
The most common is the pyranometer that measures global solar radiation (sun + sky), or daylight radiation. There is also the radiometer, that measures the net radiation level, or the sum of the incoming direct beam and diffuse solar radiation minus reflected solar radiation. Third is the quantum sensor, which measures the photosynthetic light spectrum or Photosynthetic Photon Flux Density (PPFD), the number of photons incident per unit type on a unit surface.

oops

Any more disruptions to my class and I will start taking off points!

Thats correct, 2 points.

Effectinve temperature - Every star varies in temperature from that of the core, the temperature of which is measured in the millions of degrees, to that of the atmosphere that is relatively cool. For example, the Sun's core reaches 15 million degrees C, while its outer layer is about 5800° C. Astronomers determine the temperature of a star's surface by comparing its spectrum with that of a black body (a theoretical body that perfectly absorbs all the radiation striking it). Scientists know how to correlate a black body spectrum with its temperature. From the known temperature of the black body spectrum that agrees most closely with the star's spectrum, astronomers can determine the star's surface temperature.

Size and mass really don't need an explanation, but what does chemical composition mean?

Kali raised her hand and answered, "Chemical composition applies to what chemicals and elements make up a certain object. For example, the atmosphere has a chemcial composition of nitrogen, oxygen, and other trace elements and gases. The same applies to stars. They can be made up of a different chemcial composition of gases-- the popular ones being hydrogen and helium."

Kay raised her hand. "Chemical composition is the unit cell of any substance will contain one or and integral multiple of chemical formula units. Mineral formulas are based on the relationship to unit cell volume and the positions of atoms within the unit cell.

The calculation of the chemical composition is straight-forward. The molecular weight from the empirical formula divided by the sums of the atomic weights of each element to yield the percentage of each element. This is done for each element in the empirical formula and tabulated as the chemical composition. Please note the sort order is based on the electro-negativity of the element.

Additional information provided is the chemical composition expressed as the % oxide of the element. These data are provided to help in the comparison of mineral analyses which use oxide percent. The convention of reporting the oxide percent dates back to when minerals and rocks were analyzed using wet-chemical methods to precipitate an element. The precipitate was oxidized under high temperature and the results were weighed as the oxide."

Nadia raised her hand, "The chemical composition of a substance refers to the elements of which the substance is composed. For example, common table salt is composed of sodium and chlorine." Nadia paused. "I supposse that in Astronomy, in the stars, the chemical composition means the levels of hydrogen, helium and other gasses."

Awesome, 5 points.

I think that is enough for now. We will continue part 2 of this lesson in a few days. Homework will be given then.