AST 101: The Great Mnemonic Contest Anyone enrolled in AST 101 may enter. You may enter as often as you like. Anonymous entries will be accepted, but cannot be awarded any prizes. Entries must be in English. Entries deemed obscene, racist, or in extremely poor taste will be disqualified. Entries are due, either on paper or by e-mail , no later than 5:00 PM on Friday March 15. Entries may be delivered to your instructor or to your TA. All decisions are final. The winning entries will be announced in class on Friday, March 29. The winning author(s) will be awarded worthless, but tasteful, prizes. The 2013 OBAFGKM Entries Oscar Be A Friend Go Kiss Maria O 'hes Being A Fruitcake, Gonna Knockout Mister Larry Thomas Yaittes Oven Bake And Fire Grill Kepler Meat Only Boring Astronomers Fight Green Killer Martians. Oh Boy! A Furious Goat kicked Mule. Only Because Astronomers Fail Greatly Knowing Many Luminous Types, Yo Offensive Bears Attack! Fearsome Growls! Killing Many Lively Terrestrial Youth!

Omniscient Babies Are Far Guiltier, Knowing Mom Loves to Yodel. Overconfidently Bruised Anarchists Followed Gentle Knights Minus Lonesome Turnips Yesterday. Only Brilliant Astronomers Fix Grave Kepler Mistakes Observable Bright Apparent Formed Giants Keep Magnitude Only Bob Ate Fresh Gummy Karate Monkeys Old Bears Are Fighting Great King Marcus Over Bridges Are Floating gorillas kissing Maidens Old Bald and Fat Guys Kiss More Laddies Than You Other 2013 Entries Man! Various Enemies Made Jaguars Super Undefeatable Now! Many Vegetarians Eat Meat, Just to Stop Under- Nourishment! Manly Vacations Exclude Mailing Junipers South, Upsetting Northerners. My Very Exclusive Mother Just Said the Usually No Rakish Obliging Youthes Guarded Big Icarus Violently. Rich Obedient Yuppies Gored Bruised Irishmen Vastly. Rudely Oily Yummy Goblins Briefed Itchy Vader. Really? Only You Get Broke In Vegas Great Xavier Usually Vacations In Sunny Resorts Good, X Usually Verifies Its Situated Right-here Golden Xylophonic Usher Validated Inexpensive Socrates Reassuringly.

Gleefully Xanthic Ultimate Vamps Impaled Shaggy R2-d2. Gentle Xenophobic User Vilified Icy Supergirl Restfully. Gentle Xylophones Underestimated Opera Including Sleepy Robocop. The 2013 Winners Astronomer's Award: Only Brilliant Astronomers Fix Grave Kepler Mistakes Whittney Silva Cannibal Award: Oven Bake And Fire Grill Kepler Meat Linghua Xu Why we do this Award: Only Boring Astronomers Fight Green Killer Martians. Glenn Thompson Personal Vendetta Award: O 'hes Being A Fruitcake, Gonna Knockout Mister Larry Thomas Yaittes Kevin Lyon Dick Cheney Warmongerer Award: Offensive Bears Attack! Fearsome Growls! Killing Many Lively Terrestrial Youth! Amjed Ka-e Most Interesting Fantasy Award: Over Bridges Are Floating gorillas kissing Maidens Megan Donnelly The Supreme Court Rebuttal Award: Old Bald and Fat Guys Kiss More Laddies Than You Alessandra Vittorini Grand Prize: Oscar Be A Friend Go Kiss Maria Daniel Buchholz Grand Prize in the Roy G. Biv category: Really?

Only You Get Broke In Vegas Dylan Slocki IQ Tests : Letter Sequences - Worksheet / Test Paper Worksheet / Test Paper Hide all answers Hide all answers View all answers View all answers Print Try the Quiz What letter comes in the blank in each sequence below? 1. B, C, D, F, G, H, J, _______ Answer: Answer: K The sequence consists of the consonants (i.e., vowels are omitted). 2. A, D, G, J, M, P, S, _______ Answer: Answer: V The sequence consists of every third letter of the alphabet (i.e., skip two letters in between). 3. A, E, _______, M, Q, U, Y Answer: Answer: I The sequence consists of every fourth letter of the alphabet (i.e., skip three letters in between). 4. A, C, F, J, _______, U Answer: Answer: O The sequence consists of the letters of the alphabet skipping one letter (B), then two letters (D, E), next three letters (G, H, I) and so on. 5.

E, _______, P, T, W, Y, Z Answer: Answer: K The sequence consists of the letters of the alphabet skipping five letter (F,G,H,I,J), then four letters (L,M,N,O), next three letters (Q,R,S) and so on. 6. X, W, C, D, V, U, E, F, _______ Answer: Answer: T When two letters are taken at a time, there are two separate sequences. One sequence is X, W, V, U, T,... (letters of the alphabet backwards) and the other sequence is C, D, E, F, ... (letters of the alphabet forwards). 7. Y, B, X, C, W, D, V, _______ Answer: Answer: E The odd terms are Y, X, W, V (letters starting with Y backwards). The even terms are B, C, D, E (letters starting with B). 8. J, J, H, L, _______, N, D, P Answer: Answer: F The even terms are J, L, N, P (alternate letters starting with J). The odd terms are J, H, F, D (alternate letters starting with D backwards). 9.

A, E, F, H, I, K, L, _______ Answer: Answer: M The sequence consists of the letters of the alphabet with only straight line segments (no curves). 10. B, C, D, G, _______, O, P, Q Answer: Answer: J The sequence consists of the letters of the alphabet with curves. 11. O, T, T, F, F, S, S, _______ Answer: Answer: E The sequence consists of the first letters of the number names (i.e., One, Two, Three, Four, Five, Six, Seven, Eight). 12. J, F, M, A, M, J, J, _______ Answer: Answer: A The Spectral Types of Stars - Sky & Telescope Sky & Telescope Download Your Free Astrophotography Primer Now from Sky & Telescope! * By: Alan MacRobert | August 1, 2006 Mass-producing stellar spectra. A thin prism was placed in front of the telescope to spread out starlight from the Hyades cluster into little rainbows, or spectra. Spectra contain the 'fingerprints' astronomers use to deduce myriad stellar properties.

Click on this image to see some of these stellar spectra up close. University of Michigan Department of Astronomy What's the most important thing to know about a star? Its brightness ( apparent magnitude ) might top the list, but right behind would be its spectral type. Without its spectral type a star is a meaningless dot. Add a few letters and numbers like "G2V" or "B5IV-Vshnne" and the star suddenly gains personality and character. To those who can read its meaning, the spectral code tells at a glance just what kind of object the star really is: its color, size, and luminosity compared to the Sun and stars of all other types; its peculiarities, its history, and its future. The modern spectral classification system is so successful that it has hardly been changed since 1943. It is based on just two physical properties that imprint themselves on the spectrum of a star's light: the star's surface temperature and atmospheric pressure. These reveal an abundance of information that paints the star's portrait and tells its life story. The temperature sets the star's color and determines its surface brightness: how much light comes from each square meter of its surface.

The atmospheric pressure depends on the star's surface gravity and therefore, roughly, on its size — telling whether it is a giant, dwarf, or something in between. The size and surface brightness in turn yield the star's luminosity (its total light output, or absolute magnitude ) and often its evolutionary status (young, middle-aged, or nearing death). The luminosity (when compared to the star's apparent brightness in our sky) also gives a good idea of the star's distance. Appended to the basic spectral type may be letters for chemical peculiarities, an extended atmosphere, unusual surface activity, fast rotation, or other special characteristics. Every starwatcher needs to have a feel for spectral types. Here are the most important things to know. Whether in a star's atmosphere or in a laboratory, absorption lines are produced when a continuous rainbow of light from a hot, dense object (top left) passes through a cooler, more rarefied gas (top center). Emission lines, by contrast, come from an energized, rarefied gas such as in a neon light or a glowing nebula.

S&T / Steven Simpson Dissecting Starlight Our tale began in 1802, when the English experimenter William Wollaston passed a beam of sunlight through a thin slit and then through a prism. The slit provided a sharp, high-resolution view of the familiar rainbow spectrum, with no color overlapping another. When seen this way, Wollaston noticed, the Sun's spectrum was marked by many narrow, black lines of various intensities. These dark lines stayed at exactly the same places in the colorful band from day to day and year to year. They were later measured and cataloged by Josef von Fraunhofer, for whom they are still called "Fraunhofer lines." Similar spectral lines showed up in laboratory experiments. Using a slit and prism, physicists discovered that when a solid, liquid, or dense gas is heated to glow, it emits a smooth spectrum of light with no lines: a continuum. A rarefied hot gas, on the other hand, glows only in certain colors, or wavelengths: bright, narrow emission lines instead of a rainbow band.

If a cooler sample of the same gas is placed in front of a glowing object emitting a continuum, dark absorption lines appear at the wavelengths where the emission lines would be if the gas were hot. British amateur spectroscopist Maurice Gavin obtained this solar spectrum  a 'rainbow' of sunlight with thin, dark absorption lines at numerous discrete wavelengths. Each chemical element creates its own unique set of spectral lines. By 1859 the situation was clear: we see the Sun's hot, relatively dense surface through a cooler solar atmosphere that imposes the dark lines. Here, scientists realized, was a way to bring the Sun down into the laboratory. Every element, every chemical compound, shows its own set of spectral lines. They are as unique as fingerprints. They reveal not only which atoms and molecules are present but also many other physical conditions, starting with temperature. And when astronomers put the same slit-and-prism device (a spectroscope) on a telescope, they could even see spectral lines in the light of stars. It was the 19th century's greatest astronomical breakthrough. Philosophers had cited the makeup of stars as an example of something that was beyond all possible human knowing.

Now finding the composition of the Sun and stars was just a matter of comparing spectral lines seen in a telescope with those seen in a laboratory. This wasn't always simple, but it gave birth to modern astrophysics — the treatment of stars as physical objects to be studied and understood, rather than as mere points of light on the sky to be measured. Ordering Stellar Spectra Early stellar spectra showing the distinctive absorption lines that astronomers used (and use still) to determine stars' compositions and temperatures. This set of spectra comes from the original Henry Draper Catalogue. Harvard College Observatory The first great classifier of stellar spectra was Angelo Secchi, a Jesuit priest in Rome. In the 1860s he examined the spectra of hundreds of stars visually in a telescope and classed them into five main types, mostly named for bright examples. "Sirian" stars, for instance, showed spectra like Sirius's, dominated by absorption lines of hydrogen atoms. Today's classification scheme was born at Harvard College Observatory. Starting in 1886 under Edward C. Pickering, the observatory staff photographed and classified thousands of stellar spectra. They assigned them letters from A through Q, generally in alphabetical order from the simplest-looking to the most complex.

But soon a more natural system became clear. By rearranging and merging classifications, Antonia C. Maury and Annie J. Cannon found that they could fit nearly all stars' spectra into one smooth, continuous sequence. The sequence matched the stars' color temperatures, from the hottest, blue-white stars at one end to relatively cool, orange-red ones at the other. But it was too late to reassign the letters. When the dust cleared, the rearranged sequence ran O B A F G K M from hot to cool. Spectral types on the blue end were called "early" and those on the red end "late." These terms are still used today, though the incorrect idea they embody — that stars simply cool with age — has been obsolete for generations. The sequence could be cut even more finely. Cannon subdivided each letter with numbers from 0 to 9, so that a spectrum whose appearance placed it halfway between standard G0 and K0 stars was called G5. Using this scheme, Cannon led the classification at Harvard of 325,300 spectra recorded on wide-field photographs.

The resulting Henry Draper Catalogue (HD) and Henry Draper Extension (HDE), published beginning in 1918, remain standard references today. Stellar spectra from hot to cool. A star's temperature largely determines which dark absorption lines appear in its spectrum. Although these spectra look like the real thing, they're artificial  the output of a computer model by Roger Bell (University of Maryland) that subjects a solar-type mixture of theoretical atoms to different temperatures at the pressures that prevail in the outer layers of dwarf (main-sequence) stars. Michael Briley, University of Wisconsin, Oshkosh The time-honored mnemonic for remembering the spectral sequence, invented by Henry Norris Russell when astronomy's leadership was all male, is "Oh Be A Fine Girl Kiss Me." In 1995 Mercury magazine published a student's rejoinder: "Only Boys Accepting Feminism Get Kissed Meaningfully." The discovery in recent years of very dim, very red objects — the smallest, coolest red dwarf stars and barely glowing "brown dwarfs" — has led to the creation of three new spectral types past M.

These are L, T, and Y, chosen from among the few remaining letters that might not have some other, confusing meaning. So now the full spectral sequence runs O B A F G K M L T Y. A few other spectral types don't fit the sequence but instead parallel it. Type W or Wolf-Rayet stars are as hot and blue as the hottest O stars but show strong emission lines, either of nitrogen (WN), carbon and oxygen (WC), or neither (WR). Emission lines indicate an especially large, thick shroud of hot gas surrounding these stars. The W stars appear to have blown off their original outer layers of hydrogen, exposing other materials beneath. Some giant stars at the cool end of the spectrum have an excess of carbon. These were originally called R and N but have been merged to form type C. "Carbon stars" can often be spotted at a glance in a telescope by their deep red color. A bright example in the autumn sky is 19 Piscium (TX Piscium) in the Circlet of Pisces, spectral type C5.

Their distinctive absorption bands (masses of overlapping spectral lines) due to the carbon compounds C2, CN, and CH darken or "blanket" the blue end of the spectrum. In other words, a carbon star's atmosphere is a red filter. When seen in emission instead of absorption, these same spectral bands glow blue; the same compounds that redden a carbon star in absorption give comets their blue-green tint in emission. The rare type-S stars are also red giants. They parallel type M but show strong bands of zirconium oxide and lanthanum oxide instead of an M star's titanium oxide. We can imagine that planets of S stars, bathed in chemically peculiar stellar winds, might be encrusted with gems of cubic zirconia. Dwarfs and Giants A Hertzsprung-Russell diagram plots stars' spectral types against their intrinsic luminosities (absolute magnitudes). Most stars lie either on the hydrogen-fusing main sequence or on the giant branch. A scattering of supergiants spans all spectral types. Click for the full view, where many real stars are labeled. Sky & Telescope / Source: James Kaler Even in stars of the same spectral type, the absorption lines don't always look alike.

In some stars the lines are narrow and sharp; in others they are broadened by various different effects. Chief among these effects is atmospheric pressure, which also changes the intensity ratios of certain pressure-sensitive lines. Astronomers quickly realized that atmospheric pressure tells a star's surface gravity and therefore suggests its size. Narrow lines indicate an immense, bloated star with a weakly compressed atmosphere far from its center of gravity. In the Henry Draper Catalogue, spectral types were prefixed with d for dwarf, sg for subgiant, g for giant, and c for supergiant. You'll still run across these letters from time to time, but beginning in 1941 they were replaced by a more detailed scheme first published by William W. Morgan and Philip C. Keenan. With only minor changes, this "MK" system of spectral classification remains the standard today.

Stars are assigned to luminosity classes by Roman numerals: I for supergiants (often subdivided into classes Ia-0, Ia, Iab, and Ib in order of decreasing luminosity), II for bright giants, III for normal giants, IV for subgiants, V for dwarfs on the main sequence (defined in the illustration below), and occasionally VI for subdwarfs. Different atoms and ions leave their fingerprints on starlight at different temperatures. Conditions must be fine-tuned to bring out a given chemical 'fingerprint.' Hydrogen, for instance, only shows up strongly in spectra near type A  even though it makes up the bulk of almost all stars. And hundreds of lines from 'metals' (elements heavier than helium) dominate the spectra of cooler K-type stars, even though metals make up just a tiny fraction of those stars' masses. Sky &Telescope Thus a designation such as G2V, the Sun's spectral type, tells both temperature and luminosity. When these quantities are plotted against each other on a graph, the result (shown at right) is called a Hertzsprung-Russell or H-R diagram.

This has been a fundamental astrophysical tool ever since it was invented around 1911. Most stars gather in certain narrow regions of the H-R diagram according to their masses and ages. Stars arrive on what's called the main sequence soon after they are born, and this evolutionary track is where they spend most of their lives. Massive stars blaze brightly on the hot, blue end of the main sequence. They burn up their nuclear fuel in only millions or tens of millions of years. Stars with lower masses comprise the yellow, orange, and red dwarfs on the lower-right part of the main sequence, where they remain for billions of years. As a star begins to exhaust the hydrogen fuel in its core, it evolves away from the main sequence toward the upper right and becomes a red giant or supergiant. Stars that began with more than eight times the Sun's mass then evolve left and right through complicated loops on the H-R diagram as if in a frenzy to keep up their energy production. Then they finally explode as supernovae. Less massive giants evolve to the left and then down to become white dwarfs; this is the track the Sun will trace through the H-R diagram 8 billion years from now.

Odds and Ends Spectra can reveal many other things about stars. Accordingly, lowercase letters are sometimes added to the end of a spectral type to indicate peculiarities. Here is a partial list: Some Spectral Peculiarity Codes wl Weak lines (suggesting an ancient, "metal"-poor star) Notations can also be added for elements showing abnormally strong lines. For example, Epsilon Ursae Majoris in the Big Dipper is type A0p IV:(CrEu), indicating strong lines of chromium and europium. The colon implies uncertainty in the IV luminosity class. Certain spectral subtleties are not widely known among amateurs. Some visual observers pride themselves on being able to nail a star's spectral type to the nearest letter by its color in the eyepiece. Color is indeed a close indicator of spectral type for stars earlier (hotter) than about K5, at least when no interstellar reddening is present. But the relationship often breaks down among the later K and M stars. Compare the tint of Betelgeuse, type M2 Iab, to that of Aldebaran, K5 III. Most people can't see any difference.

In addition, dwarf G, K, and M stars are not as red as giants and supergiants of the same types. The color difference is equivalent to about one-half to one whole letter class. Look at Orion and his hunting dogs on a crisp December night, and you'll see bright examplars of several spectral classes, from a red M supergiant (Betelgeuse) to a white-hot A main-sequence star (Sirius). Akira Fujii Lastly, differences between spectra are far greater than differences in the actual chemical compositions of stars. An A star might seem to be almost pure hydrogen, while a K star shows only trace evidence of hydrogen in a spectrum packed with lines of "metals" (the astronomer's term for all elements other than hydrogen and helium). But A and K stars are in fact made of the same stuff. Different atoms and ions merely display their spectral lines at different temperatures. Even carbon stars are made mostly of hydrogen and helium. The true "abundances" of elements can indeed be measured in a star. But it's a tough job of comparing precise line strengths in a high-quality spectrum with the strengths predicted by atomic theory or measured in the lab.

For much of the 20th century, the study of visible-light spectra practically was astronomy. In recent decades the opening of nonvisible wavelengths and other exciting advances have distracted attention from this field. Nevertheless it remains the bedrock on which modern astronomy rests. CATEGORIES SOLUTION: What should be the next letter in the following series? A Z E B I Y O _ SOLUTION: What should be the next letter in the following series? A Z E B I Y O _ Algebra -> Sequences-and-series -> SOLUTION: What should be the next letter in the following series? A Z E B I Y O _ Question 470074 : What should be the next letter in the following series? A Z E B I Y O _ This is more a puzzle than it is a problem in mathematics. . That being the case you need to look at the pattern in the series. . Starting with the first letter in the series (letter A) every other following letter in the series is the next vowel, so every other letter beginning with the A should follow the pattern A, E, I, O, U . Then starting with the second letter in the series (letter Z) the pattern is that every other letter following it will be a consonant.

The next consonant after the Z (which is the first consonant at the end of the alphabet) is the first consonant at the beginning of the alphabet (letter B). And the consonant following the B is a Y which is the next consonant in descending order from the Z. And two letters after the Y, the next consonant appears. It is the letter C because that is the first consonant in ascending order from B. . Note that the consonants are working their way toward the middle of the alphabet. Every fourth consonant following the letter Z is the next consonant downward in the alphabet. And starting with the letter B, every fourth consonant following the B will be the next consonant upward in the alphabet. . Maybe this is enough to explain what I saw as the patterns. There may be other patterns also, but this one can be sufficiently explained to make it a possible solution. . All the above rationale being the case, the series can be extended by adding in sequence the letters C and U and X. So the series becomes: . A Z E B I Y O C U X . 3) What's the next letter in the sequence: P O I U Y T R E W?

- Quora Quora Written Jul 14, 2013 Get married and have kids. I understand this isn't considered a "mistake" by most people, on the contrary, it's considered a bliss (especially when children are involved). But it's definitely a mistake for me. I know myself. I know I'll never be a good wife, and certainly not a good mother (I don't like kids... I'd rather have dogs or cats... kids are annoying little monsters). I'm too selfis... Logical Reasoning Test Sequences (Logical Reasoning) Test This test involves letter sequences and tests your ability to think logically and analytically. Some employers use similar tests as part of their selection procedures and this test will give you some idea of what to expect. The test has 27 questions and you will have 12 minutes to do them. At the end of the test (when 12 minutes have elapsed), you will be given a score. You can still continue answering questions for practice after this point, but your score will not change. The test will start with two example questions which will not be marked or timed.

Look at the sequence and work out which of the five numbers below it is the next member of the sequence. Now click on the "First Question" button below to begin. Click on the button beneath your answer to answer it. You can change your answer by clicking on another button.You can also go back to the previous question, by clicking on the previous question button. When you have finished the test click on "Get Your Score" The alphabet is given below to help you: a b c d e f g h i j k l m n o p q r s t u v w x y z WHAT YOUR SCORE MEANS As mentioned before, this test is for practice only, so you should not regard your result as of importance chiefly because the test was not taken under proper test conditions e.g. in a silent room with no disturbances. Your performance can also be distorted if you have a cold, or have not slept well. Also, evidence shows that international students or those from ethnic minorities may be disadvantaged in this type of test, due to language and cultural differences. If your first language is not English, your score is likely to be lower on verbal tests than native English speakers.

Mature students may also sometimes be disadvantaged and you should remember that your degree subject may change your performance - for example scientists are likely to do better on mathematical tests and Humanities students on verbal tests. Even your ability to use a mouse may influence your score! Having said all this it is still natural for you to want some feedback on your performance. Score 22 or above. This is an above average score compared to other Kent graduates who have taken the test. 17 - 21. This is in the average group compared to other Kent graduates who have taken this test. 16 or below. This is below the typical score of Kent graduates who have taken the test, but remember that a number of factors may have distorted your score - see above for some of these factors. You may wish to discuss your results with a careers adviser. Take free tests at Graduates First For further example tests and help with tests, see our Aptitude Tests page with tips on how to pass tests. There are now several free practice aptitude tests available on the University of Kent Careers web site.

The tests are Numerical Reasoning , Numerical Test 2 slightly harder graphs and tables test, Verbal Reasoning , Verbal (Synonyms) , and Diagrammatic/Spatial The answers to this test are not confidential and are as follows (answer numbers refer to the option choice between 1 and 5): star - What is the origin of the OBAFGKM classification system? - Astronomy Stack Exchange What is the origin of the OBAFGKM classification system? Once a body has been identified as a star it is classified into a subsection of either O,B,A,F,G,K or M (I think there are also 3 more letters recently added) What is the origin of this classification system? Do each of the letters stand for anything?

1 Just an interesting note : The mnemonic used to remember the sequence is "O Be A Fine Girl Kiss Me" – Cheeku Sep 28 '13 at 1:46 up vote 6 down vote The Wikipedia article on stellar classification has the full list of letters: Class | Surface Temperature --------------------------- O | > 33,000 K B | 10,000 - 33,000 K A | 7500 - 10,000 K F | 6000 - 7500 K G | 5200 - 6000 K K | 3700 - 5200 K M | 2000 - 3700 K L | 1300 - 2000 K - T | 700 - 1300 K | These are those new letters Y | < 700 K - History This Cornell doc explains much of the history behind the system: In the 1890s, many scientists were interested in developing a classification scheme for the stars. Edward C.

Pickering at Harvard University, together with his assistant Williamina P. Fleming, assigned stars a letter according to how much Hydrogen could be observed in their spectra: stars labeled A had the most Hydrogen, B the next most, and so on through the alphabet. There were 22 types in all: this scheme was rather cumbersome, and it wasn't clear what its physical significance was. In 1901, another of Pickering's assistants, Annie Jump Cannon, also begun to work on the classification sequence. Her meticulous observations led her to simplify the 22-type scheme into a simple sequence of temperature: OBAFGKM. Not only was the scheme much simpler than the previous, but it related the amount of hydrogen observed to a physical property of the stars for the first time. Spectral Classes Spectral Classes Luminosity Classes The rapid spread of spectroscopy in the late Nineteenth century resulted in a large number of stellar spectra. Astronomers faced the major challenge of trying to make sense of them. This was analogous to the problem faced earlier in the biological sciences and tackled by Linnaeus through his classification system of living organisms.

The system now used was adopted in 1910 following detailed and extensive work by Annie Cannon and her team at Harvard Observatory. It has been refined since then but in essence is still the same. To see how this spectral classification scheme works study the sequence of spectra shown below. It shows spectra for different stars as photographic plots. In reality photographic spectra would not show colour as the plates were monochrome but the colour has been added here to highlight the different wavelengths. Continuum K2V M0V If you study the spectra above you will notice some trends. The 0-class spectrum has relatively weak lines but lines for ionised He+ are present. The B, A and F stars have a similar pattern of lines that are strongest in the A star. These are the H Balmer series for neutral hydrogen. F and G stars have lines corresponding to ionised Ca+. The K and M stars have many more lines visible but the Balmer series is very weak. These lines correspond to Fe, other neutral metals and molecules. TiO lines are visible in the spectrum of M stars. Another way of comparing stellar spectra is by studying their intensity plots. The sequence below is for main sequence stars from about the middle of each spectral class.

It shows the spectrum for a small region of the visible waveband from 390 - 450 nm. Credit: Adapted from data in Project CLEA Classification of Stellar Spectra Exercise. Why do different stars have different lines? This question is the key to helping us classify stars. If we compare an O-class star with and M-class star they have very different lines. The O-class star has weak lines except those for ionised He+ and it also has a continuum that is strong in the UV region. The key factor at work here is temperature. By temperature we really mean the effective temperature of the star (sometimes called the surface temperature). This is the temperature of a black body having the same size and luminosity as the star and is determined by Stefan's Law. The variations in spectral lines for different stars are due primarily to the difference in temperature of the outer layers of gas in the star. In very hot stars, helium can be ionised so we can expect to see spectral lines due to absorption by helium ions. In most stars the temperature is too cool for helium to ionise so no such lines can form in the spectrum.

Even though spectral lines due to helium are not found in cool stars it does not mean that helium is missing from the star. In fact helium is the second most abundant element in the Universe and in stars. The absence of helium lines simply means that the conditions are not right for helium lines to form or be abundant in that star. Some stars are cool enough that molecules can exist in outer layers without being ripped apart. As the number of possible electron transitions is much greater in molecules than single atoms there are many possible spectral lines that can form hence cool stars typically have many lines. The standard spectral class classification scheme is thus based on temperature. Most stars fit into one of the following types or spectral classes: O, B, A, F, G, K, M These classes go from hot to cool with O the hottest and M, cool. recent discoveries have led to tentative new classifications for even cooler L-class stars. For the moment, however, we will focus on the seven original classes. The letters assigned to each class seem confusing and out of order. This is an historical artefact as classes were assigned to spectra before the underlying physical relationship was known. Rather than reassign letters to different spectra, some classes were merged and the whole sequence arranged in order of decreasing temperature.

How can you remember the sequence? Many people use a memory device or mnemonic to help them. Here is a common example but feel free to make up your own. Oh Be A Fine Girl (or Guy), Kiss Me! The basic system of a letter to denote spectral class is further refined by adding a number from 0 to 9 following it. Each spectral class is thus broken down into ten subdivisions so that, for example, an F2 star is hotter than an F7 star. The basic characteristics of each spectral class are summarised in the following table. The four columns on the right of the table provide comparison of a star's mass, radius and luminosity (power output) with respect to the Sun and the main sequence lifespan for a star of that spectral class. These factors are discussed in more detail in later sections of the site. Spectral Class Summary May or may not be fusing H in cores? Some stars exhibit spectral anomalies resulting in them being given special classifications: R-class stars have the same temperature as K-class stars but have high abundances of carbon and carbon molecules. N-class stars are carbon-rich stars with the same temperature as M-class stars.

S-class stars are similar temperature to M stars but have bands of zirconium oxide and lanthanum oxide. WN and WC are two types of Wolf-Rayet stars, the same temperature as O-class stars but showing strong broad emission lines of carbon and nitrogen respectively. Luminosity Classes One problem facing early attempts at classifying stellar spectra was the fact that two spectra could have the same lines present, indicating that the stars had the same effective temperature, but the lines in one star's spectrum were broader than in the other. When the star's were plotted on an HR diagram it also became apparent that two stars could have the same effective temperature (hence also colour and spectral class) but vary enormously in luminosity and thus absolute magnitude. To account for this a second classification scheme of Luminosity Class was added to the original concept of Spectral Class. A simplified version of the MK system of luminosity classes is shown in the table below. Luminosity Classes of Stars ASTRonomy 103 ASTRonomy 103 Sample Examination #3 The spectral types of stars utilize the letters A B F G K M O.

Arrange in order from COOLEST to HOTTEST: A O-B-A-F-G-K-M A occurs when a white dwarf's mass exceeds the Chandrasekhar limit B is the result of helium flash C is characterized by a spectrum that shows hydrogen lines D occurs when the iron core of a massive star collapses E c and d An astronomer observing a star cluster in the Galaxy could do which of the following to determine the age of the cluster? A construct an HR diagram for the cluster B count the number of cepheids in the cluster C measure the Doppler shifts of many stars in the cluster D wait for a supernova in the cluster and measure its light curve E check the radial and transverse velocities The planetarium dome is right now emitting its own light primarily in what wavelength region? A gamma rays D visible E X-rays Suppose you were watching an unfortunate fellow astronaut falling into a black hole.

Compared to your ship's master clock, the watch on her wrist, as you see it (and while you still can see it), would be running A backwards D at the same rate E none of the above is true After a second red giant stage, an old solar-mass star will gently eject its outer layers, leaving behind a hot, small stellar A nova D supernova remnant E T Tauri A star that is cool and faint will fall in what part of an HR diagram? A lower left D upper right E more information is necessary to answer When the solar core has mostly been transformed from hydrogen into helium the Sun will move to the next phase of its evolution, changing gradually into a A different type of main sequence star B planet Which of the following do astronomers use to discover possible black holes?

A dark regions in the sky B red-shifted optical spectra C spheres of orbiting photons D strong X-ray emission E the slowing of clocks Pulsars are believed to be A pulsating neutron stars A B-type star leaves the main sequence due to A exploding as a supernova B the exhaustion of hydrogen in its core C the onset of helium burning D the onset of the CNO cycle E none of the above Up to 90 percent of a star's mass can be thrown off in a supernova explosion. The remainder of the star will be a A black hole D more than one of the above is possible E none of the above is possible After a low-mass star runs out of hydrogen in its core, it begins burning hydrogen in a shell around the core. The next main event that changes its structure is A helium burning starts in the core B the outer layers are ejected and nuclear burning stops C the star explodes as a supernova D the star runs out of hydrogen completely E carbon burning starts in the core An HR diagram is a plot of what two stellar properties?

A absolute magnitude and luminosity B age and mass D mass and absolute magnitude E temperature and spectral type A new star begins to form when A an existing star is broken apart B an interstellar cloud collapses by its own gravity C fresh material falls onto the core of a previously-dead star D nuclear reactions start inside a large planet E new stars don't form anymore In the Sun's final phase of evolution it will become a A black hole D any of the above are possible E pulsar The following table gives the name, absolute magnitude, apparent magnitude, and spectral type for five stars. Answer the following six questions using this table and the appropriate letter corresponding to the star that is best described by the line given. Note that stars/letters may be used more than once. Star Name M m SpT A Aldeberan -0.5 +0.9 K5 III B Antares -3.8 +1.0 M2 I C Deneb -7.2 +1.3 A2 I D Fomalhaut +2.0 +1.2 A3 V E Spica -3.5 +1.0 B1 III Which star appears brightest in the sky? Which star is intrinsically the brightest?

Which star is hottest? Which star is farthest away? Which star is a red supergiant? Which star has the largest radius? The most important factor in determining the main sequence lifetime of a star is its A radius E none of the above The mass-luminosity relation indicates that A bright main sequence stars are more massive than faint main sequence stars B giants are more massive than main sequence stars C giants are more massive than white dwarfs D main sequence stars are more massive than white dwarfs E all of the above Unlike low-mass stars, massive stars A do not run out of hydrogen in their cores before they die B eventually burn carbon in their cores C never burn helium in their cores D never burn hydrogen in their cores E end their lives by fissioning the of Uranium A star that is cool and bright will fall in what part of an HR diagram?

A lower left E there exist no such stars A supernova explosion may cause A a nearby cloud of gas to collapse to form a new star B a nearby cloud of gas to form a planetary nebula C other nearby stars to become neutron stars or black holes D other nearby stars to explode as supernovae E fission to occur In the HR diagram, most stars lie on the main sequence because A all stars spend most of their lives there B most stars have been born very recently C other stars are not plotted on the HR diagram D other stars are very faint and hard to see E other stars prevent them leaving the diagonal Neutron stars A are among the brightest stars we know of B obey the mass-luminosity relation C obey the period-luminosity relation D often emit radio waves in two narrow beams E none of the above The spectral types of four stars are listed below. Which star has the largest radius? A A5 V A a flat disk of material around a protostar B an expanding shell of gas around a dying star C .the evaporation of a planet when a star becomes a red giant D the final state of a star having a very small size E is a disk around a planet What is the net result of the proton-proton chain?

A helium is fused into carbon and energy is released B hydrogen is fused into helium and energy is released C interstellar molecules are formed D interstellar clouds begin to collapse to form stars E a chain of protons Protostars are difficult to observe because A the protostar stage is very short B they are surrounded by cocoons of gas and dust C they radiate mainly in the infrared D all of the above E they are all so far away that the light hasn't reached us yet Atoms of cool hydrogen emit 21-cm radiation when the A electrons move from the fourth to the second energy level B electrons move from the second to the fourth energy level C protons in neutral helium change their spin D electrons in neutral hydrogen change their spin E hydrogen atoms adds a second electron to form H Molecular clouds can be observed A using infrared telescopes to detect ionized gas in the clouds B using x-ray telescopes to observe the x-ray radiation from the molecules in the cloud C using radio telescopes to observe the CO emission from the clouds D by looking for blue wispy regions near star clusters E by looking for the 21-cm radiation from hydrogen The extinction of starlight due to the interstellar medium I. is the greatest in the ultraviolet.

II. is the greatest in the infrared. III. is caused by ionized hydrogen. IV. is caused by dust particles.

Question: In astronomy, what is the next letter in the sequence O, B, A, F, G, K
Answer: M