A birthstone is the "gemstone associated with the date of one's birth, the wearing of which is commonly thought to bring good luck or health. Supernatural powers have long been attributed by astrologers to certain gemstones."
- from Encyclopedia Britannica
Birthstones come in a colorful array of sparkling jewels and glowing gemstones, each one with its own place in history and myth. From folklore tales, Biblical texts, and the annals of history, these gems have had a special place in both the hearts and minds of humanity.
Discover historical facts, origins, trivia, fun facts, myths, and more about each month's birthstone by selecting the month of your choice from the menu at the left.
Birthstone List: A quick list of birthstones for each month and the birthstone colors for each month.
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Birthstone ListJanuary Birthstone
January Gemstone: Garnet
January Birthstone Color: Deep Red
(Nov. 24, 2010) — Following a study of what is in effect a miniature galaxy buried inside a normal-sized one -- like a Russian doll -- astronomers using a CSIRO telescope have concluded that massive black holes are more powerful than we thought.
An international team of astronomers led by Dr Manfred Pakull at the University of Strasbourg in France has discovered a 'microquasar' -- a small black hole, weighing only as much as a star, that shoots jets of radio-emitting particles into space.
Called S26, the black hole sits inside a regular galaxy called NGC 7793, which is 13M light-years away in the Southern constellation of Sculptor.
Earlier this year Pakull and colleagues observed S26 with optical and X-ray telescopes (the European Southern Observatory's Very Large Telescope and NASA's Chandra space telescope).
Now they have made new observations with CSIRO's Compact Array radio telescope near Narrabri, NSW. These show that S26 is a near-perfect analogue of the much larger 'radio galaxies' and 'radio quasars'.
Called S26, the black hole sits inside a regular galaxy called NGC 7793, which is 13M light-years away in the Southern constellation of Sculptor.
Powerful radio galaxies and quasars are almost extinct today, but they dominated the early Universe, billions of years ago, like cosmic dinosaurs. They contain big black holes, billions of times more massive than the Sun, and shoot out huge radio jets that can stretch millions of light-years into space.
Astronomers have been working for decades to understand how these black holes form their giant jets, and how much of the black hole's energy those jets transmit to the gas they travel through. That gas is the raw material for forming stars, and the effects of jets on star-formation have been hotly debated.
"Measuring the power of black hole jets, and therefore their heating effect, is usually very difficult," said co-author Roberto Soria (University College London), who carried out the radio observations.
"With this unusual object, a bonsai radio quasar in our own backyard, we have a unique opportunity to study the energetics of the jets."
Using their combined optical, X-ray and radio data, the scientists were able to determine how much of the jet's energy went into heating the gas around it, and how much went into making the jet glow at radio wavelengths.
They concluded that only about a thousandth of the energy went into creating the radio glow.
"This suggests that in bigger galaxies too the jets are about a thousand times more powerful than we'd estimate from their radio glow alone," said Dr Tasso Tzioumis of CSIRO Astronomy and Space Science.
"That means that black hole jets can be both more powerful and more efficient than we thought, and that their heating effect on the galaxies they live in can be stronger."
This two-panel graphic contains two composite images of galaxies used in a recent study of supermassive black holes. In each of the galaxies, data from NASA's Chandra X-ray Observatory are blue, and optical data from the Sloan Digital Sky survey are shown in red, yellow and white. The galaxy on the left, Abell 644, is in the center of a galaxy cluster that lies about 1.1 billion light years from Earth. On the right is an isolated, or "field," galaxy named SDSS J1021+1312, which is located about 900 million light years away. At the center of both of these galaxies is a growing supermassive black hole, called an active galactic nucleus (AGN) by astronomers, which is pulling in large quantities of gas. (Credit: X-ray: NASA/CXC/Univ of Washington/D.Haggard et al, Optical: SDSS)
(Dec. 20, 2010) — A new study from NASA's Chandra X-ray Observatory tells scientists how often the biggest black holes have been active over the last few billion years. The object could help scientists better understand how massive stars explode, which ones leave behind black holes or neutron stars, and how many black holes are in our galaxy and others.
This discovery clarifies how supermassive black holes grow and could have implications for how the giant black hole at the center of the Milky Way will behave in the future.
Most galaxies, including our own, are thought to contain supermassive black holes at their centers, with masses ranging from millions to billions of times the mass of the Sun. For reasons not entirely understood, astronomers have found that these black holes exhibit a wide variety of activity levels: from dormant to just lethargic to practically hyper.
The most lively supermassive black holes produce what are called "active galactic nuclei," or AGN, by pulling in large quantities of gas. This gas is heated as it falls in and glows brightly in X-ray light.
"We've found that only about one percent of galaxies with masses similar to the Milky Way contain supermassive black holes in their most active phase," said Daryl Haggard of the University of Washington in Seattle, WA, and Northwestern University in Evanston, IL, who led the study. "Trying to figure out how many of these black holes are active at any time is important for understanding how black holes grow within galaxies and how this growth is affected by their environment."
This study involves a survey called the Chandra Multiwavelength Project, or ChaMP, which covers 30 square degrees on the sky, the largest sky area of any Chandra survey to date. Combining Chandra's X-ray images with optical images from the Sloan Digital Sky Survey, about 100,000 galaxies were analyzed. Out of those, about 1,600 were X-ray bright, signaling possible AGN activity.
Only galaxies out to 1.6 billion light years from Earth could be meaningfully compared to the Milky Way, although galaxies as far away as 6.3 billion light years were also studied. Primarily isolated or "field" galaxies were included, not galaxies in clusters or groups.
"This is the first direct determination of the fraction of field galaxies in the local Universe that contain active supermassive black holes," said co-author Paul Green of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "We want to know how often these giant black holes flare up, since that's when they go through a major growth spurt."
A key goal of astronomers is to understand how AGN activity has affected the growth of galaxies. A striking correlation between the mass of the giant black holes and the mass of the central regions of their host galaxy suggests that the growth of supermassive black holes and their host galaxies are strongly linked. Determining the AGN fraction in the local Universe is crucial for helping to model this parallel growth.
One result from this study is that the fraction of galaxies containing AGN depends on the mass of the galaxy. The most massive galaxies are the most likely to host AGN, whereas galaxies that are only about a tenth as massive as the Milky Way have about a ten times smaller chance of containing an AGN.
Another result is that a gradual decrease in the AGN fraction is seen with cosmic time since the Big Bang, confirming work done by others. This implies that either the fuel supply or the fueling mechanism for the black holes is changing with time.
The study also has important implications for understanding how the neighborhoods of galaxies affects the growth of their black holes, because the AGN fraction for field galaxies was found to be indistinguishable from that for galaxies in dense clusters.
"It seems that really active black holes are rare but not antisocial," said Haggard. "This has been a surprise to some, but might provide important clues about how the environment affects black hole growth."
It is possible that the AGN fraction has been evolving with cosmic time in both clusters and in the field, but at different rates. If the AGN fraction in clusters started out higher than for field galaxies -- as some results have hinted -- but then decreased more rapidly, at some point the cluster fraction would be about equal to the field fraction. This may explain what is being seen in the local Universe.
The Milky Way contains a supermassive black hole known as Sagittarius A* (Sgr A*, for short). Even though astronomers have witnessed some activity from Sgr A* using Chandra and other telescopes over the years, it has been at a very low level. If the Milky Way follows the trends seen in the ChaMP survey, Sgr A* should be about a billion times brighter in X-rays for roughly 1% of the remaining lifetime of the Sun. Such activity is likely to have been much more common in the distant past.
If Sgr A* did become an AGN it wouldn't be a threat to life here on Earth, but it would give a spectacular show at X-ray and radio wavelengths. However, any planets that are much closer to the center of the Galaxy, or directly in the line of fire, would receive large and potentially damaging amounts of radiation.
These results were published in the Nov. 10 issue of The Astrophysical Journal. Other co-authors on the paper were Scott Anderson of the University of Washington, Anca Constantin from James Madison University, Tom Aldcroft and Dong-Woo Kim from Harvard-Smithsonian Center for Astrophysics and Wayne Barkhouse from the University of North Dakota.
NASA's Marshall Space Flight Center in Huntsville, Ala., manages the Chandra program for NASA's Science Mission Directorate in Washington. The Smithsonian Astrophysical Observatory controls Chandra's science and flight operations from Cambridge, Mass.
Minds On Physics is more than 1300 carefully-crafted questions designed to improve student conceptions of common physics topics. Minds On Physics is 135 challenging sublevels, each of which address one or two student learning outcomes. Minds On Physics is a collection of 15 modules which are designed to provide students with a learning opportunity, an exercise in thinking, and a chance to reflect and review.
Minds On Physics is hard to describe because Minds On Physics is like nothing else. At first glance, it appears to be an exercise in answering questions. But it is indeed much more than that. Students will certainly answer questions and they will definitely get an exercise. The exercise is an exercise in thinking, an exercise in pondering the meaning of a concept, an exercise in probing the relationship between ideas, and an exercise in making sense of the language which is used to express a physics principle. Students will get a mental workout as they think about how they conceive of a topic. Common misconceptions are often targeted. Superficial thinking is quickly challenged. And a deeper understanding of a concept is most often the end result of this exercise in Minds On Physics.
The Minds On Physics Internet Modules utilize a collection of carefully crafted questions to challenge students' misconceptions concerning physics concepts. Interactive Shockwave files have been combined with web-based instructional resources to assist students in becoming aware of and altering their conceptual understanding of the world of motion, waves and electricity. Fifteen learning modules composed of varying levels of difficulty have been created. Students progress through each level of the modules by correctly answering questions which are randomly selected from a bank of several questions. Immediate feedback, and direct links to web-based instructional resources (The Physics Classroom and the Multimedia Physics Studios) are provided. Students having difficulty with a given question can link directly to question-specific help for that question. The success of a student on any given module can be checked using a system of encrypted success codes.
The Shockwave Files - How They Work
The Shockwave files are created with a multimedia authoring product known as Macromedia Director (now called Adobe Director). Director includes a scripting language known as Lingo. Each Shockwave file contains a bank of up to 50 questions. Lingo scripts are used to select a question from the bank, evaluate student answers, check on student progress on a sublevel and provide feedback and directions to the student. In effect, Lingo is the quarterback which directs the plays while the various questions and graphics are the players which show up on the field at Lingo's command. Upon the successful completion of a sublevel, an encrypted success code is generated based on name and ID information. This success code can be used to validate that a student completed the assigned sublevel(s).
The original Minds On Physics Internet Modules were constructed during the summer months of 1999 by three physics teachers - Tom Henderson, Neil Schmidgall, and Brian Wegley - from Glenbrook South High School in Glenview, IL. The project was supported by an NSTA/Toyota Tapestry grant - a generous grant provided by Toyota Motor Sales and administered by the National Science Teachers Association. With the grant money, software was purchased to develop the modules and summer stipends were provided to support the work of the three teachers. An online FileMaker Pro database was used to automatically track student progress through each module. The following school year, nine modules on mechanics topics were ready for use by the Glenbrook South physics students.
Both teachers and students were instantly amazed by the ability of the modules to improve student understanding. Teachers marveled at the student interest over the modules and the high levels of cognitive engagement when working on the modules. Students found the modules both educational and fun. They often begged teachers to take them to the computer lab to work on "MOP". Some of those original students claimed to have become MOP-aholics.
The original modules suffered from a variety of design problems which were gradually fixed over the next couple of years. Additionally, seven other modules were developed to support students in the electricity, waves, and ray optics portion of the course. The Minds On Physics Internet Modules were originally created to be used with a web-connected database. The database collected information regarding student progress in any given module. This database arrangement allowed Glenbrook South physics teachers to make assignments and easily check on students' completion of the assignment for the purpose of assigning grades. In recent years, the database has no longer been used; instead, a system utilizing encrypted success codes is used for the purpose of holding students accountable for completion of assigned work. These success codes are based upon the student name and ID number and thus unique to every student. The use of such success codes allow both Glenbrook South teachers and teachers from other schools to assign work and to check on student completion of sublevels.
Use of the Minds On Physics Internet modules requires a single piece of web browser technology which are available free of charge. First, you will need to have version 7.0 (or higher) of the Shockwave plug-in. Shockwave is available free of charge from Download section of the Adobe web site. Directions for installation are provided there. Installation is highly automated and should take no more than a couple of minutes. Your role in the installation process will merely require that you select the version for your operating system and answer a few simple questions (name, e-mail address, etc.).
Minds On Physics should work in any browser which supports the Shockwave plug-in. Most browsers do. At this writing, the one notable exception is the Firefox browser.
One common technical problem associated with the use of the modules involves the "You are using an illegal version ..." message. Some code has been included in the log-in file which prevents people from downloading the file to their computer or to another server and doing Minds on Physics "offline" or as a program that is separate from the www.physicsclassroom.com website. If a user attempts to use MOP without the file being served from The Physics Classroom server (and a few other "allowed" servers), then the message "You are using an illegal version ..." appears and MOP freezes at the log-in page. Occasionally a school or a home network is set up in such a way that the browser first checks to see if the page has been visited sometime in the past X days. If it has, the file is served to the computer from the school server or from the local hard drive (where it has been cached). This is done to save the little time it takes to download the file from our server OR it is done for security reasons to limit the number of sites which students can visited and help to reduce traffic to unwanted sites OR ... (for several other good reasons). If the file is delivered from a local cache (as opposed to from The Physics Classroom server), then the MOP log-in file knows that it is not coming from our school server and thus shuts down. If you hit the re-load page button (OR log off and back on OR go to another computer which has not done MOP in the last X days), then the browser doesn't pull the log-in file in from the local cache but goes out to our site to pull it in and the log-in file works because it recognizes that it was delivered from our site.Technical people at a school can often fix your problem by changing a browser or school server setting. You'll have to give them this info so that they know what is going on.
Teachers who are interested in using the Minds On Physics Internet Modules with their classes can read more about it on a separate page.
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