By Sten Odenwald
How briskly does gravity shuttle? while will the solar cross nova? Who invented the sunshine 12 months? can we ever trip to the celebs? those are only a few of the strange and renowned questions NASA astronomer Sten Odenwald solutions in again to the Astronomy Caf?, in response to his award-winning web site "for the astronomically disadvantaged." because his acclaimed past booklet The Astronomy Caf? released in 1998, the distance neighborhood has been became on its head with totally new discoveries: ion propulsion, darkish subject, gravity and magnetic reversals, the Cosmic darkish a while, and over a hundred new planets. within the all-new again to the Astronomy Caf?, Odenwald solutions the most recent and most-asked questions when it comes to those fresh discoveries. His hugely own and authoritative sort makes figuring out the cosmos much less intimidating, interesting, and fun.Since he opened his site "The Astronomy Caf?" in 1995, Odenwald has replied over 50,000 e-mailed questions. His person solutions were downloaded over 7.5 million occasions, making him the main sought-after "answer guy" for astronomy in human heritage.
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"Stellar Physics" is a a great e-book within the starting to be physique of literature on celebrity formation and evolution. not just does the writer, a number one specialist within the box, very completely current the present kingdom of information on stellar physics, yet he handles with equivalent care the various difficulties that this box of study nonetheless faces.
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Even if transits of planets around the sunlight are infrequent (only Mercury and Venus orbit the sunlight nearer than us, and so can transit the Sun's disc) beginner astronomers can notice, checklist and snapshot different kinds of transit, that are greatly extra widespread. Transit is in components, the 1st telling the interesting tale of the early medical expeditions to monitor transits.
Committee for an review of Precision Time and Time period technological know-how and know-how, nationwide study Council, department on Engineering and actual Sciences, Naval stories Board
Knowledge of time is key to express wisdom of place, and consequently the military, with its have to navigate at the excessive seas, has traditionally performed a massive position within the improvement and alertness of complex time cognizance and dissemination applied sciences. Discoveries coming from uncomplicated examine funded via the workplace of Naval examine (ONR) lie on the middle of state-of-the-art maximum functionality atomic clocks, Naval learn Laboratory (NRL) services performed a task in constructing the space-qualified atomic clocks that let the worldwide Positioning procedure (GPS), and the U. S. Naval Observatory (USNO) keeps and disseminates the normal of time for the entire division of protection (DOD). The military has made significant investments in such a lot points of precision time and time period (PTTI) technology and expertise, even if particular PTTI-related learn has additionally been funded by way of the safeguard complicated learn initiatives service provider (DARPA) and non-DOD enterprises comparable to the nationwide technological know-how origin (NSF), the nationwide Aeronautics and area management (NASA), and the dept of trade. military investment, principally via ONR, has a background of being an early enabler of key new advancements. really appropriate investment judgements through the Navy-particularly by means of ONR software officers-have underpinned many of the significant advances in PTTI technological know-how and know-how (S&T) within the final 50 years. PTTI is necessary to trendy naval wishes, and certainly to the entire armed prone, to be used in either navigation and communications. designated time synchronization is required to successfully make sure the beginning of a code series in safe communications, to accomplish navigation, and to find the placement of sign emitters. particular frequency regulate is needed in communications for spectrum usage and frequency-hopped spread-spectrum thoughts. there are numerous examples of crucial army operations that depend upon PTTI and will take advantage of advancements in PTTI expertise. those comprise: -GPS clocks and self reliant operations, -Weapon process 4-dimensional coordination, -GPS antijamming, -Network-centric war, and -Secure army communications. This record summarizes that discount rates within the measurement, weight, and gear necessities and raises within the ruggedness of PTTI units with no sacrificing functionality might placed extra actual and distinctive timekeeping within the fingers of the warrior, bettering functions in the entire above operations.
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The length of day or LOD is monitored by using trans-Atlantic Very Long Base Line Interferometry, a technique pioneered and still used by astronomers to study distant quasars. During the 1982-1983 El Nino, an even stronger LOD increase of 800 microseconds was detected, with a milder LOD increase detected a year later of about 400 microseconds. To understand how air currents can affect Earth's rotation, you have to consider an ice skater on the ice doing a spin. If she changes how far out she holds her hands by just a little, the rapidity of her spin is affected.
General relativity says that the universe is a four-dimensional object and that gravity can only be described in its full four-dimensional terms. This is hard for us to do because we keep wanting to think of things happening in space at separate times. We insist on slicing gravity's field one time step at a time. At each time step, the volume of space increases, but in some sense, this space, like the pulp of the watermelon, has always been there. In each slice, the space does not "come" from anywhere, it is just revealed to us a moment at a time like the pulp in the slices of the watermelon.
In 2002, a team of scientists at Harvard University made an even more exciting, and controversial, discovery. Adam Dziewonski and graduate student Miaki Ishii studied 325,000 seismic waves that had passed directly through the center of Earth in the last 30 years. About 3,000 of these seismic events show a pronounced change as they penetrate even closer to the center. Their best model accounting for the velocity changes within the inner core is that there is a separate, 360-mile diameter, mini-planet in its center.
Back to Astronomy Cafe by Sten Odenwald