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{{Other uses|bow shock (aerodynamics)}} | |||
[[File:52706main hstorion lg.jpg|thumb|right|<center>[[LL Ori]] bow shock in [[Orion nebula]]. The star's wind collides with the nebula flow.<br>Hubble, 1995</center>]] | |||
<!-- new image needed [[ |thumb|350px|right|The locations of [[Voyager probes|Voyagers 1 and 2]] as of 2005. The "bow shock" shown is the shock caused by the sun as it moves through the [[interstellar medium]]; the Earth is too small to be seen on this scale. Note that the intensity of this shock is greatly exaggerated.]] --> | |||
In [[astrophysics]], a '''bow shock''' is the area between a [[magnetosphere]] and an ambient medium. For stars, this boundary is typically the edge of the [[astrosphere]], where the [[stellar wind]] meets the [[interstellar medium]]. For a planetary [[magnetosphere]], the bow shock is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the [[magnetopause]].<ref>{{cite journal|last1=Sparavigna|first1=A.C.|last2=Marazzato|first2=R.|title=Observing stellar bow shocks|date=10 May 2010|url=http://arxiv.org/ftp/arxiv/papers/1005/1005.1527.pdf|format=PDF}}</ref> The best-studied example of a bow shock is that occurring where the [[solar wind|Sun's wind]] encounters [[Earth]]'s magnetopause, although bow shocks occur around all magnetized planets, such as [[Jupiter#Magnetosphere|Jupiter]]<ref>{{cite journal|last1=Szego|first1=Karoly|title=Cassini plasma spectrometer measurements of Jovian bow shock structure|date=18 July 2003|url=http://eprints.ucl.ac.uk/81775/}}</ref> or [[Saturn#Magnetosphere|Saturn]].<ref>{{cite news|title=Cassini encounters Saturn's bow shock|date=|year=|month=|url=http://www-pw.physics.uiowa.edu/space-audio/cassini/bow-shock/|newspaper=Department of Physics and Astronomy, University of Iowa}}</ref> Earth's bow shock is about {{convert|17|km}} thick<ref>{{cite news|title=Cluster reveals Earth's bow shock is remarkably thin|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=49637|newspaper=European Space Agency|date=16 November 2011}}</ref> and located about {{convert|90,000|km}} from the planet.<ref>{{cite news|title=Cluster reveals the reformation of the Earth's bow shock|url=http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=40994|newspaper=European Space Agency|date=11 May 2011}}</ref> | |||
For several decades, the solar wind has been thought to form a bow shock at the edge of the [[heliosphere]], where it collides with the surrounding interstellar medium. This long-held belief was called into question in 2012 when data from the [[Interstellar Boundary Explorer]] (IBEX) found [[Sun|the Sun]] and heliosphere to be moving more slowly through the interstellar medium than previously believed.<ref name=bow>[http://www.nasa.gov/mission_pages/ibex/news/nobowshock.html NASA - IBEX Reveals a Missing Boundary At the Edge Of the Solar System]</ref> This new finding suggests that beyond our [[Solar System]]'s [[termination shock]] and [[Heliopause (astronomy)|heliopause]], there may be no, or very little bow shock.<ref name=bow/> | |||
==Description== | |||
The defining criterion is that the bulk velocity of the fluid (in this case, the [[Plasma (physics)|plasma]] of the solar wind) drops from "[[Supersonic speed|supersonic]]" to "subsonic", where [[plasma physics|the speed of sound in a plasma]] is defined as | |||
<math>c_s^2 = \gamma p/ \rho </math> | |||
where ''c<sub>s</sub>'' is the speed of sound, <math> \gamma </math> is the [[Heat capacity ratio|ratio of specific heats]], ''p'' is the [[pressure]], and <math> \rho </math> is the density of the plasma. | |||
The particles making up the solar wind follow spiral paths along magnetic field lines. The velocity of each particle as it gyrates around a field line can be treated similarly to a thermal velocity in an ordinary gas, and in an ordinary gas, the mean thermal velocity is roughly the speed of sound. At the bow shock, the bulk forward velocity of the wind (which is the component of the velocity parallel to the field lines about which the particles gyrate) drops below the speed at which the particles are corkscrewing. | |||
Bow shocks are also a common feature in [[Herbig Haro objects]], in which a much stronger collimated outflow of gas and dust from the star interacts with the interstellar medium, producing bright bow shocks that are visible at optical wavelengths. | |||
The following images show further evidence of bowshock existence from dense gases and plasma in the [[Orion Nebula]]. | |||
<gallery> | |||
Image:Heliosheath.JPG| | |||
Image:Heliosheath2.JPG| | |||
Image:Heliosheath3.JPG| | |||
Image:Heliosheath4.JPG| | |||
</gallery> | |||
==The Sun== | |||
It was hypothesised that the [[heliosphere]] also forms a bow shock as it travels through the [[interstellar medium]]. This will occur if the interstellar medium is moving supersonically ''towards'' the Sun, since the solar wind is moving supersonically ''away'' from the Sun. The point where the flow of the interstellar medium becomes subsonic is the bow shock; the point where the interstellar medium and solar wind pressures balance is at the [[heliopause (astronomy)|heliopause]]; the point where the solar wind flow becomes subsonic is the [[termination shock]]. According to [[Robert J. Nemiroff]] and Jerry Bonnell of [[NASA]], the solar bow shock would lie at a distance around 230 AU<ref>http://antwrp.gsfc.nasa.gov/apod/ap020624.html</ref> from the Sun - more than twice the distance of the termination shock as encountered by the Voyager spacecraft. However, data in 2012 from NASA's [[Interstellar Boundary Explorer]] (IBEX) and corroborated with results from the [[Voyager program|Voyager spacecraft]], has found that due to refinements in the relative speed of the heliosphere and the local interstellar magnetic field strength it is believed the heliosphere is prevented from forming a bow shock in the region of our galaxy the Sun is currently passing through. | |||
==In the infrared== | |||
In 2006, a far infrared bow shock was detected near the [[asymptotic giant branch|AGB star]] [[R Hydrae]].<ref>[http://cdsads.u-strasbg.fr/cgi-bin/nph-data_query?bibcode=2006ApJ...648L..39U&db_key=AST&link_type=ABSTRACT&high=45ba3a9f6d12619 Detection of a Far-Infrared Bow Shock Nebula around R Hya: The First MIRIAD Results]</ref>[[Image:Sig06-029 medium.jpg|thumb|350px|right|The bow shock around R Hydrae<ref>[http://sscws1.ipac.caltech.edu/Imagegallery/image.php?image_name=sig06-029 Spitzer Science Center Press Release: Red Giant Plunging Through Space]</ref>]] | |||
==See also== | |||
* [[Shock wave]] | |||
* [[Heliosheath]] | |||
* [[Fermi glow]] | |||
* [[List of plasma (physics) articles]] | |||
==Notes== | |||
{{reflist}} | |||
==References== | |||
*{{Cite book |last=Kivelson |first=M. G. |last2=Russell |first2=C. T. |year=1995 |title=Introduction to Space Physics |location=New York |publisher=Cambridge University Press |page=129 |isbn=0-521-45104-3 }} | |||
*{{Cite book |last=Cravens |first=T. E. |year=1997 |title=Physics of Solar System Plasmas |location=New York |publisher=Cambridge University Press |page=142 |isbn=0-521-35280-0 }} | |||
==External links== | |||
*[http://antwrp.gsfc.nasa.gov/apod/image/0011/bzcam_wiyn.gif Bow shock image (BZ Cam)] | |||
*[http://antwrp.gsfc.nasa.gov/apod/image/0010/gcenter2_gemini_big.jpg Bow shock image (IRS8)] | |||
*[http://www.eso.org/public/archives/images/screen/eso9702a.jpg Bow shock image (HD77581)] | |||
*[http://imgsrc.hubblesite.org/hu/db/2002/05/images/a/formats/large_web.jpg Bow shock image (LL Ori)] | |||
*[http://www.atnf.csiro.au/pasa/17_1/cairns/paper/node1.html#fig3 Good diagram from a research paper on shocks] | |||
*[http://www.dartmouth.edu/~hrm/R/heliosphere.html More on the ''Voyagers''] | |||
*[http://www-pw.physics.uiowa.edu/space-audio/sounds/jovbow.wav Hear Jovian bow shock from the Uni. of Iowa] | |||
*[http://www.physorg.com/news98367923.html Cluster spacecraft makes a shocking discovery (Planetary Bow Shock)] | |||
{{The Sun}} | |||
[[Category:Planetary science]] | |||
[[Category:Sun]] | |||
[[Category:Shock waves]] | |||
[[Category:Waves in plasmas]] | |||
Revision as of 12:47, 22 January 2014
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Hubble, 1995
In astrophysics, a bow shock is the area between a magnetosphere and an ambient medium. For stars, this boundary is typically the edge of the astrosphere, where the stellar wind meets the interstellar medium. For a planetary magnetosphere, the bow shock is the boundary at which the speed of the stellar wind abruptly drops as a result of its approach to the magnetopause.[1] The best-studied example of a bow shock is that occurring where the Sun's wind encounters Earth's magnetopause, although bow shocks occur around all magnetized planets, such as Jupiter[2] or Saturn.[3] Earth's bow shock is about Template:Convert thick[4] and located about Template:Convert from the planet.[5]
For several decades, the solar wind has been thought to form a bow shock at the edge of the heliosphere, where it collides with the surrounding interstellar medium. This long-held belief was called into question in 2012 when data from the Interstellar Boundary Explorer (IBEX) found the Sun and heliosphere to be moving more slowly through the interstellar medium than previously believed.[6] This new finding suggests that beyond our Solar System's termination shock and heliopause, there may be no, or very little bow shock.[6]
Description
The defining criterion is that the bulk velocity of the fluid (in this case, the plasma of the solar wind) drops from "supersonic" to "subsonic", where the speed of sound in a plasma is defined as
where cs is the speed of sound, is the ratio of specific heats, p is the pressure, and is the density of the plasma.
The particles making up the solar wind follow spiral paths along magnetic field lines. The velocity of each particle as it gyrates around a field line can be treated similarly to a thermal velocity in an ordinary gas, and in an ordinary gas, the mean thermal velocity is roughly the speed of sound. At the bow shock, the bulk forward velocity of the wind (which is the component of the velocity parallel to the field lines about which the particles gyrate) drops below the speed at which the particles are corkscrewing.
Bow shocks are also a common feature in Herbig Haro objects, in which a much stronger collimated outflow of gas and dust from the star interacts with the interstellar medium, producing bright bow shocks that are visible at optical wavelengths.
The following images show further evidence of bowshock existence from dense gases and plasma in the Orion Nebula.
The Sun
It was hypothesised that the heliosphere also forms a bow shock as it travels through the interstellar medium. This will occur if the interstellar medium is moving supersonically towards the Sun, since the solar wind is moving supersonically away from the Sun. The point where the flow of the interstellar medium becomes subsonic is the bow shock; the point where the interstellar medium and solar wind pressures balance is at the heliopause; the point where the solar wind flow becomes subsonic is the termination shock. According to Robert J. Nemiroff and Jerry Bonnell of NASA, the solar bow shock would lie at a distance around 230 AU[7] from the Sun - more than twice the distance of the termination shock as encountered by the Voyager spacecraft. However, data in 2012 from NASA's Interstellar Boundary Explorer (IBEX) and corroborated with results from the Voyager spacecraft, has found that due to refinements in the relative speed of the heliosphere and the local interstellar magnetic field strength it is believed the heliosphere is prevented from forming a bow shock in the region of our galaxy the Sun is currently passing through.
In the infrared
In 2006, a far infrared bow shock was detected near the AGB star R Hydrae.[8]
See also
Notes
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References
- 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534 - 20 year-old Real Estate Agent Rusty from Saint-Paul, has hobbies and interests which includes monopoly, property developers in singapore and poker. Will soon undertake a contiki trip that may include going to the Lower Valley of the Omo.
My blog: http://www.primaboinca.com/view_profile.php?userid=5889534
External links
- Bow shock image (BZ Cam)
- Bow shock image (IRS8)
- Bow shock image (HD77581)
- Bow shock image (LL Ori)
- Good diagram from a research paper on shocks
- More on the Voyagers
- Hear Jovian bow shock from the Uni. of Iowa
- Cluster spacecraft makes a shocking discovery (Planetary Bow Shock)
- ↑ One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting
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Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ One of the biggest reasons investing in a Singapore new launch is an effective things is as a result of it is doable to be lent massive quantities of money at very low interest rates that you should utilize to purchase it. Then, if property values continue to go up, then you'll get a really high return on funding (ROI). Simply make sure you purchase one of the higher properties, reminiscent of the ones at Fernvale the Riverbank or any Singapore landed property Get Earnings by means of Renting
In its statement, the singapore property listing - website link, government claimed that the majority citizens buying their first residence won't be hurt by the new measures. Some concessions can even be prolonged to chose teams of consumers, similar to married couples with a minimum of one Singaporean partner who are purchasing their second property so long as they intend to promote their first residential property. Lower the LTV limit on housing loans granted by monetary establishments regulated by MAS from 70% to 60% for property purchasers who are individuals with a number of outstanding housing loans on the time of the brand new housing purchase. Singapore Property Measures - 30 August 2010 The most popular seek for the number of bedrooms in Singapore is 4, followed by 2 and three. Lush Acres EC @ Sengkang
Discover out more about real estate funding in the area, together with info on international funding incentives and property possession. Many Singaporeans have been investing in property across the causeway in recent years, attracted by comparatively low prices. However, those who need to exit their investments quickly are likely to face significant challenges when trying to sell their property – and could finally be stuck with a property they can't sell. Career improvement programmes, in-house valuation, auctions and administrative help, venture advertising and marketing, skilled talks and traisning are continuously planned for the sales associates to help them obtain better outcomes for his or her shoppers while at Knight Frank Singapore. No change Present Rules
Extending the tax exemption would help. The exemption, which may be as a lot as $2 million per family, covers individuals who negotiate a principal reduction on their existing mortgage, sell their house short (i.e., for lower than the excellent loans), or take part in a foreclosure course of. An extension of theexemption would seem like a common-sense means to assist stabilize the housing market, but the political turmoil around the fiscal-cliff negotiations means widespread sense could not win out. Home Minority Chief Nancy Pelosi (D-Calif.) believes that the mortgage relief provision will be on the table during the grand-cut price talks, in response to communications director Nadeam Elshami. Buying or promoting of blue mild bulbs is unlawful.
A vendor's stamp duty has been launched on industrial property for the primary time, at rates ranging from 5 per cent to 15 per cent. The Authorities might be trying to reassure the market that they aren't in opposition to foreigners and PRs investing in Singapore's property market. They imposed these measures because of extenuating components available in the market." The sale of new dual-key EC models will even be restricted to multi-generational households only. The models have two separate entrances, permitting grandparents, for example, to dwell separately. The vendor's stamp obligation takes effect right this moment and applies to industrial property and plots which might be offered inside three years of the date of buy. JLL named Best Performing Property Brand for second year running
The data offered is for normal info purposes only and isn't supposed to be personalised investment or monetary advice. Motley Fool Singapore contributor Stanley Lim would not personal shares in any corporations talked about. Singapore private home costs increased by 1.eight% within the fourth quarter of 2012, up from 0.6% within the earlier quarter. Resale prices of government-built HDB residences which are usually bought by Singaporeans, elevated by 2.5%, quarter on quarter, the quickest acquire in five quarters. And industrial property, prices are actually double the levels of three years ago. No withholding tax in the event you sell your property. All your local information regarding vital HDB policies, condominium launches, land growth, commercial property and more
There are various methods to go about discovering the precise property. Some local newspapers (together with the Straits Instances ) have categorised property sections and many local property brokers have websites. Now there are some specifics to consider when buying a 'new launch' rental. Intended use of the unit Every sale begins with 10 p.c low cost for finish of season sale; changes to 20 % discount storewide; follows by additional reduction of fiftyand ends with last discount of 70 % or extra. Typically there is even a warehouse sale or transferring out sale with huge mark-down of costs for stock clearance. Deborah Regulation from Expat Realtor shares her property market update, plus prime rental residences and houses at the moment available to lease Esparina EC @ Sengkang - ↑ Template:Cite news
- ↑ Template:Cite news
- ↑ Template:Cite news
- ↑ 6.0 6.1 NASA - IBEX Reveals a Missing Boundary At the Edge Of the Solar System
- ↑ http://antwrp.gsfc.nasa.gov/apod/ap020624.html
- ↑ Detection of a Far-Infrared Bow Shock Nebula around R Hya: The First MIRIAD Results
- ↑ Spitzer Science Center Press Release: Red Giant Plunging Through Space