Tuesday, August 18, 2009

Perseids History

The earliest record of Perseid activity comes from the Chinese annals, where it is said that in 36 AD "more than 100 meteors flew thither in the morning." Numerous references appear in Chinese, Japanese and Korean records throughout the 8th, 9th, 10th and 11th centuries, but only sporadic references are found between the 12th and 19th centuries, inclusive. Nevertheless, August has long had a reputation for an abundance of meteors. The Perseids have been referred to as the "tears of St. Lawrence", since meteors seemed to be in abundance during the festival of that saint in Italy on August 10th; however, credit for the discovery of the shower's annual appearance is given to Adolphe Quételet (Brussels, Belgium), who, in 1835, reported that there was a shower occurring in August that emanated from the constellation Perseus.

The first observer to provide an hourly count for this shower was E. Heis (Münster), who found a maximum rate of 160 meteors per hour in 1839. Observations by Heis and other observers around the world continued almost annually thereafter, with maximum rates typically falling between 37 and 88 per hour through 1858. Interestingly, the rates jumped to between 78 and 102 in 1861, according to estimates by four different observers, and, in 1863, three observers reported rates of 109 to 215 per hour. Although rates were still somewhat high in 1864, generally "normal" rates persisted throughout the remainder of the 19th-century.

Computations of the orbit of the Perseids between 1864 and 1866 by G. V. Schiaparelli (Italy) revealed a very strong resemblance to periodic comet 109P/Swift-Tuttle, which had been discovered in 1862. This was the first time a meteor shower had been positively identified with a comet and it seems safe to speculate that the high Perseid rates of 1861-1863 were directly due to the appearance of 109P/Swift-Tuttle, which has a period of about 135 years. Multiple returns of the comet would be responsible for the distribution of the meteors throughout the orbit, but meteors should be denser in the region closest to the comet, so that meteor activity should increase when the comet is near perihelion.

During 1973, the astronomer Brian G. Marsden examined the orbit of periodic comet 109P/Swift-Tuttle to determine when it was likely to return. The observations from the 1862 return were not the best and the uncertainty in the orbital period amounted to several years. His best bet was to try and identify a previous return. He found two good options: a comet in 1737 and one in 1750. Marsden chose the 1750 comet as the best candidate for a previous appearance of comet 109P/Swift-Tuttle and predicted the comet would return in 1981. This immediately generated excitement among meteor observers as the potential for enhanced activity unfolded. This excitement seems to have been fully justified, as the average rate of 65 per hour during 1966-1975 suddenly jumped to over 90 per hour during 1976-1983---with the high being 187 in the latter year. Although meteor observers seemed content with their observations of the enhanced activity from 109P/Swift-Tuttle, comet observers were less enthusiastic as the comet was not recovered. Following the 1983 peak, hourly rates for the Perseids declined. With a full moon occurring just a day before maximum in 1984, the Dutch Meteor Society still reported unexpectedly high rates of 60 meteors per hour. In 1985, reported rates generally fell between 40 and 60 meteors per hour in dark skies, and results were generally the same in 1986.


As the 1990s dawned, Marsden published a new prediction. If comet 109P/Swift-Tuttle was actually seen in 1737, then the comet might pass perihelion during December 1992. The comet was recovered late in the summer of 1992. Although not one of the most spectacular apparitions, the comet was well observed. But meteor observers were more interested in the Perseid display of 1993. Predictions indicated Europe was the place to be during August of 1993. Observers from around the world flocked into central Europe and were met with hourly rates of 200 to 500! High rates were still present during 1994, this time with the peak occurring over the United States.

The Perseid radiant turns out to be complex. The main radiant is situated near the star Eta Persei, but other radiants appear to be active at the same time. As long ago as 1879, W. F. Denning (England) pointed out that he had "detected the existence of two other simultaneous showers from Chi and Gamma Persei." This latter shower is one of the most active of the secondary radiants and seems to have been frequently observed during the twentieth century---especially with telescopic aid. One of the most recent examples of the complexity of the Perseid meteor shower was revealed in three studies of the radiant conducted during 1969 to 1971, by observers in the Crimea. In addition to the main radiant near Eta Persei, they confirmed the existence of the major radiants near Chi and Gamma Persei, as well as minor radiants near Alpha and Beta Persei. These meteor showers are generally short-lived and exhibit radiants that move nearly parallel to the main radiant.

There is an uneven size distribution within the stream. One very interesting characteristic of the Perseids is that there are times when larger, brighter meteors are much more plentiful than smaller, fainter meteors. In 1953, A. Hruska (Czechoslovakia) found that Perseids were brighter during August 8-12, slightly fainter on August 12/13, and notably fainter by August 14/15. In 1956, Z. Cephecha (Czechoslovakia) found the meteors were brightest on the night of Augsut 6/7 and faintest on the night of August 13/14. A similar pattern has been noted by more recent studies during the 1980s and 1990s. All of the magnitude studies have one thing in common---they point to an irregular mass distribution within the Perseid stream. Some of this is most likely due to the Earth encountering filaments of material representing different that comet Swift-Tuttle has moved in during the last 2000 years.

There is an odd variation from year to year in the number of Perseids exhibiting persistent trains. One of the first astronomers to study this was M. Plavec (Czechoslovakia), who examined 8028 Perseids seen during the period spanning 1933 to 1947. He noted the 45% of Perseids exhibited persistent trains in 1933, while this was value changed to 60% in 1936, 35% in 1945, and 53.3% in 1947. Plavec noted that he could not correlate the variations to sunspot numbers. It could be that this is also tied in to Earth encountering different orbital filaments perviously shed by comet Swift-Tuttle.

Location of the Perseids For Southern Hemisphere Observers

Location of the Perseids For Northern Hemisphere Observers

Perseids

This is the most famous of all meteor showers. It never fails to provide an impressive display and, due to its summertime appearance, it tends to provide the majority of meteors seen by non-astronomy enthusiasts.

This meteor shower gets the name "Perseids" because it appears to radiate from the constellation Perseus. An observer in the Northern Hemisphere can start seeing Perseid meteors as early as July 23, when one meteor every hour or so could be visible. During the next three weeks, there is a slow build-up. It is possible to spot five Perseids per hour at the beginning of August and perhaps 15 per hour by August 10. The Perseids rapidly increase to a peak of 50-80 meteors per hour by the night of August 12/13 and then rapidly decline to about 10 per hour by August 15. The last night meteors are likely to be seen from this meteor shower is August 22, when an observer might see a Perseid every hour or so.

For observers in the Southern Hemisphere, the Perseid radiant never climbs above the horizon, which will considerably reduce the number of Perseid meteors you are likely to see. Nevertheless, on the night of maximum, it is possible to see 10-15 meteors per hour coming up from the northern horizon.

There are other, weaker meteor showers going on around the same time as the Perseids, but the Perseids will generally appear to move much faster across the sky than meteors from the other showers. In fact, the Perseids are among the fastest moving meteors we see every year. Another way to know if the meteor you saw was a Perseid is to mentally trace the meteor backwards. If you end up at Perseus then you have probably seen a Perseid meteor! If you are not sure where Perseus is in the sky, the following charts will help you find it from both the Northern Hemisphere and Southern Hemisphere:

Indexing

XP Tips & Tweaks - Turn Off Indexing to Speed Up XP


Windows XP keeps a record of all files on the hard disk so when you do a search on the
hard drive it is faster. There is a downside to this and because the computer has to index
all files, it will slow down normal file commands like open, close, etc. If you do not do a
whole lot of searches on your hard drive then you may want to turn this feature off:
• Open My Computer.
• Right-click your hard drive icon and select Properties.
• At the bottom of the window you'll see "Allow indexing service to index this disk
for faster searches," uncheck this and click ok.
• A new window will pop up and select Apply to all folders and subfolders.
It will take a minute or two for the changes to take affect but then you should enjoy
slightly faster performance.

Slow Network

If you have very slow access to your network computers through "My Network Places"
and have already deleted the Registry entry calling for a check of Scheduled Tasks on the
other network computers (documented elsewhere on this site) AND you have multiple
network adaptors (i.e. a cable or DSL connection through one NIC and an internal network
using a second NIC) check the following:
• Right-click on "My Network Places", go to Properties.
• Right-click on the NIC that your cable/DSL connects to, and choose Properties.
• Select Internet Protocol (TCP/IP), and click on Properties.
• Click on "Advanced", go to "WINS" tab, and chose Disable NetBios over TCP/IP.
• When you are back at your Network Connections page, right-click on the
Broadband selection.
• Choose "Properties", click on the Networking tab.
• Again, choose TCP/IP, Properties, Advanced, WINS, and select "disable NetBios
over TCP/IP".

Disable Boot screen

XP Tips & Tweaks - Disable XP Boot Logo


It is possible to disable the XP splash screen, which will slightly speed up the overall boot
process. Be aware that removing the splash screen will also cause you not to see any
boot-up messages that might come up (chkdsk, convert ... ), but if your system runs
without any problems then it should not matter.
• Edit boot.ini.
• Add " /noguiboot" right after "/fastdetect".
Upon restarting, the splash screen will be gone. It can be re-enabled by removing the new
switch.

Correcting System


XP Tips & Tweaks - Correcting System Hang at Startup

If your system hangs about 2 or 3 minutes at startup, where you can't access the Start
button or the Taskbar, it may be due to one specific service (Background Intelligent
Transfer) running in the background. Microsoft put out a patch for this but it didn't work
for me. Here's what you do:


• Click on Start/Run, type 'msconfig', then click 'OK'.
• Go to the 'Services' tab, find the 'Background Intelligent Transfer' service.
• Disable it, apply the changes & reboot.

Startup Slow

XP Tips & Tweaks - Slow Start-up When Using Norton Internet Security 2002

If you are using Norton Internet Security 2002, and are experiencing slow start-up of XP,
(i.e. you can see the desktop with icons etc. but it takes 30-60sec before you can start
using the computer), this fix might help:
• Click on Start button.
• Select Control Panel.
• Open "Network Connections".
• Under "LAN and High-Speed Internet", right-click on your "Local Area Connection"
and select "Properties".
• Under "General" tab, select "Internet Protocol (TCP/IP)" and select "Properties".
• Select "Use the following IP address:".
• Under "IP address" enter following : 192.168.0.1
• Under "Subnet Mask:" enter following : 255.255.255.0
• Click "Ok".

Adjust System Cache

XP Tips & Tweaks - Easy Way to Adjust LargeSystemCache

Normally, the tweak I've seen asks you to go into
HKLM\System\CurrentControlSet\Control\Session Manager\Memory Management and
change the value to either O or 1 to the adjustment the LargeSystemCache.
However, in Windows XP, all you have to do is:
• Right-click My Computer.
• Select Properties.
• Click Advanced.
• Choose Performance.
• Click Advanced again.
• Select either Programs or System Cache under Memory Usage.
Programs = 0 for the registry tweak equivalent
System Cache = 1 for the registry tweak equivalent
• On NT Server (in this case XP), the Large System Cache option is enabled, but
disabled on Workstation. The two different settings effect how the cache manager
allocates free memory. If the Large Cache option is on, the manager marks all the
free memory, which isn't being used by the system and/or applications, as freely
available for disk caching.
• On the flip-side (with a small cache), the manager instead only sets aside 4MB of
memory for disk caching in an attempt to accelerate the launch of applications. Or
in a more technical approach, if enabled the system will favor system-cache
working sets over process working sets (with a working set basically being the
memory used by components of a process).

System Restore

XP Tips & Tweaks - Turn Off System Restore to Save Space

By default, Windows XP keeps a backup of system files in the System Volume Information
folder. This can eat up valuable space on your hard drive. If you don't want Windows to
back up your system files:
• Open the Control Panel.
• Double-click on System.
• Click the System Restore tab.
• Check "Turn off System Restore on all drives".
• Hit Apply.
• You may now delete the System Volume Information folder.


Warning! If you turn this off you will not be able to use Windows System Restore to
restore your system in case of failure.

Very Slow Boot

XP Tips & Tweaks - Very Slow Boot When Networking

On some XP Pro installations, when connected to a network (peer-peer in this case), the computer boot time is over 1:40. The system seems to freeze after logging in and the desktop may not appear or will freeze for a minute. As timed with the utility, Bootvis.exe, the problem was with the driver mrxsmb.dll, adding over 67 seconds to the boot time.

Turning off and restoring file and printer sharing eliminated 65 seconds from the boot
time.
• Alt-click (or right-click) on Network Places > Properties.
• Alt-click on Ethernet Adapter connection > Properties.
• Un-check "File and Printer Sharing for Microsoft Networks" > OK.
• Reboot.
• If you need file or printer sharing, repeat the above, re-check the box and re-boot
again.

Speed Up Explorer


XP Tips & Tweaks - Speed Up Detailed View in Explorer

If you like to view your files in Windows Explorer using the "Details" view here is a tweak to speed up the listing of file attributes: Viewing files in Windows Explorer using the "Details" mode shows various attributes associated with each file shown. Some of these must be retrieved from the individual files when you click on the directory for viewing. For a directory with numerous and relatively large files (such as a folder in which one stores media, eg: *.mp3's, *.avi's etc.), Windows Explorer lags as it reads through each one. Here's how to disable viewing of unwanted attributes and speed up file browsing:


• Open Windows Explorer.
• Navigate to the folder which you wish to optimize.
• In "Details" mode right-click the bar at the top which displays the names of the attribute columns.
• Uncheck any that are unwanted/unneeded. Explorer will apply your preferences immediately, and longs lists of unnecessary attributes will not be displayed.
Likewise, one may choose to display any information which is regarded as needed, getting
more out of Explorer.


Easily Disable Messenger
Go into: C:/Program Files/Messenger. Rename the Messenger folder to "MessengerOFF".
This does not slow down Outlook Express or hinder system performance.
Turn

Speeding computer

XP Tips & Tweaks - Speeding Up Your Pentium 2 by 50%


We all know that you really shouldn't try to run Windows XP on anything less that about a Pentium 3 of some sort if you are out for speedy operations and amazing reaction times, but for those of us with the good old Pentium 2's who want to see just how well we can run XP, we have to tweak as much as we can where-ever we can. A real killer to the system's performance is Windows Media Player. Although it may look desirable and fancy with it's rounded off edges and 3rd-Dimensional appearance, the truth is, it takes up a large amount of that precious processing power. All of these troubles however, lead to one thing in particular with this 'new-look' over-rated music and video player...the Visualizations. The look-great I'll admit but like a lot of software these days, it has no purpose. If you run the task manager, and click the Performance tab along the top, you'll see that when Windows Media Player is running and nothing else is active, it takes up around 50% of the processors power. Once these visualizations are turned off, it barely takes up 2-3% of the processors power, which leaves much more room for other applications to work efficiently.


Here's how to disable the feature:
• Open Media Player.
• Make sure the Now Playing tab on the left is selected.
• Click the View menu along the top.
• Go down to Now Playing Tools.
• In the sub-menu that has just 'popped-out', uncheck Show Visualization.

Tag

Assignment Lanka Tag Cloud
Computer Networks The History of Local Area Networks, LAN, The Topologies of a Networks, LANs describe different types of transmission Medias, Local Area Networks Access Methods, Carrier Sense Multiple Access with Collision Detect, Development of LAN Technologies. LAN -Token Ring, LAN Ethernet Digital, LAN - Ethernet Sun microsystems, LAN - Ethernet Mixed Environment, LAN - Token Ring was introduced by IBM LAN - IBM implementation of Token Ring, Token Ring Novell, LAN Token Ring - in a mixed environment, LAN - Fiber Distributed Data Interface, LAN - ATM, LAN Components, LAN Switching Methods, Virtual Local Area Network, Port based VLAN, Mac based VLAN, Protocol based VLAN, User Base VLAN, PC networks Components, PC networks Shared resources, PC Network operating systems, PC networks Novell Netware, PC networks Windows NT, PC networks IBM LAN Server Computer Programming Languages HTML Language, The Generations of Programming Languages, Different types of High Level Languages, Different types of High Level Languages Disadvantages
Computer Networks - IBM LAN Server, Windows NT Networks, Novell Netware, Network operating systems, Networks Shared, Networks Components, User Base, Protocol based, Mac based, Port based, VLAN, LAN Switching, LAN Components, ATM, Fiber Data, Token Ring, Token Ring Novell, IBM implementation, Ethernet, Sun microsystems, Ethernet Digital, Token passing, LAN Technologies, CSMA/CD, Access Methods, Transmission, Networks, The History of Local Area Networks, LAN