Refraction, sunrise, sunset
>> Monday, February 22, 2010
Due to refraction :
- The sun will appear to rise sooner (by approximately two minutes) than it actually does
- The sun will appear to set a bit later (by about two minutes) than it actually does
>> Thursday, February 4, 2010
Lightning may not seem much like static electricity, but it's actually very similar. Both are sparks of electricity created through the attraction of unlike charges. The difference is that static electricity
creates a small spark, while lightning is a huge spark of electricity.In storm clouds, tiny particles in the cloud move around picking up positive or negative energy charges, like when shoes scuff a rug. The positive charged particles stay light, and rise to the top of the cloud. The negative charged particles get heavier, and collect at the bottom of the cloud.
As more particles become charged, they divide into opposing groups in the cloud. When the power of attraction between them gets too great, the particles discharge their energy at each other, completing a path for electricity to travel through the air. We call this flow of electricity lightning.
It's the negative charges in the bottom of the cloud that cause lightning to strike the ground. When the negatively charged particles group together, they begin to seek out positive charges from the ground below. The excess electrons create a channel of charged air called a leader that reaches down to the ground below. The leaders attract other charged ground-based channels called streamers.
When the stepped leader from the cloud meets a returning streamer from the ground, the path is ready. An electrical current called the return stroke, travels back up the path. This return stroke releases tremendous energy, bright light and thunder.
The typical stroke can last only 30 milliseconds, so four to five strokes may happen in the blink of an eye. Despite the old saying, lightning does strike the same place twice.
To review, lightning is created by the attraction between opposite charges, the same force that creates static electricity. But lightning uses huge opposite charges to produce an electrical current that's nothing like what you'd get from static electricity.
>> Friday, January 29, 2010
Stars
On a clear dark night, a few thousand stars are visible to the naked eye. With
binoculars and powerful telescopes, we can see so many stars that we could never hope to count them. Even though each individual star is unique, all stars share much in common. The Sun, which is the source of virtually all light, heat and energy reaching the Earth, is the nearest star. Today, we know that stars are born from interstellar gas clouds, shine by nuclear fusion and then die, sometimes in dramatic ways.
Globular Cluster M3.
Some 500,000 stars are
crammed into an region about
100 light years across in
this globular cluster
Why do stars twinkle?
The songline goes "Twinkle twinkle little star". What is the cause of the "twinkling" of stars? Does light from planets "twinkle" as does light from stars?
Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle." This is one of the reasons the Hubble telescope is so successful: in space, there is no atmosphere to make the stars twinkle, allowing a much better image to be obtained.
Planets do not twinkle the way stars do. In fact, this is a good way of figuring out if a particular object you see in the sky is a planet or a star. The reason is that stars are so far away that they are essentially points of light on the sky, while planets actually have finite size. The size of a planet on the sky in a sense "averages out" the turbulent effects of the atmosphere, presenting a relatively stable image to the eye.
Read more...
The songline goes "Twinkle twinkle little star". What is the cause of the "twinkling" of stars? Does light from planets "twinkle" as does light from stars?
Stars twinkle because of turbulence in the atmosphere of the Earth. As the atmosphere churns, the light from the star is refracted in different directions. This causes the star's image to change slightly in brightness and position, hence "twinkle." This is one of the reasons the Hubble telescope is so successful: in space, there is no atmosphere to make the stars twinkle, allowing a much better image to be obtained.
Planets do not twinkle the way stars do. In fact, this is a good way of figuring out if a particular object you see in the sky is a planet or a star. The reason is that stars are so far away that they are essentially points of light on the sky, while planets actually have finite size. The size of a planet on the sky in a sense "averages out" the turbulent effects of the atmosphere, presenting a relatively stable image to the eye.
Salam Aidilfitri
>> Wednesday, September 16, 2009
Guru-guru daripada panitia fizik ingin mengucapkan selamat menyambut Hari Raya Aidilfitri kepada semua warga sekolah termasuklah guru-guru, staf sokongan dan pelajar-pelajar. Maaf zahir dan Batin.
Read more...
Subscribe to:
Posts (Atom)
