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NATURE
Hi Friends ...

Here we may ask Questions related to Science, Arts, History, Culture, Natural Phenomena and all ...
Just to start with something... Will Any 1 please answer this ???
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How some Animals like Dogs, Cats can see in the Dark ? How can we see some Object ?
Now r u happy Mr. Yaar Mere Ji ? Tell me what makes them able to see in the dark ...
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U may continue this by asking Questions that create a kind of sensation in your mind .....
YaarMere
QUOTE(NATURE @ Sep 22 2005, 12:21 AM) *

It is the Light That comes from the Object to our Eye. Then how could they see ? ..
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I thought that you were well read on physics? Or are you just pretending in that other thread? Or is it that you just want a topic of your own?
NATURE
It became necessary to reply ... neither the former nor the later ( From yr 2 options )
U could take it as a Fun or Joke as "Well read Physics may write silly things" ... Never Mind , ok ?
Now tell me how can they see ? some animals and not all, what's the difference ???
visuja
Nature, I guess these animals would have more senstive 'rods' and 'cones' in their eyes, which are more adept at picking up light of lower intensity than humans can. Hence, what appears as darkness to us isnt probably really dark. Im sure these animals too wont be able to see anything in absolutely pitch black darkness.

What we see in the cats' eyes is probably the light relected off their lenses / vitreous humor (I assume). Nearly blind animals, like bats, obviously depend on other forms of 'sight' (echo location in this case) to 'see'.
YaarMere
QUOTE(NATURE @ Sep 22 2005, 03:00 AM) *

It became necessary to reply ... neither the former nor the later ( From yr 2 options )



I noticed you missed out option 3.
NATURE
Oph ho ... aap to bahut sayaanaa ho. Aur haa pakaate bhi ho sunglasses2.gif ... I missed all the options. But yeah,
I would like to choose yr 3rd option ... but that is partially true, I wanted a Topic of Sawaal - Jawaab
( Questioning - Answering )
But not by my own ... Is that not clear ??? I think u don't want to come to the Point .... Better delete this Topic ...
Can u do that ?
AzgarKhan
How do animals see in the dark?

IPB Image

After the emergence of vertebrates from the water some 300 million years ago, the evolving landscape became more and more crowded with large herbivores and predators. However, a rich ecological niche remained available to competitors with the right adaptations — the abilities to find food and avoid predators at night. Although mammals first evolved over 200 million years ago, the majority of them remained primarily nocturnal until the demise of their major predators, the dinosaurs about 65 million years ago. After that, new ecological niches became available in the light of day. Then the modern complement of both diurnal and nocturnal mammals evolved.

In order to survive at night, these animals had to find food in the dark. Some developed a highly-advanced senses of smell or specialized hearing abilities such as echolocation. Others acquired eye adaptations for improved night vision


Big Eyes

The most notable feature of nocturnal animals is the size of their eyes. Large eyes, with a wider pupil, larger lens and increased retinal surface can collect more ambient light. For example, an owl's eyes fill over one half its skull. Likewise, some species have evolved tubular eyes as a means of increasing their size. By expanding the eyes in this way, they are very tightly fit in the socket. As such, many nocturnal animals cannot move their eyes within the orbit. Instead, they have evolved extraordinary rotational ability in the neck. Owls, for example, can rotate their neck through 270°.


IPB Image
Some animals of the night have acquired a spherical lens and widened cornea to compensate for reduced eye movement. A spherical lens projects an equally clear image regardless of the light's incoming direction. This combined with a wide cornea effectively increases the animals field of view allowing the head and eyes to remain motionless.
IPB Image Packed With Rods:

The retina of nocturnal animals is almost entirely composed of rods. The other type of vision cells, cones, is absent or almost absent, leaving nocturnal animals with virtually no color vision. The photosensitive pigment inside the rods, rhodopsin, is particularly sensitive to low levels of light. During the day, in a daylight adapted eye, the rhodopsin breaks down so rapidly, it is ineffective for visual perception. At night-time, in the rod-rich eyes of dark-adapted animals, rhodopsin is created faster than it breaks down. Therefore, the threshold of light needed to stimulate the eye is reduced. It is just a minute fraction of the light needed to activate a cone cell for vision during the day.

However, despite being more sensitive to light, the low number of cones means nocturnal animals have sacrificed visual acuity. They must get by with somewhat fuzzy, unfocused images. Only by greatly exaggerating the size of their eyes (and therefore the retinal image), can dark-adapted animals develop reasonable resolution to their images.
Mirrors Add Intensity

On a dark night, flash a bright light at your dog or cat's eyes. What do you see? As if by some mysterious magic, their eyes glow in the dark. But, it is not magic at all. It is the tapetum lucidum (meaning "bright carpet"), an adaptation for night vision. The tapetum is a thick reflective membrane, 15 cells wide, directly beneath the retina. It collects and re-emits light back to the retina a second time, giving the rods a second chance to absorb the image information, thus maximizing the little light available to them. As this light is reflected off the tapetum, the animal's eyes appear to glow.

IPB Image So, although nocturnal animals see mostly crude shapes, outlines and no color, by maximizing their sensitivity to low light levels with the above adaptations, it is enough for them to hunt, feed and survive in the dark of night.
Back In The Daylight

But what happens to these night-time specialists during the day? Most nocturnal animals are largely inactive during the day to avoid over-stimulating their highly sensitive eyes. Nocturnal animals have specialized pupils to shut out damaging bright light.

Pupils are usually circular; it's the most effective shape for allowing light into the eye. Indeed, nocturnal animals dilate their pupils to their circular maximum at night.

IPB Image But by day, the circular pupil is inefficient at blocking light. Instead, a variety of pupil shapes have evolved that limit incoming light, the most advanced being the vertical slit. The slit pupil can shut out all light except a narrow band. Its vertical orientation is of significance too, as it works well with eyelids. As an animal squints, partially closing its lids at right angles to the vertical slit pupil, it further reduces the amount of light entering its eye. Perhaps the most noteworthy of all pupils is the stenopeic pupil of the gecko, a vertical slit lined with notches on each margin. When the pupil is entirely closed, tiny pinholes allow light to pass through to the retina creating sharp overlapping images.
YaarMere
QUOTE(NATURE @ Sep 22 2005, 04:07 AM) *

Aur haa pakaate bhi ho sunglasses2.gif


I didnt get this part. Say again?
NATURE
THANK U AZGAR JI ... for such a nice Article .... here is a short description that I came to know about :
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1. How can we see ? Isn't it the Light that comes from the Object to our Eyes ?
-----> When photon reflects from an object and falls into our eyes, our eyes sense (Hence we see)
It and transmit into an Electrical signal which is sensed by our brain and thus we feel like seeing.

2. How can some Animals like Cats can see in the Dark ? what's the Main difference ?
-----> Some Animals see because they have more number of rods (some cylindrical cell or something!)
In their eyes which help them to amplify that electrical signal. One more thing, the cats' eyes glow in dark,
That's also because of the rods. But human beings have less number of rods, so not much amplification in
Electrical signal, hence we cannot see in dark properly. They have a special layer of cells at the back of
Their retinas, called the Tapetum Lucidum (Latin for "Bright Carpet"). This shiny layer of cells, acting like
A mirror, reflects light back to the retina's cells.

So in near darkness, a cat's eyes collect what light there is and give the retina a second chance to absorb
Every photon. And domestic cats aren't the only ones with this light-enhancing device. Big cats like tigers
And lions, woodland deer, Ocean-dwelling whales and even your family dog all come equipped with the
"Bright Carpet" feature.
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The Next Question is :

Why it happens that in a Hot Sunny Day, we see the air at a far distance is vibrating like Fire ?

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Dear YAARMERE JI ... I think u know Hindi, that's why u didn't ask about the rest ... So No Rewriting ....

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