為什麼氧氣沒有影子?

小分子的影子太細，用肉眼係看不見的。但是，大分子（污染物氣體）係會吸光的，晚上看星星會好明顯有影響，又或者日間看遠野越遠就越濛。

所有分子都會吸收微量的的光子，但係，因為空氣分子密度相若（平均氣壓約1000kPa左右，低過 950kPa已經好大機會八號風球），加上氧氣收光極微，有差距肉眼都唔多覺。

Visble light is of wavelength 400 nm to 700 nm (i.e. 4x10^-7 m to 7x10^-7 m), which is much longer than the diameter of an atom (less than 10^-10 m ). As such, diffraction effect will be much pronounced and you will not be able to see these atoms.

This is similar to the situation that you cannot detect the presence of a book placed between you and a sound source just simply by hearing with your ears, because of the diffraction of sound wave (sound has a wavelength much longer than the dimension of a book).

在物理界, 有多種物質能吸收電磁波(光是電磁), 阻隔電磁波(像铝與X 光) 或讓電磁波(伽碼射線)通過. 吸收及阻隔的效能完全視該種物質份子之間的間距是否能阻擋電磁波, 這可以從電磁波的波長給出. 所以O2的份子之間能讓電磁波的電波及磁波通過和重合, 就不可能出現影子.

因為氧粒子體積極小 而且分佈極散 無法組成一個有組織性的影子
其實有極細小的影子 只是肉眼無法經反射而發覺有氧氣影子存存