need help solving extra credit riddle

[Belties R Us]

I am nothing without it, one "n-less" word;
I am he without breath, placed after the third.
In a fortnight I'm there, where before I've been;
If you see my reflection, you'll know what I mean.

What am I?

Its for chemistry class extra credit. Please help.

 

[Caustic Burno]

If I am reading the riddle correctly my take is. " oxygen is a Group 16 element. While about one fifth of the atmosphere is oxygen gas, the atmosphere of Mars contains only about 0.15% oxygen. Oxygen is the third most abundant element found in the sun, and it plays a part in the carbon-nitrogen cycle, one process responsible for stellar energy production. Oxygen in excited states is responsible for the bright red and yellow-green colours of the aurora. About two thirds of the human body, and nine tenths of water, is oxygen. The gas is colourless, odourless, and tasteless. Liquid and solid oxygen are pale blue "

Solar System is endless
There is death without it and it is the third most abundant element.
Stellar energy is reflected off the moon that waxes and wanes every fortnight.
Lastly it is blue in color as water and you could see your reflection.

Been a while since chemistry.

 

[mmsubs]

http://www.cattletoday.com/forum/viewtopic.php?f=6&t=64766