not 光速，it should be 光束, which means light beam. not 两了半天，it should be 亮了半天,which means bright for a half-day. the first sentence means: only leaving its light beam in the sky, which faded for a half-day,

改天： some other day/ someday in the near future 我要：I'm going to/ I will 朝他拍桌子：tell him that I'm fed up with him and I'm really pissed off so that I've make up my mind to quit the job. here"拍桌子"is a metaphor, you don't literally hit or bang the office table. hope it helps

拍桌子 means "strike the table",when we`re angry,we usually strike the table ,stand up and shout to others,so in this sentence ,it actually means you`re showing anger,改天我要对他拍桌子means I`ll be sure to work my anger out on him one day.the first Chinese sentence isn`t correct ,although I can guess its meaning, but I`m unable to explain it to you as my English is quite poor....