"hello" and second problem with time machines.

You are walking along the road, lost in thoughts, and suddenly some stranger (usually a security-man) says Hello/GoodMorning/GoodEvening. That was something unusual for me to get used to after coming here. 

My first reaction was to freak out, oh, Who is this guy! Why is he smiling at me! Is there something wrong with my clothes?

Later I managed to force a smile under such situations and learnt to quickly reciprocate the greeting. But one needs a good reaction time. Often these fellow greeters have a lot of time to plan their hello, whereas we, the victims, don't know which way the next hello might be coming from. 

Even now, sometimes I get startled by unexpected hellos and then sheepishly realize after walking forward that I haven't properly reciprocated. And then I wonder whether he's wondering if I'm rude or something. Shrug!

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http://www.markhintonstewart.com/TheManFromEarthMusic.html

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First problem with time travel is time travel itself, but the second problem is that of space travel.

Time travel writers seem to forget a crucial detail about journey back into time. They will show the time and place on their time machines, but they never mention the reference frame of co-ordinates.

Given that the earth is rotating around the sun and itself, the calculations about where in space the destination is, must be difficult to make. Besides, the solar system itself is moving in the universe at its own velocity. It's possible that the dinosaurs were at a particular x, y, z place in the space where we have never been to again in history. And without knowing what those x, y and z were, how can we build a time machine that will take us there?

PS. There may be something wrong with the logic above.