Read in the data from your local source

b=.

b = Import["Documents/star2_Richard.txt","Table"];

Length[b]

b[[100]]

b[[1,2]]

Make a data structure      {time, distance}     and plot it.

dist = Table[{b[[i,1]],b[[i,2]]},{i,1,Length[b]}];

dist[[8000]]

g1 = ListPlot[dist,AxesLabel->TraditionalForm/@{"λ (Angstroms)","Flux (arb. units)"},TextStyle->{FontFamily->"Times",FontSize->12},PlotRange->{{6000,6200},{0.6,1.1}}]

g1 = ListPlot[dist,AxesLabel->TraditionalForm/@{"λ (Angstroms)","Flux (arb. units)"},TextStyle->{FontFamily->"Times",FontSize->12},PlotRange->{{6000,6030},{0.6,1.1}}]