deletions | additions       diff --git a/Light curves.tex b/Light curves.tex  index 013d9bc..6902cc9 100644  --- a/Light curves.tex  +++ b/Light curves.tex 
...
source, and $d_{ls}$ between lens and source. Note that because of spacetime curvature the lens-source   distance is not the difference between the other two. The time delay distance will be inversely proportional to the Hubble constant $H_0$, the current cosmic expansion rate that sets the scale of the universe, but the distances also involve the matter and dark energy densities, and the dark energy equation of state.   The accuracy of $D_{\Delta t}$ derived from the data for a given lens system is dependent on both the mass model for that system as well as the precision measurement of the lensing observables. Typically, positions and fluxes (and occasionally shapes if the source is resolved) of the images can be obtained to sub-percent accuracy \citep[see e.g.,][]{COSMOGRAIL}, but time delay accuracies are usually on the order of days, or a few percent, for typical systems \citep[see e.g.,][]{TewesEtal2013b}. Measuring time delays requires continuous monitoring over months to years, but years. However,  wide area surveys only return to a given patch of sky every few night, and nights,  sources are only visible from a given point on the Earth(telescope)  for certain months of the year, plus and  bad weather creates can lead to data  gapsin monitoring  as well. \subsection{Simulating light curves}   \label{sec:simulate}