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We have measured the gas temperature in the IC 63 photodissociation region(PDR) using the S(1) and S(5) pure rotation lines of molecular hydrogen withSOFIA/EXES. We divide the PDR into three regions for analysis based on theillumination from $\gamma$ Cas: "sunny," "ridge" and "shady." Constructingrotation diagrams for the different regions, we obtain temperatures ofT$_{ex}$=$562^{+52}_{-43}$ K towards the "ridge" and T$_{ex}$=$495^{+28}_{-25}$K in the "shady" side. The H$_2$ emission was not detected on the "sunny" sideof the ridge, likely due to the photo-dissociation of H$_2$ in this gas. Ourtemperature values are lower than the value of T$_{ex}$=685$\pm$68 K using theS(1), S(3), and S(5) pure rotation lines, derived by Thi et al. (2009) usinglower spatial-resolution ISO-SWS data at a different location of the IC 63 PDR.This difference indicates that the PDR is inhomogeneous and illustrates theneed for high-resolution mapping of such regions to fully understand theirphysics. The detection of a temperature gradient correlated with the extinctioninto the cloud, points to the ability of using H$_2$ pure rotational linespectroscopy to map the gas temperature on small scales. We used a PDR model toestimate the FUV radiation and corresponding gas densities in IC 63. Ourresults shows the capability of SOFIA/EXES to resolve and provide detailedinformation on the temperature in such regions.

Spatial variation in temperature and density in the IC 63 PDR from $\rm H_{2}$ Spectroscopy