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Transits of hot Jupiters in X-rays and the ultraviolet have been shown to beboth deeper and more variable than the corresponding optical transits. Thisvariability has been attributed to hot Jupiters having extended atmospheres atthese wavelengths. Using resolved images of the Sun from NASA's Solar DynamicsObservatory spanning 3.5 years of Solar Cycle 24 we simulate transit lightcurves of a hot Jupiter to investigate the impact of Solar like activity on ourability to reliably recover properties of the planet's atmosphere in softX-rays (94 {\AA}), the UV (131-1700 {\AA}), and the optical (4500 {\AA}). Wefind that for stars with similar activity levels to the Sun, the impact ofstellar activity results in the derived radius of the planet in soft X-ray/EUVto be underestimated by up-to 25% or overestimated by up-to 50% depending onwhether the planet occults active regions. We also find that in up-to 70% ofthe X-ray light curves the planet transits over bright star spots. In the farultraviolet (1600 & 1700 {\AA}), we find the mean recovered value of theplanet-to-star radius ratio to be over-estimated by up-to 20%. For opticaltransits we are able to consistently recover the correct planetary radius. Wealso address the implications of our results for transits of WASP-12b and HD189733b at short wavelengths.

Transiting the Sun: The impact of stellar activity on X-ray and ultraviolet transits