Earth's radiation budget (ERB) is an essential climate variable, and its continuous observation from space is critical to understanding long-term climate change. The Clouds and Earth's Radiant Energy System (CERES) has maintained the longest continuous ERB record since 2000, with its follow-on mission, Libera, launching in 2027 with a 5-year prime mission lifetime. Beyond Libera, plans for ERB continuity remain uncertain, increasing the possibility of future gaps in the record. The Compact Total Irradiance Monitor (CTIM) was a 6U CubeSat developed under the NASA In-Space Validation of Earth Science Technologies (InVEST) program to measure total solar irradiance (TSI). Launched in July 2022 and operating until November 2023, CTIM collected climate-quality science at an uncertainty of 0.017 %. During orbital eclipse, CTIM was pointed in the nadir direction to measure Earth's outgoing longwave emission, exploring the Earth-observing potential of an instrument designed for TSI. These measurements were compared to coincident CERES observations aboard Terra, Aqua, and NOAA-20. Additional adjustment factors for limb darkening were derived from radiative transfer simulations over a variety of scene types and atmospheric conditions and applied to CERES non-nadir viewing observations to better match the CTIM nadir observations and explain some of the variance exhibited between measurements. The resulting comparisons show an overall relative agreement of 1.3 %, within respective instrument uncertainties. This study demonstrates that leveraging CubeSat technology could complement heritage ERB missions and reduce the risk of future observation gaps. The routine inclusion of Earth-viewing capabilities in future TSI instrument designs represents a natural extension of this work, with the potential to meaningfully contribute to ERB observation continuity and reduce dependence on dedicated large-scale missions.