Precise calibration of spectrometers over a wide spectral range at observatories is essential for detecting tiny cosmological frequency shifts caused by time variations of the fundamental constants, universe’s expansion history, and earth-size extrosolar planets. Optical frequency combs (OFCs) are ideal rulers for calibrating the astro-spectrometers due to their regularly-spaced absolute frequencies over wide range of wavelengths. To resolve each mode of the OFC using spectrometers at observatories, the repetition rate of the OFC should be larger than the resolutions of the spectrometers which are typically on the order of 10 GHz. We constructed a compact astro-comb consisting of a 1.6 GHz-Ti:Sapphire OFC and a Fabry-Perot cavity that increases the mode spacing. The output spectrum of the 1.6 GHz OFC ranges roughly from 500 nm to 1100 nm. Every 27th mode of the fundamental comb transmits the cavity to form an astro-comb with a repetition rate of 43.2 GHz. In this talk, I will summarize the experimental setup and the spectrum of the astro-comb in the green region taken at the Okayama astrophysical observatory, and discuss future improvements.