Repetitive patterns in rapid optical variations in the nearby black-hole binary V404 Cygni.

How black holes accrete surrounding matter is a fundamental yet unsolved question in astrophysics. It is generally believed that matter is absorbed into black holes via accretion disks, the state of which depends primarily on the mass-accretion rate. When this rate approaches the critical rate (the Eddington limit), thermal instability is supposed to occur in the inner disk, causing repetitive patterns of large-amplitude X-ray variability (oscillations) on timescales of minutes to hours.

How Many Days in a Year Can Mt. Fuji and the Tokyo Tower Be Seen from the Tokyo Suburban Area?

Mt. Fuji and the Tokyo Tower were observed daily from the Seikei Meteorological Observatory in Tokyo for the past 30 years. The observatory recorded whether each object could be seen at 9:00 a.