Citizen Tsuki-yomi A-T Moonphase 43mm Eco-Drive Watch #BY1010-57H

Model Reference: BY1010-57H

Overview
The Citizen Tsuki-yomi is a poetic fusion of high-technology and astronomical art. Its defining characteristic is the textured grey dial, which is meticulously crafted to resemble the craters and "seas" of the lunar surface. Housed in a refined 43mm silver-tone stainless steel case, it uses the Caliber H874 to achieve a feat never before seen in analog horology: an automatic moon phase that adjusts itself via radio signals. This "Moon Reader" eliminates the need for the manual corrections typically required by mechanical moon phase watches, ensuring the lunar display is as accurate as an atomic clock.

Technical Specifications

Case Size: 43mm (Contemporary, architectural profile)

Case Material: Silver-Tone Stainless Steel (High-polish and brushed finishes)

Movement: Eco-Drive (Caliber H874; Radio-Controlled Atomic Timekeeping with automatic moon phase)

Crystal Type: Sapphire Crystal (Anti-reflective coating for a "disappearing glass" effect)

Water Resistance: 100 Meters (10 ATM / 333 feet) — Designed for everyday versatility and swimming

Dial: Moon-surface textured grey dial with a specialized lunar sub-dial at 6 o'clock

Bezel: Fixed silver-tone stainless steel

Strap: Silver-tone stainless steel integrated-style link bracelet

Special Features

The "Luna Program": This is the heart of the Tsuki-yomi. The watch receives time signals from atomic clocks and uses a proprietary internal mathematical formula to calculate the moon's phase, automatically rotating the display to match the sky perfectly.

Geographic Moon Phase Shift: Unlike standard moon phase watches, the Tsuki-yomi can be toggled to show the moon as it appears from either the Northern or Southern Hemisphere.

Lunar Surface Artistry: The dial isn't just a color; it’s a three-dimensional representation of the moon’s topography. The shadows and highlights on the dial change as light hits it from different angles, mimicking a moonlit night.

Atomic Precision: Syncs automatically across four global regions (North America, Europe, China, and Japan) for split-second accuracy in time and date.

Perpetual Calendar: Seamlessly manages the transition between months of varying lengths and leap years without manual intervention.

Light Level Indicator: A sub-dial at 12 o’clock serves a dual purpose, showing the energy reserve and the current light-charging efficiency of the Eco-Drive cell.

World Time Functionality: Provides instant access to the time in 26 world cities by simply moving the second hand to the desired city code on the outer ring.

Super-LumiNova Accents: The hands and hour markers are treated with high-performance lume, echoing the "glow in the dark" theme of the moon itself.