The Citizen Tsuki-Yomi “Radio-Controlled” Moon Phase Titanium (Ref. BY1018-80X) is a radio-controlled solar watch launched in 2023 that brings together some of Citizen’s most distinctive technologies in a visually striking configuration. Super Titanium, Eco-Drive power, radio synchronization, perpetual calendar, world time, and automatic moon phase indication coexist within a model designed primarily for those looking for a technologically advanced watch without giving up a traditional analog layout.
The feature that gives it such a distinctive identity is the Luna Program of the Caliber H874. The moon phase is not simply an indication that needs to be periodically corrected: the system uses date information and a mathematical calculation to automatically determine the representation of the Moon. It is this combination of automation, radio control, and analog display that most clearly distinguishes this Tsuki-Yomi within the Citizen range.
Design
The dial is the true visual centerpiece of the watch. Its burgundy-red tone changes in intensity depending on the lighting and creates a bold backdrop for the numerous indications distributed across its surface. Despite the amount of information displayed, Citizen avoids the purely instrumental appearance typical of some radio-controlled watches and maintains a composition that remains recognizable at a glance.
The moon phase indication occupies a prominent position and introduces an almost astronomical element into an otherwise technically focused design. Day of the week, date, 24-hour indication, and functional scales add depth to the dial without turning it into a digital display disguised as an analog watch.
The contrast between the warm-toned dial and the metallic elements of the case helps give the model its distinctive personality. The titanium bracelet visually continues the surfaces of the case and creates a coherent overall appearance, while the darker details surrounding the dial increase the visual separation between the functional and structural elements.
The result is not a minimalist dress watch. The Tsuki-Yomi deliberately showcases its complexity and is aimed at those who appreciate information-rich dials, visible technology, and contemporary aesthetics.
Case & Construction
The case is made from Super Titanium, a material central to Citizen’s watchmaking and treated here with Duratect TIC surface hardening. The advantage is not limited to resistance to wear: titanium helps reduce the weight of a watch with substantial proportions, improving its practicality for everyday use.
The case measures 43 mm in diameter and 10.9 mm in thickness, with a lug-to-lug distance of approximately 47.6 mm. The lug width is 22 mm. These proportions result in a relatively slim profile compared with the diameter, an important consideration given the amount of technology integrated into the movement and dial.
Protecting the dial is a sapphire crystal with anti-reflective treatment. This choice is consistent with the positioning of the watch and contributes both to scratch resistance and to the legibility of a particularly complex dial.
The construction also provides 100 meters of water resistance, sufficient to handle everyday use and more active situations without the concerns typically associated with a simple dress watch.
Movement
At the heart of this Tsuki-Yomi is the Citizen Eco-Drive H874, a light-powered quartz movement developed in Japan. In this case, the value of the caliber lies not only in the precision typical of its electronic architecture, but above all in the level of automation it achieves.
Eco-Drive eliminates the need for conventional periodic battery replacement by using light energy to recharge the internal power cell. When fully charged, the watch offers approximately 6 months of autonomy, which can extend to around 30 months, equivalent to 2.5 years, when the power-saving mode is activated.
The radio-controlled system allows the movement to synchronize the time indication with compatible radio signals in areas covered by the system. This is complemented by shock detection and automatic hand position correction, solutions designed to preserve the correspondence over time between the electronic information processed by the caliber and what is actually displayed on the dial.
The H874 also offers magnetic resistance and a power reserve indication. Overall, it is a movement designed to minimize the amount of intervention required from the owner once the watch has been correctly configured.
Functions & Complications
The most distinctive function is the Luna Program. The system mathematically determines the moon phase using date information and automatically updates its representation on the dial. It is also possible to select the appropriate display for the Northern or Southern Hemisphere.
Alongside the Moon, there are day-of-the-week and date indications, while the perpetual calendar is programmed through February 28, 2100. The 24-hour indication makes it possible to distinguish AM from PM immediately.
The World Time function manages 24 time zones and makes the model particularly interesting for travelers. The system also includes automatic or manual daylight saving time management, while radio control allows it to keep the time and calendar information synchronized whenever a compatible signal is available.
It is precisely the integration of these functions that represents one of the greatest strengths of the H874: moon phase, calendar, and time indication do not operate as completely independent elements, but form part of a system designed to require as few manual adjustments as possible.
Performance
With a diameter of 43 mm, the Tsuki-Yomi maintains a noticeable presence on the wrist, but its relatively compact lug-to-lug distance of approximately 47.6 mm helps prevent the case from extending excessively across the wrist. The 10.9 mm thickness is particularly noteworthy for a model that integrates such a large number of functions and allows the case to maintain a less bulky profile than its diameter might suggest. The 22 mm lug width also helps create balanced proportions between the case and the Super Titanium bracelet.
Super Titanium becomes particularly important during extended wear. Its lower weight compared with an equivalent steel construction reduces the sensation of mass on the wrist and makes a case of this size easier to manage. The bracelet, made from the same material, also helps maintain an even distribution of weight.
The fold-over clasp with safety push buttons prioritizes practicality and stability during everyday use. The watch nevertheless retains a substantial visual presence: if you prefer very compact cases, you may find the 43 mm diameter rather large, especially if you have a smaller wrist.
Legibility also deserves specific consideration. There is a considerable amount of information available, and a certain degree of familiarity is required to interpret all the indications quickly. Once you become accustomed to the dial layout, however, the separation between the various functions makes the watch more intuitive to use than its initial complexity might suggest.
Technical Data
Brand: Citizen Watches;
Model: Citizen Tsuki-Yomi “Radio-Controlled” Moon Phase Titanium (Ref.BY1018-80X);
Year: 2023;
Case Material: Super Titanium with Duratect TIC Surface Hardening;
Case Diameter: 43 mm;
Case Thickness: 10.9 mm;
Lug Width: 22 mm;
Lug-to-Lug: ~47.6 mm;
Crystal: Sapphire Crystal with Anti-Reflective Treatment;
Water Resistance: 100 m / 330 ft (10 ATM);
Power Reserve: ~6 months (up to ~30 months / 2.5 years in Power-Save Mode);
Movement: Eco-Drive Watches, Quartz Watches, Radio-Controlled Watches, Solar Watches – Citizen Eco-Drive Caliber H874 (Japanese Movement);
Functions: Hours, Minutes, Seconds, 24-Hour Indication, Radio-Controlled Atomic Timekeeping, World Time (24 Time Zones), Automatic / Manual Daylight Saving Time Adjustment, Perpetual Calendar (until February 28, 2100), Power Reserve Indication, Magnetic Resistance, Shock Detection, Automatic Hand Correction;
Complications: Fully Automatic Moon Phase Display (Luna Program with Mathematical Moon-Phase Calculation and Northern / Southern Hemisphere Selectable Display), Date Display, Day Display;
Bracelet / Strap: Super Titanium Bracelet with Duratect TIC Surface Hardening and Fold-Over Clasp with Push Buttons;
Type: Calendar Watches, Classic Watches, Moon Phase Watches, Tool Watches, Travel Watches;
Sex: Men’s Watches;
Nationality: Japanese Watches.
Retail Price (Launch): €698 / $850.
The Citizen Tsuki-Yomi “Radio-Controlled” Moon Phase is particularly interesting because it does not treat technology as a simple addition to a traditional analog watch. Eco-Drive, radio control, perpetual calendar, and Luna Program work together to create a timepiece centered on automation and on reducing the number of adjustments required from the wearer.
Among its main strengths are the H874 caliber, extended autonomy, the lightness of Super Titanium, sapphire crystal, World Time function, and above all its automated moon phase display, which represents something more sophisticated than a conventional manually adjusted moon phase complication.
The main compromise, however, is the density of the dial. If you are looking for absolute immediacy or minimalist aesthetics, you may find the amount of information displayed excessive. The 43 mm diameter also makes the watch better suited to those who appreciate a pronounced wrist presence, although titanium, the relatively slim profile, and the compact lug-to-lug measurement help mitigate its overall dimensions.
Considering the level of integrated technology, materials, and available functions, the relationship between features and price remains one of the model’s most compelling aspects. This is not a nostalgic reinterpretation of the traditional mechanical moon phase: it is a distinctly Citizen interpretation of the complication, built around precision, light-powered energy, and automation. And it is precisely this technological identity that makes the Tsuki-Yomi different from most analog moon phase watches in the same market segment.
You can explore current auctions and listings for this watch on Catawiki using the search link below.
