看見今晚的月亮：拖曳月相弧線，晨昏線就會連續掃過月面 See tonight's moon: drag the lunation arc to sweep the terminator 今夜の月を見る：月相弧線をドラッグして明暗界線を連続的に動かす
月相時刻用 Meeus《天文演算法》第 49 章 k/T 週期序列與週期修正項求出；月球位置與亮面比例用第 47/48 章的獨立序列計算。兩組演算法互相驗證：在任一新月時刻，獨立計算的亮面比例應低於 1%；在任一滿月時刻應超過 99%。相位時刻以 ΔT 多項式從動力時（TD）換算為世界時（UT），再轉成您的當地時區。 Phase instants are computed from the k/T series with periodic corrections (Meeus, Astronomical Algorithms, Ch. 49). Moon position and illuminated fraction are computed from an independent series (Ch. 47/48). The two engines cross-check each other: at every new-moon instant the independently computed illuminated fraction should be below 1%, at every full moon above 99%. Phase instants are converted from Dynamical Time (TD) to Universal Time (UT) using a ΔT polynomial, then displayed in your local timezone. 月相時刻は Meeus「天文計算」第49章の k/T 周期級数と周期補正項で求めます。月の位置と輝面比は独立した第47/48章の級数で計算します。両エンジンは相互検証されます：新月時刻では輝面比が1%未満、満月時刻では99%超となるべきです。相位時刻はΔT多項式により力学時（TD）から世界時（UT）に変換し、お使いのタイムゾーンで表示されます。
月面的晨昏線是一條半橢圓曲線：在上弦和下弦時退化為一條直線；在盈月到滿月之間朝暗側彎曲；在新月到上弦之間朝亮側彎曲。亮面和暗面相同亮面比例的月相，晨昏線互為鏡像。南半球視角切換會將整個月面旋轉 180 度——不是左右鏡射。南半球觀察者看到的是同一個月面倒過來，所以彎月方向相反，而月海的相對位置仍然正確；鏡射會畫出一個不存在的月亮。 The terminator on the moon disc is a half-ellipse: it degenerates to a straight line at the quarters, bows toward the dark side during gibbous phases, and bows toward the lit limb during crescent phases. Waxing and waning phases of equal illumination are mirror images of each other. The southern-hemisphere toggle rotates the whole disc by 180 degrees — it is not a mirror. Southern observers see the same face upside down, so the crescent curves the other way while the maria stay in their true relative positions; mirroring would draw a Moon that cannot exist. 月面の明暗界線（ターミネーター）は半楕円の曲線です：上弦・下弦では直線に退化し、十五夜前後では暗側に湾曲し、三日月前後では明縁側に湾曲します。同じ輝面比の上弦側・下弦側は鏡像関係になります。南半球表示に切り替えると、月面全体が180度回転します——左右反転ではありません。南半球では同じ月面が上下逆に見えるため三日月の向きが逆になりますが、海の相対位置は正しいままです。鏡像反転では存在しない月になってしまいます。
農曆「初幾」的計算：農曆每月初一，依定義就是含該次新月時刻（以 UTC+8 計）的那一天。本工具直接用自己算出的新月時刻往回數 UTC+8 的日曆天，得出初幾，無需查表。範圍限於初幾，不做月份編號與閏月判斷。有時滿月會落在十六而非十五，因為月相是一個時刻，不是整天。此工具不做月出月落、觀測者座標、天秤動、日月食預測，也無任何占星內容。 The lunar day-of-month is derived from this tool's own new-moon instant: the first day of each lunar month is defined as the civil day (UTC+8) that contains the new-moon instant. The tool counts civil days forward from that point — no lookup table is needed. Only the day-of-month is computed here; lunar month numbering and intercalary months require solar-term rules and are out of scope. The full moon sometimes falls on day 16 rather than 15 because a phase is an instant, not a whole day. This tool does not compute moonrise/moonset, observer coordinates, libration, eclipse prediction, or any astrological content. 旧暦の日付は、このツール自身の新月時刻から計算します。旧暦一日は定義上、新月時刻（UTC+8）を含む日です。ツールはその日から何日経過したかを数えるだけで、参照テーブルは不要です。月の番号や閏月の判定には節気の規則が必要なため、このツールの対象外です。満月が十五日でなく十六日に当たることがありますが、月相は一瞬の出来事であり一日全体ではないためです。月の出没、観測者の座標、秤動、日月食の予測、占星術的な内容は対象外です。
月面影像來自 NASA 科學視覺化工作室（Scientific Visualization Studio）的「CGI Moon Kit」，由月球勘測軌道飛行器（LRO）廣角相機超過十萬張影像合成。原始的等距長方投影圖已由本站重新投影成正面正射投影，工具再把自行計算出的晨昏線疊上去。NASA 影像屬公有領域；此處的使用與 NASA 無隸屬關係，也不代表其背書。 The lunar surface is NASA's Scientific Visualization Studio "CGI Moon Kit", assembled from over 100,000 Lunar Reconnaissance Orbiter Wide Angle Camera images. The source equirectangular map was reprojected here into the orthographic near-side view, and the tool draws its own computed terminator on top. NASA imagery is in the public domain; this use is not affiliated with, nor endorsed by, NASA. 月面画像は NASA サイエンティフィック・ビジュアリゼーション・スタジオの「CGI Moon Kit」で、月周回無人衛星 LRO の広角カメラ画像10万枚以上から合成されたものです。元の正距円筒図法の地図を本サイトで正射図法の表面図に再投影し、その上に独自計算の明暗界線を重ねています。NASA の画像はパブリックドメインです。本ツールは NASA と提携しておらず、NASA が推奨するものでもありません。
Quick guide
Compact below-tool notes that help first-run users and repeated visitors move faster without changing the main interface.
Chinese search: 今天月相、今晚月亮、下次滿月 時間、農曆 初幾 月相、月相 查詢
Japanese search: 月齡 今日、満月 いつ、今日 月相、次の満月、月の満ち欠け
How to use
Examples
FAQ
No internet required. All phase data is computed in your browser using astronomical algorithms: phase instants from a k/T series with periodic corrections, and the moon's position and illuminated fraction from an independent series. No backend, no database.
Not from a lookup table. The first day of each lunar month is defined as the civil day (UTC+8) containing the new-moon instant. The tool counts days forward from that point using its own computed new-moon times.
A phase is an instant, not a whole day. The full moon can fall on either day 15 or 16 depending on when the exact instant occurs in your timezone. The tool labels which timezone it's using.
Yes. 'Share this moment' copies a URL carrying the date (for example ?d=2026-07-17T20:00), and it opens on that exact moon rather than jumping to today. The birth-moon share includes the same link. The timestamp is local wall-clock time, matching the date field on screen.
Yes. The surface is NASA's Scientific Visualization Studio 'CGI Moon Kit', assembled from over 100,000 Lunar Reconnaissance Orbiter Wide Angle Camera images and in the public domain. It is reprojected here into the near-side view, with the tool's own computed terminator drawn over it. The southern-hemisphere view rotates the whole disc 180 degrees rather than mirroring it — a mirrored Moon is one that cannot exist.
Yes. The southern hemisphere sees the same face upside down — a 180-degree rotation, not a mirror. The illuminated fraction is identical but the crescent curves the other way, while the maria keep their true relative positions. The hemisphere toggle does exactly that; mirroring would render a Moon that cannot exist.
Moonrise/moonset times, observer coordinates, libration, eclipse prediction, supermoon distance, and any astrological content. The tool answers one question: what does the moon look like at that instant?