Two true skies, computed independently
The twin poster is really two complete star maps on one sheet. For each side you supply a caption such as “The Night We Met” or “The Night We Married”, a calendar date, an optional clock time and a place — either a city from the built-in list of 350 worldwide cities or exact custom latitude and longitude. Every side is then computed separately through the same astronomical pipeline as our main star map: the moment becomes a Julian Day, the Meeus sidereal-time formula gives the Earth's rotation angle relative to the stars, the place's east longitude produces Local Sidereal Time, and all 327 measured stars of the ATHYG catalog are transformed from J2000 equatorial coordinates into local altitude and azimuth. Stars beneath the horizon are discarded independently for each side, so a wedding in Tokyo and a first meeting in Lisbon each show their own correct hemisphere rather than one copied pattern.
Both disks use a stereographic projection of the visible sky with the same orientation — north at the top, east and west mirrored correctly — and share one color theme so the pair reads as one artwork while remaining individually accurate. Constellation stick figures are drawn only when both endpoints of a segment are above the horizon, brighter stars are sized by visual magnitude, and optional diffraction rays mark the most luminous points. Because each disk recomputes the full sky, the two moments may be hours or decades apart, in different countries or hemispheres, and each map stays faithful to its own date and meridian.
The heart between the maps and the print file
A hand-drawn Bézier heart links the two disks by default; switch it to a discreet cross for a friendship print or an ampersand for a wedding couple's edition. Beneath each circle the poster sets the caption, the full local date and time, the place name or coordinates, in matching serif typography. A preview at 1200 logical pixels shows both circles updating simultaneously as you edit either side, while Download repaints the complete composition at 300 dots per inch in your chosen A4, A3, 16×20, 18×24, 24×36 or square format, with a small Memory Poster Studio brand line. Nothing leaves your device: both dates, places and captions are processed in the browser for a free, watermark-free and completely private anniversary keepsake.
两片真实的天空，各自独立计算
双人海报本质上是把两张完整的星图放在同一张纸上。每一侧你都可以填写小标题（如「相遇之夜」或「结婚之夜」）、公历日期、可选的钟表时间与地点——地点可选内置 350 个世界城市之一，也可直接填写精确的自定义经纬度。两侧会分别走过与主星空地图完全相同的天文管线：时刻先换算为儒略日，再用 Meeus 恒星时公式求出地球相对恒星的自转角，加上地点东经得到地方恒星时；ATHYG 星表中全部 327 颗实测恒星都从 J2000 赤道坐标换算为当地高度角与方位角。地平线以下的恒星在两侧各自独立剔除，因此东京的婚礼与里斯本的初见，显示的是各自正确的半球，而不是同一张图复制两遍。
两个圆盘都采用可见天空的立体投影，朝向规则一致——北在上，东西方向镜像正确——并共用同一套配色主题，让两张图既是一组作品，又各自精确。星座连线只在线段两端都在地平线以上时才绘制，恒星按视星等决定大小，最亮的点还可选择加上衍射光芒。由于每个圆盘都会独立重算整片天空，两个时刻即使相隔数十年、分处不同国家甚至不同半球，每幅星图依然忠于各自的日期与子午线。
星图之间的心形与印刷文件
两个圆盘之间默认以手绘贝塞尔心形相连；用于友情纪念时可换成低调的交叉号，用于婚礼主题也可换成和号「&」。每个圆环下方都用统一的衬线字体排印小标题、完整当地日期与时间、城市名或坐标。1200 逻辑像素的预览中，编辑任一侧时两个圆盘都会同步刷新；点击下载时，整幅作品会按 A4、A3、16×20、18×24、24×36 或方形尺寸，以每英寸 300 点从零重绘，并带一行小巧的 Memory Poster Studio 品牌字样。所有信息都不会离开你的设备：两个日期、地点与小标题全部在浏览器本地处理——一份免费、无水印且完全私密的周年纪念。
Can the two nights be in different cities or countries?
Yes — each side has its own place menu and its own custom-coordinates option. A first meeting in Paris and a wedding in New York are both rendered from their own latitude, longitude and local time. You can even place the two events in opposite hemispheres; the stereographic disks remain individually correct.
两个夜晚可以在不同城市甚至不同国家吗？
可以。每一侧都有独立的地点下拉与自定义坐标栏。在巴黎初遇、在纽约结婚，会分别按各自的纬度、经度与当地时间绘制；两幕事件即使分处南北半球也没问题，两个立体投影圆盘各自保持正确。
What if one exact time is unknown?
Leave that side's time box empty and 22:00 is used automatically. The sky rotates only about one degree every four minutes, so an estimated evening hour moves the stars by less than most people notice, while both posters still render correctly side by side.
其中一个具体时间不知道怎么办？
把那一侧的时间栏留空，即自动使用 22:00。星空每四分钟才转动约一度，所以晚间时刻相差一两个小时，星点移动微乎其微，两张星图并排依旧都准确美观。
Which ornament should I choose for a wedding or anniversary print?
The heart suits anniversaries, engagements and the night you met; the ampersand reads elegantly on wedding stationery; the plain cross keeps the design neutral for friendship or family milestones. All three are drawn as vectors, so they remain crisp at 300 DPI even in the 24×36 inch size.
婚礼或周年纪念印刷，选哪种连接装饰？
心形适合周年纪念、订婚与相遇之夜；和号「&」在婚礼纸品上优雅耐看；简洁的交叉号则适合友情或家庭里程碑等中性主题。三种装饰都是矢量绘制，即便在 24×36 英寸尺寸下以 300 DPI 输出也依旧清晰。
