问答 · 10 questions
Straight answers, no scrolling.
这些是大家真的会输进搜索框的问题，用两三句话回答。与时间有关的答案按北京计算，并且会写明。
What time does the sky get properly dark tonight?
From Beijing (39.90, 116.41), astronomical darkness runs from 18:52 to 05:10 当地时间 — about 10.3 hours. "Properly dark" means the Sun is more than 18° 地平线下 the horizon, which is when the sky background stops hiding faint objects.
更多 →Can I see the space station tonight?
Yes — the next visible pass over Beijing starts at 19:02 当地时间 and peaks 63° above the horizon to the north-north-west. It rises in the west and disappears in the east, and lasts about 10 minutes.
更多 →Which planets can I see tonight?
From Beijing tonight the planets clearing 10° are 火星, 木星, 土星. 火星 is the highest at 60° to the south-east. Anything 地平线下 10° is usually lost behind buildings and haze, whatever the sky conditions.
更多 →What does 计划发射 mean on a launch schedule?
计划发射 stands for "No Earlier Than" — the earliest moment the vehicle could launch given what is currently known. It is a floor, not an appointment: dates slip backwards far more often than forwards, and a launch scrubbed at T-30 seconds gets a new 计划发射.
更多 →How fast does the 空间站 move?
约 7.66 km/s，也就是大约 27,600 km/h——每 92 分钟绕地球一圈。所以它横穿天空只要四到六分钟，也因此每天傍晚的好过境会提前几分钟。
更多 →为什么有些很亮的行星反而看不到？
Because visibility is a geometry question, not a brightness one. A planet 地平线下 your local horizon is on the other side of the planet, and one low above the horizon is seen through several thicknesses of atmosphere that smear it into a wobbling blob.
更多 →民用、航海、天文三种暮光有什么区别？
They are defined by how far the Sun is 地平线下 the horizon: 6°, 12° and 18°. Civil twilight ends when street lights matter, nautical when the sea horizon disappears, and astronomical when the sky background is finally dark enough for faint objects.
更多 →Do I need a telescope to see 土星's rings?
能，但差别不大。土星环与本体之间约需 30 倍，所以 70–90 mm 的小望远镜配稳的三脚架就够；双筒望远镜分辨不出来。这个价位上，架子比口径更重要。
更多 →卫星过境预报有多准？
Good to seconds for a day-old element set, and to a few minutes for a week-old one. We propagate the latest Celestrak TLE with SGP4 locally in your browser, so the table is as fresh as the element set and the page says when it was fetched.
更多 →下一次火箭发射是什么时候？
The next orbital launch on our board is GSLV Mk II | IRNSS-1L (NVS-03), 计划发射 2026-10-30 18:21 UTC, from Satish Dhawan Space Centre Second Launch 发射台. Launch times move; the board prints the age of its snapshot on every page so you can see how current that is.
更多 →The full picture
一条轴上铺开日落至日出，标出能升到地平线之上的目标。