This page collects the more commonly used terms in astronomical observation and astrophotography, grouped by topic. Each entry gives a one-sentence definition, with units, value ranges, typical values or formulas where helpful; for systematic study, follow the link to the corresponding main page. Beginners can start with the Getting Started guide.
A coordinate measured eastward from the vernal equinox along the celestial equator, analogous to longitude; expressed in hours, minutes and seconds (0h–24h, with each 1h corresponding to 15°). See Celestial coordinate systems.
赤纬
Declination, Dec
The angular distance of an object from the celestial equator, analogous to latitude; ranges from −90° (south celestial pole) to +90° (north celestial pole), with the celestial equator at 0°.
地平高度
Altitude, Alt
The elevation angle of an object relative to the horizon, from −90° (nadir) to +90° (zenith), with 0° on the horizon.
方位角
Azimuth, Az
The directional angle measured along the horizon, usually clockwise from due north; 90° is due east and 180° is due south.
时角
Hour Angle, HA
The angular distance of an object from the local meridian, measured in hours; HA = local sidereal time − right ascension, equal to 0 at transit.
黄道
Ecliptic
The path of the Sun’s apparent annual motion across the celestial sphere, inclined about 23.44° to the celestial equator (the obliquity of the ecliptic).
春分点
Vernal Equinox / First Point of Aries
The ascending node of the ecliptic and the celestial equator, serving as the zero point from which right ascension is measured.
中天
Culmination / Meridian Transit
The moment an object crosses the local meridian and reaches its highest altitude. See Diurnal apparent motion.
岁差
Precession
The slow gyration of Earth’s axis that causes the vernal equinox to drift westward and the coordinate epoch to change, with a period of about 25,800 years.
历元
Epoch
The specific reference instant to which coordinates are referred; the current standard is J2000.0.
恒星时
Sidereal Time
Time referenced to the stars, numerically equal to the right ascension of the star currently transiting the meridian. See Time systems.
当地恒星时
Local Sidereal Time, LST
The sidereal time at the observer’s longitude, equal to the right ascension currently on the meridian.
协调世界时
Coordinated Universal Time, UTC
The globally unified civil time standard; astronomical records and plans are often labeled in UTC.
儒略日
Julian Date, JD
A continuous count of days since 4713 BC, convenient for computing precise time intervals; the JD count begins at noon.
A logarithmic scale of an object’s brightness as seen from Earth, where smaller values are brighter; the Sun is about −26.8 and the naked-eye limit about +6.5. See Magnitude and brightness.
绝对星等
Absolute Magnitude, M
The apparent magnitude an object would have if placed at 10 parsecs, reflecting its intrinsic luminosity.
普森比
Pogson Ratio
The conversion between magnitude and brightness: a difference of 1 magnitude is about a factor of 2.512, and a difference of 5 magnitudes is exactly a factor of 100, with brightness ratio = 10^(0.4·Δm).
面亮度
Surface Brightness
The brightness per unit area of an extended source, measured in magnitudes per square arcsecond, which determines the visibility of diffuse objects.
极限星等
Limiting Magnitude
The faintest magnitude detectable with a given setup and under given sky conditions.
光度
Luminosity, L
The total energy an object radiates per unit time in all directions, measured in watts (W) and often expressed in units of the solar luminosity L☉.
秒差距
Parsec, pc
The distance at which the annual parallax is 1 arcsecond, about 3.26 light-years.
视差
Parallax
The periodic shift in the position of a nearby star caused by Earth’s orbital motion, used for trigonometric distance measurement.
自行
Proper Motion
The angular rate of a star’s motion across the celestial sphere perpendicular to the line of sight, measured in arcseconds per year.
红移
Redshift, z
The shift of spectral lines toward longer wavelengths, z = Δλ/λ, reflecting recession velocity or cosmic expansion. See Cosmology overview.
光谱型
Spectral Type
The sequence of stellar classification ordered by surface temperature O B A F G K M (from hot to cool).
赫罗图
Hertzsprung–Russell Diagram, H–R
A plot of stellar luminosity against temperature (or spectral type) that reveals evolutionary stages. See Stellar physics.
主序
Main Sequence
The principal band on the H–R diagram formed by stars fusing hydrogen in their cores; the Sun lies on it.
角直径
Angular Diameter
The angle an object subtends in the sky, measured in arcminutes or arcseconds; the full Moon is about 31 arcminutes.
The jitter and blurring of star images caused by atmospheric turbulence, measured by the full width at half maximum (FWHM) of the star image in arcseconds; 1″ or better is good, and the finest sites can reach below 0.4″. See Observing conditions.
透明度
Transparency
The clarity with which the atmosphere transmits starlight, affected by clouds, humidity and aerosols, which determines the faintest magnitude visible.
大气消光
Atmospheric Extinction
The dimming of starlight as it is absorbed and scattered passing through the atmosphere, increasing with airmass; more pronounced for low-altitude targets.
气团数
Airmass
A relative measure of the thickness of atmosphere along the line of sight, equal to 1.0 at the zenith and increasing with zenith distance.
闪烁
Scintillation
The rapid fluctuation in a star’s brightness caused by atmospheric turbulence—the naked-eye “twinkling” of stars.
波特尔暗空分级
Bortle Scale
A classification of night-sky light pollution into levels 1–9, with level 1 being an extremely dark pristine sky and level 9 the inner city.
天空背景亮度
Sky Background / SQM
The background brightness of the night sky, often quantified with an SQM (magnitudes per square arcsecond), where larger values mean a darker sky.
暗适应
Dark Adaptation
The process by which the eyes gradually gain sensitivity in darkness, taking about 20–30 minutes. See Visual techniques.
余光视觉
Averted Vision
Observing faint targets with peripheral vision, exploiting the higher sensitivity of the rod cells.
可见性
Visibility / Observability
Whether a target rises high enough at a given time and latitude. See Hemisphere visibility.
The distance over which an optical system brings parallel light to a focus, measured in millimeters, which determines magnification and field of view. See Optics fundamentals.
口径
Aperture
The effective diameter of the primary mirror or objective lens, which determines light-gathering power (proportional to area) and diffraction-limited resolution.
焦比
Focal Ratio, f/
f/ = focal length ÷ aperture; smaller values are “faster” and give higher surface brightness at the same exposure.
视场
Field of View, FoV
The angular extent of sky captured in a single image, determined jointly by focal length and sensor size.
分辨率 / 角分辨率
Resolution / Dawes Limit
The smallest angular separation that can be resolved, limited by diffraction at the aperture; the Dawes limit is about 116″ ÷ aperture(mm).
采样率
Sampling / Image Scale
The arcseconds per pixel, "/px ≈ 206.265 × pixel size(µm) ÷ focal length(mm), which should be matched to the seeing.
出瞳
Exit Pupil
The diameter of the light beam emerging from the eyepiece, exit pupil = aperture ÷ magnification, a key parameter for the visual experience.
赤道仪
Equatorial Mount, EQ
A mount with one axis aligned to the celestial pole, able to track on a single axis to cancel the diurnal motion, suited to long exposures.
经纬仪
Alt-Azimuth Mount, AltAz
A mount that moves about an altitude axis and an azimuth axis, simple in construction but producing field rotation.
极轴校准
Polar Alignment
The process of precisely aligning an equatorial mount’s polar axis with the celestial pole, which directly affects tracking accuracy.
平场镜 / 减焦镜
Flattener / Reducer
An optical accessory that corrects field curvature, or shortens the focal length to widen the field of view and lower the focal ratio.
Two classes of imaging sensor; astronomy today mostly uses CMOS for its low read noise and high frame rate. See Sensors.
单色 / 彩色
Mono / One-Shot Color, OSC
Mono cameras shoot per-channel through filters; color cameras carry a Bayer array and produce color in a single shot.
量子效率
Quantum Efficiency, QE
The fraction of incident photons a sensor converts into electrons, expressed as a percentage; higher is more sensitive.
读出噪声
Read Noise
The inherent number of noise electrons introduced each time a pixel is read out, affecting short exposures and shadow signal-to-noise; lower is better.
增益
Gain
The amplification factor from analog signal to digital value (ADU); raising the gain usually lowers read noise but compresses the dynamic range.
满阱容量
Full Well Capacity
The maximum number of electrons a single pixel can hold before saturation, setting the upper limit of dynamic range.
动态范围
Dynamic Range
The ratio between the brightest and faintest signals that can be recorded simultaneously, often expressed in bits or stops.
暗电流
Dark Current
The flow of thermally excited electrons generated without illumination, increasing with temperature and introducing thermal noise.
制冷
Cooling
Active cooling (commonly stated as ΔT below ambient) to suppress dark current and thermal noise, beneficial for long-exposure deep-sky imaging.
像素尺寸
Pixel Size
The physical edge length of a single pixel (µm), which together with focal length determines the sampling rate.
位深
Bit Depth
The number of bits used to quantize each pixel (e.g., 12/14/16 bit), determining the number of grayscale levels.
A single unstacked raw exposure; many are stacked to improve signal-to-noise. See Deep-sky basics.
总积分时间
Integration Time
The sum of the exposure durations of all usable subframes, often measured in hours for deep-sky imaging.
抖动
Dithering
Slightly shifting the framing between exposures so that hot pixels and fixed-pattern noise are randomized and suppressed during stacking.
跟踪
Tracking
The mount rotating with the celestial diurnal motion so the target stays stationary during the exposure.
导星
Guiding
Using a guide scope or off-axis guider to measure and correct tracking errors in real time, keeping star images round during long exposures.
离轴导星
Off-Axis Guiding, OAG
Splitting off a small beam from the main scope’s light path for guiding, avoiding differential flexure between the main and guide scopes.
幸运成像
Lucky Imaging
Capturing a large number of short frames at high speed and stacking only the best to overcome seeing, commonly used for planets. See Planetary photography.
感兴趣区域
Region of Interest, ROI
Reading out only part of the sensor to increase frame rate, commonly used for planetary and high-speed imaging.
视频堆栈
Video / SER Stacking
The workflow of recording video for planetary imaging, then sorting and stacking frame by frame.
巴特尼夫掩膜
Bahtinov Mask
A tool placed in front of the optics that produces diffraction spikes to aid precise focusing.
Filters that pass only specific emission lines (typical bandwidth 3–12 nm), cutting through light pollution to highlight nebulae. See Narrowband imaging.
Hα
Hydrogen-Alpha
The red emission line of ionized hydrogen (656.3 nm), tracing the main structure of emission nebulae and supernova remnants.
OIII
Oxygen-III
The blue-green emission line of doubly ionized oxygen (about 500.7 nm), prominent in planetary nebulae and hot regions.
SII
Sulfur-II
The deep-red emission line of singly ionized sulfur (about 672 nm), close to Hα and often tracing shock fronts and the outer edges of nebulae.
SHO / HOO
SHO / HOO Palette
Two common palettes mapping narrowband channels to RGB; SHO is the “Hubble palette.”
双窄带
Dual Narrowband
A single filter that passes Hα+OIII simultaneously, suited to color cameras shooting under urban light pollution.
宽带 / RGB
Broadband / RGB
Red, green and blue filters that pass relatively wide bands, used for natural-color imaging.
光害滤镜
Light Pollution Filter
A broadband filter that suppresses the characteristic spectral lines of artificial lighting to improve nebula contrast.
UV/IR 截止
UV/IR Cut
A filter that blocks ultraviolet and infrared to ensure a consistent visible-light focus and accurate color.
A dark (light-blocked) frame at the same temperature, gain and exposure, used to subtract dark-current thermal noise and hot pixels. See Calibration frames.
平场
Flat Frame, Flats
A frame shot under uniform illumination, used to correct vignetting and dust shadows.
偏置场
Bias / Offset Frame
A very short dark frame that records the sensor’s read-out pedestal for subtraction.
暗平场
Flat Dark / Dark Flat
A dark frame at the same exposure time as the flats, used to calibrate the flat frames.
主校准帧
Master Frame
A standard, lower-noise frame produced by combining many calibration frames of the same type.