日凌，是在春分和秋分太阳穿过地球赤道上空的现象。当此现象发生时，太阳电磁辐射会对地球同步卫星的通讯造成影响，因为地球同步卫星只能定点在赤道上空。受到电磁辐射的影响，透过卫星转播的电视频号会受到干扰，令信号不能接收而出现黑屏，又或信号受干扰而出现雪花。

在北半球，日凌期一般在春分前的二、三月或秋分后的九、十月发生；而在南半球，日凌期在春分后的三月或秋分前的九月发生。在这段期间，太阳、通信卫星与地球的接收点连成一线。由于太阳幅射对整个射电频谱均会影响，包括用于卫星通信的微波波段（C波段、K_u波段和K_a波段）。视乎幅射的强度，可能会增加信号的错误比率，甚或使整段信号不能解读。干扰的时间视乎幅射的强度和持续时间，从12分钟到数天不等。影响日期在春分及秋分点的前后各一个月之内。

A Sun outage, Sun transit or Sun fade is an interruption in or distortion of geostationary satellite signals caused by interference from solar radiation. The effect is due to the Sun's radiation overwhelming the satellite signal.

In the northern hemisphere, sun outages occur before the March equinox (February, March) and after the September equinox (September and October), and in the southern hemisphere the outages occur after the March equinox and before the September equinox. At these times, the apparent path of the Sun across the sky takes it directly behind the line of sight between an Earth station and a satellite. The Sun radiates strongly across the entire spectrum, including the microwave frequencies used to communicate with satellites (C-band, K_u band, and K_a band), so the Sun swamps the signal from the satellite. The effects of a Sun outage range from partial degradation (increase in the error rate) to total destruction of the signal. The effect sweeps from north to south from approximately 20 February to 20 April, and from south to north from approximately 20 August to 20 October, affecting any specific location for less than 12 minutes a day for a few consecutive days.