词条 周年视差
描述: 在一年的时间里，当地球和地球上的所有天文观测者绕太阳运行时，这些观测者的视角会发生变化。与夜空中最遥远的天体作对比，这种视角变化导致了夜空中较近天体的视位置发生改变。这使得这些天体在一年的时间里在夜空中看起来移动在微小的椭圆轨迹上，这种效应被称为周年视差。视运动椭圆的主轴以角度表示，相当于天体（年）视差角的两倍。视差角相当于观测者位置变化一个天文单位（AU），即平均地日距离，或相隔半年的天文观测之间的地球位移的一半。距离单位”parsec“是”秒差距“的缩写，其定义是，对于距离地球1秒差距的恒星，年视差角相当于1角秒。
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其他语言版本
- 阿拉伯语: اختلاف المنظر السنوي
- 德语: Jährliche Parallaxe
- 英语: Annual Parallax
- 西班牙语: Paralaje anual
- 法语: Parallaxe annuelle
- 北印度语: वार्षिक लंबन
- 意大利语: Parallasse annuale
- 日语: 年周視差 (外部链接)
- 韩语: 연주시차
- 巴西葡萄牙语: Paralaxe Anual
- 繁体中文: 週年視差
相关图表
Annual Parallax
图注： Distance determination has historically been a challenge for astronomy. One of the primary ways to measure distance is to use annual parallax. The Earth orbits around the Sun over the course of a year meaning that it moves from one side of the Sun (shown here as position A) to the other side of the Sun (position B) over the course of six months. It then moves back to its original position over the remaining six months. This movement subtly changes the perspective an observer on Earth sees the night sky from. This is similar to the change in viewing perspective you may get when viewing a scene from your left eye and then your right eye. The change of viewing perspective causes nearby objects to shift in position in your vision. The annual motion of the Earth around the Sun changes the perspective of the observer enough to shift the observed positions of celestial objects. How big this effect is depends on the distance to the celestial object. Nearby stars will have bigger shifts in observed position than more distant stars.
The positional shift is known as the trigonometric or annual parallax (which we will call α here) and is defined as the shift in position of a star compared to what an observer at the center of the Solar System (the Sun) would see. In this diagram we see the star viewed from perspectives six months apart (positions A and B). When observed from position A the star’s shift in position will be α while when observed at position B it will be –α. Thus the relative difference in the stars position between being observed at position A and position B will be 2α.
The size of the trigonometric or annual parallax in arcseconds is approximately 1 divided by the distance in parsecs. An arcsecond (often represented by a ″ symbol) is the angular diameter a one-metre-long stick would have when viewed from 206 km away. A parsec (often abbreviated to pc) is 3.26 light years or 30.86 trillion kilometres. This is 206,265 astronomical units (the typical distance between the Earth and the Sun). No other star is closer than 1 pc to the Sun so all stars in the sky have trigonometric parallaxes less than one arcsecond.
While trigonometric parallaxes have long been used to measure the distances to objects in our Solar System or nearby stars, recent advances have pushed the boundaries of these distance measures further. The Gaia satellite has pushed the boundaries of parallax measurements to over a thousand parsecs. Arrays of radio telescopes can also very accurately measure the positions of very distant objects and thus their trigonometric parallax.
Note the Earth and Sun are not to scale here and the Earth’s axial tilt is not accurately represented.
来源： Aneta Margraf/IAU OAE
