Mars and Earth have orbits which change with time.
火星和地球的轨道随着时间而发生改变。
In molecular orbital theory, we named orbits based on their symmetry.
在分子轨道理论中，我们基于轨道的对称性给它们命名。
Most known extrasolar planets reside in highly elongated, not circular, orbits.
大多数已知的太阳系外行星都居住在高度拉长而非圆形的轨道上。
They will likely then travel close enough to neighboring planets to disturb their orbits also.
然后，它们很可能会飞得离邻近的行星足够近，从而扰乱它们的轨道。
Let's continue our discussion now by talking about orbits, especially those of the so-called periodic-orbit comets.
现在我们继续讨论，谈谈轨道，特别是那些所谓的周期轨道彗星。
Astronomers suspect that pairs of planets also engage in this slingshot activity, leaving them in disturbed, elliptical orbits.
天文学家怀疑成对的行星也参与了这种弹弓活动，使它们处于不规则的椭圆轨道上。
In any given year, about a dozen known comets come close to the sun in their orbits, the average person can't see them all, of course.
在任何一年中，大约有十几颗已知的彗星在其轨道中接近太阳。当然，一般人看不到所有的彗星。
The orbits of Mercury, Venus, Earth, Mars, Jupiter and Saturn fit neatly into this pattern; Uranus, discovered in 1781, also obeyed the law.
水星、金星、地球、火星、木星和土星的轨道恰好符合这种模式；1781年发现的天王星也同样符合该定律。
Comets formed in circular orbits but were gravitationally flung into their present-day elliptical orbits when they ventured too close to planets.
彗星在圆形轨道上形成，但当它们冒险太接近行星时，就会被引力抛入现在的椭圆轨道。
They can attain more distant orbits; NASA plans for most of its future earth escaping payloads (to the moon and Mars especially) to carry CubeSats.
它们可以到达更远的轨道；美国国家航空航天局计划在其未来的大部分发射任务（尤其是去月球和火星的）中携带立方体卫星。
The nearly circular orbits of planets in our solar system led scientists to expect that planets around other stars would also reside in circular orbits.
在我们的太阳系中，行星的轨道几乎是圆形的，这使得科学家们预测，其他恒星周围的行星也会位于圆形轨道上。
The Earth orbits in an ellipse.
地球沿椭圆形轨道运动。
Mars orbits the Sun in 687 days, which means 1 Earth year on Mars is 687 days.
火星绕太阳公转的周期是687天，这意味着火星上的1个地球年是687天。
As Europa orbits its planet, however, it flexes due to the gravitational tug-of-war between it, its sister moons, and Jupiter.
然而，当木卫二绕其行星运行时，由于姊妹卫星和木星之间的引力拉锯战，它会弯曲。
The most complex engineering project ever attempted has created an enormous set of interlinked modules that orbits the planet at more than 27,000 kilometres per hour.
有史以来最为复杂的工程项目创造了一组巨大的相互连接的模块，其以每小时27000公里的速度绕地球运行。
So, orbits in general are ellipses.
所以，轨道总体上说是椭圆的。
但大部分轨道不会。
它绕着一颗红矮星运行。
Now, circular orbits are special.
圆形轨道非常特殊。
Let's pursue the idea of circular orbits.
我们用圆轨道的概念。
In comparison, the Earth orbits at just 1 AU.
相比之下，地球轨道只是一个天文单位。
The planets occupy regular orbits in the space.
行星运行的轨道空间位置是有一定规则的。
He concluded that the earth orbits the sun.
笛卡尔也总结出地球是绕着太阳转的。
Some take only a few years to complete their orbits.
其中一些恒星仅需几年时间就能完成一周的运行。
Dr Bottke has been tracking the orbits of asteroids.
伯克(Bottke)博士一直在追踪小行星的运行轨迹。
Orbits were not the sedate, orderly system they are today.
轨道还不是今天那样静止、有序的系统。
In the past, information about orbits was a closely guarded secret.
在过去，关于轨道的信息是严格警戒的秘密。
It doesn't simply orbit the nucleus, but as it orbits it spins.
它并不只是简单地绕原子核旋转，而是同时进行公转和自旋。
The orbits around the Earth are too valuable to let this happen.
绕地球的轨道太有价值而不能让这些发生。
Well, the planet orbits around the sun -- -- in some trajectory.
行星以某轨迹绕太阳运行。
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