That is to say, intervals between observation periods could vary-some longer, others shorter.

也就是说，观察时间段之间的间隔可能会不一样，有些长些，有些短些。

The first observation period could begin at 9 am, the second at 10 am and so forth.

第一个观察时间段可以从上午9点开始，第二个在上午10点开始，以此类推。

However, calculating how many there are using long period comet observations, you wind up getting about 400 billion.

然而，如果用长周期彗星观测来计算有多少彗星，你最终会得到大约4000亿颗的答案。

Those staying at home within the observation period are required to report their health conditions to their communities regularly.

观察期内，居家旅客要定期向所在社区报告健康状况。

Others require two physicians to perform the test, with an observation period in between.

其他人需要两名医生进行测试，中间有观察期。

The observation period, however, ended before they could see the moon complete its path. To confirm the existence of the moon, the astronomers hope to observe the star again next spring.

但是在观察到这颗月球完整的运行路径之前，观察期就结束了。为证实这颗月球的存在，天文学家希望能在明年春天再次观测这颗恒星。