Scientists have been baffled / as weeks and sometimes months have gone by
几个星期甚至几个月过去了,科学家们大惑不解
weeks and sometimes months have gone by/ without a single sunspot,
几个星期甚至几个月过去了,没出现哪怕一个太阳黑点
(如：He had gone two days without online 他两天没上网啦)
a single sunspot 太阳黑点/in what is thought to be 被认为里面有/the deepest solar minimum / for almost 100 years.