They're light because of the effects of cosmological red shift.

他们质量很轻，这是因为宇宙红移的影响。

There is also the problem that access to telescopes is always at a premium and historically measuring red shifts has been notably costly in telescope time.

使用天文望远镜总是代价很高，在历史上，测量红移要长时间使用天文望远镜，令人注目地花钱很多。