What does 则 mean in ...而今年的9月20日则是安室奈美惠40岁的生日? (Let me first write in Mandarin)

关于这个句子：


  据悉，9月16日是安室奈美惠的出道纪念日，而今年的9月20日则是安室奈美惠40岁的生日。


关于“则”的用法，我的词典有这些说明：


rule, standard (noun)
follow an example (verb)
item (measure word)


这些都看来不合适。所这个句子上“则”是什么意思？此外“则”的词性是什么？



(The original sentence in English, in case my Mandarin doesn't make sense)

In the following sentence:


  据悉，9月16日是安室奈美惠的出道纪念日，而今年的9月20日则是安室奈美惠40岁的生日。


In my dictionary, 则 means:


rule, standard (noun)
follow an example (verb)
item (measure word)


All of them seem to be not the case here. So what does 则 mean here and what does it function as (e.g. adverb, noun, verb, etc...)?



Please write an answer in English since I'm not sure if I understand it yet...
则 here, as an adverb, means 'yet'. The structure of 而...则... could be interpreted as 'while'.

So, "而今年的9月20日则是安室奈美惠40岁的生日。" is "while Sep. 20th this year will be the 40th birthday of Anshinaimeihui's."