Meaning of 春うらら

Question

I was reading this Haiku behind a tea bag:

恋愛の

方程式解く

春うらら

I actually have to questions:

1. Why is it considered a haiku although the second verse has actually 8 syllables? In my understanding, except in some cases.
2. What is a good way to explain in English 春うらら? It is not in my dictionary and it seems to be a word expressing some sort of special feeling related to spring. I asked a couple of Japanese people and I get the overall idea but none of them seemed to be able to give a clear explanation.

Edit: answer to 1.

I think this pretty much answers question 1. Is this one of such cases? From wikipedia:

韻律[編集]

俳句は定型詩であり、五・七・五の韻律が重要な要素となっている。この韻律は開音節という日本語の特質から必然的に成立したリズムであって、俳句の制約とか、規則と考えるべきではない。五の部分が6音以上に、または七の部分が8音以上になることを字余りという。

Answer 1

実用日本語表現辞典 explains 春うらら as:

春うらら　春のうららかな様子。明るく朗らかで、の‌​‌​どかなさま。

明鏡国語辞典 explains うらら as:

う‌​らら【麗ら】〘形容動詞‌​〙うららか。『うららに照る日』『春のうら‌​らの隅田川〈花〉』

and うららか as:

​うららか【麗‌​らか】〘形容動詞〙①空が明るく‌​晴れて‌​日がのどかに照っているさま。うらら‌​。‌​『うららかな日和』

I think 春うらら is a word that describes... a sunny, clear, bright, mild, lovely, happy, and peaceful spring day.

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I see that you've already found the answer to your first question. Yes, it's [字]{じ}[余]{あま}り.

Answer 2

To answer to 1, yes, you're right. It's an exception, "字余り." There're many haiku with extreme exceptions called "free-style haiku." Here's a famous one.

せきをしてもひとり ---尾崎 秀雄(Housai Ozaki)

I think it's no longer haiku, but it's haiku. According to Japanese wiki, when an author makes free-style haiku, the author has intention to make it free from fixed-style. The problem the short poem is either haiku or not depends on what auther intended to make. https://ja.wikipedia.org/wiki/自由律俳句

And "うらら" has its original form, "うらうら." https://kotobank.jp/word/%E3%81%86%E3%82%89%E3%81%86%E3%82%89-441734

So, it could be translated into English like: "daintiness of spring"