# 托福TPO-42 Lecture 2-3

Is that the same as density?

That’s right. Both richness and density refer to the number per area.

Rich clusters, or dense clusters, contain a relatively high number of galaxies.

And symmetry just refers to its shape?

Roughly speaking, yes.

Whether the shape of the cluster was the same on the left side as on the right side.

So Abell used categories like that to classify clusters on a scale: from regular to irregular.

A regular cluster is sphere shaped, symmetrical, and most dense in the middle,

the greatest number of galaxies concentrated in the middle of the cluster.

And irregular cluster might appear to be lopsided, asymmetrical, with a little concentration of galaxies in the center.

 重点单词 查看全部解释 density ['densiti] 想一想再看 n. 密集，密度，透明度 irregular [i'regjulə] 想一想再看 n. 不合规格之物adj. 不规则的，不整齐 联想记忆 concentration [.kɔnsen'treiʃən] 想一想再看 n. 集中，专心，浓度 scale [skeil] 想一想再看 n. 鳞，刻度，衡量，数值范围v. 依比例决 classify ['klæsifai] 想一想再看 vt. 分类，归类 联想记忆 symmetrical [si'metrikəl] 想一想再看 adj. 对称的 联想记忆 symmetry ['simitri] 想一想再看 n. 对称(性), 匀称，整齐 联想记忆 contain [kən'tein] 想一想再看 vt. 包含，容纳，克制，抑制vi. 自制 联想记忆 concentrated ['kɔnsentreitid] 想一想再看 adj. 全神贯注的，浓缩的 动词concentrate asymmetrical [.eisi'metrikl] 想一想再看 adj. 不对称的，不均匀的
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• 托福TPO-42 Lecture 2-1 2016-09-30
• 托福TPO-42 Lecture 2-2 2016-10-01
• 托福TPO-42 Lecture 2-4 2016-10-03
• 托福TPO-42 Lecture 2-5 2016-10-04
• 托福TPO-42 Conversation 2-1 2016-10-10
• 关键字： 练习 训练 听写 托福 TPO

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