Yonsei's Korean reader

I've been studying Yonsei University 5-6급 한국어 독본 (Korean Reader). Each reading (they vary from 2-3 pages long to several pages long) is followed by a whole bunch of vocabulary words with English translations.

I wonder how the editors decided which words to give English translations for. In Chapter 6: 까치 ("Magpies") most of the translated words are on the advanced side, but there are some relatively basic words, like 호기심 ("curiosity"). But look at this sentence:

음력 칠월 칠석에 견우와 직녀가 은하수에 걸린 오작교를 건너 일 년에 딱 한 번 만난다는 이야기는 너무나 유명한 전살이다.

My translation, with the help of a dictionary:

There is a very well-known legend that on the seventh day of the seventh month of the lunar calendar, the crow and the magpie are in the Milky Way for Altair and Vega to meet annually.

(...And so on to other astrological matters. I have little confidence that I translated that accurately.)

Does the book offer the English speaker any help translating "Vega" or "Altair" or "Milky Way"? No. Of course, living near the center of a brightly lit city of 11 million people I rather have to take it on faith that Altair and Vega and the Milky Way even exist.

This is a very philosophical set of Korean readings. The first 6 chapters:

1. "Language and Living" by Shim Jae-gi. The author gripes that young Koreans can't speak their own language correctly, says that speaking well is a requisite for thinking well, and quotes Buddha to support his position.

2. "Life's Happiness" by Lee Chang-bae. How to be happy, in the author's opinion.

3. "Meetings"by An Byeong-wook. The author believes in reincarnation, and reflects that the stranger we sit next to on a train may well have repeatedly been our soulmate or good friend in dozens of past lives.

4. "Trees" by Lee Yang-ha. The author imagines trees are sentient and speculates on their personalities, and would like to come back as a tree in a future life.

5. "Life as a Person" by Lee Eo-ryeong. The author compares Korean and Western thought by examining how they cry for help (Koreans say "Save this person!" rather than the egocentric "Help me!").

6. "Magpies" by Oh Chang-yeong. All about magpies in Korean culture and legend.

That last one is the least philosophical one in the bunch (so far). We'll see if the theme continues.