大熊座

As we recall from the last article, I'm gonna introduce a mathematical way to recognize the Big Dipper.

First let's learn something about the measurement scale of daily astronomical observations.We have 360 degrees at most when we look up into the night sky. It is understandable. Now, straighten your arms and as you can see, the width of your little fingernail equals to 1 degree. Based on this, the width of your three fingers equals to some 5 degrees. The seven stars which consist the Big Dipper are α, β, γ, δ, ε, ζ and η, respectively. The details are as follows.

The distance between α and β is around 5 degrees.

The distance between α and δ is about 10 degrees.

The vertical distance between α and η is about 25 degrees.

It seems to me that the intuitive way is simple enough. Anyway, what I have explained just now would be of great help in our future learning.

Now let's have a look at the Ursa Major.

The Ursa Marjor is the most famous and brightest constellation through all year. While among the four seasons, Spring is the best time to observe it. Once we point out the location of the Big Dipper, the whole Ursa Marjor is easily to recognize. Because the Big Dipper is the tail of the big bear in the sky.

There is a famous Greek mythology about the Ursa Marjor. Once a beautiful girl named Calisto was a hunter. She followed the Luna Artemis all day to hunt animals. She was the most beautiful girl among the girls who hunted with Artemis. One day she went hunting as usual. When she got to a very desolate place, she felt sleepy. So she took a nap. At the same time, Zeus saw everything in the sky. He was fascinated with Calisto's appearance. Then he came down from the sky and turned his appearance into Artemis. He approached Calisto when she just woke up. Calisto thought it was her beloved Luna Artemis. So she was very happy. All of a sudden, Zeus turned his appearance back and raped Calisto. What a tragedy. But it didn't end like this good.

After Zeus left, Calisto was so ashamed and desperate though it was not her fault at all. She seldom talked to her sisters and liked to be alone. When she hunted, she was not as brave and agile as she used to be. Months later, her pregnancy was found by Artemis and everyone else. They didn't know the truth because they were never told. Artemis was so furious that she drove Calisto out of her place.

Calisto had to leave and found a grass sheild in the wild. Soon she gave birth to a beautiful boy named Acas(Ursa Minor 小熊座). Though life was hard on them, she felt happy with her little child.

Until the wife of Zeus, Hera found about this. She was extremely jealousy of Calisto's beauty and so mad at her husband's affair so she turned Calisto into a big bear. What a tragedy. But it didn't end like this good.

Calisto, once a great and beautiful hunter, lived as a bear for fifteen years, away from her beloved son. One day Hera found out Calisto's son had become a handsome man. She was jealousy again. An evil idea occured to her.

She made Acas come across his mother when he was hunting. Calisto was very excited and happy when she saw her son. She forgot she was a bear and her son was a hunter. It seemed that Acas's gonna kill his missed mother! What a tragedy! But it didn't end like this terrible.

Zeus could not bear that his son Acas killed his own mother. So he turned Acas into a little bear. As Acas became a bear, he recognized his mother immediatly. And they huged each other with happiness.

Hera would not let go of them. So she ordered a hunter(Bootes 牧夫座) with two hunt dogs（Canes Venatici 猎犬座） to chase them all the year.

Well, the story doesn't end here. But I'm afriad I have to tell you the rest of it next time. Good day!