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Grade 4 (age 9-10)

grade 4 Stars and Constellations

Look up at the night sky from the countryside, away from lights, and a few especially bright stars stand out among countless others. People long ago joined bright stars with lines, imagined shapes such as a ladle, a hunter, or a queen, and gave them names; these are constellations. Constellations are also guides: follow the ladle-shaped Big Dipper and you can find the North Star, which always sits in the northern sky. Compare the shapes of three constellations with the buttons, and in the lower picture sort star brightness from 1st to 6th magnitude.

Constellations in the night sky

✨ What is a constellation?
①A constellation is a shape such as a person, animal, or object imagined by joining bright stars with lines
②The stars in a constellation are actually at very different distances from Earth
③Different constellations show up in the evening in each season; Orion is easy to see in winter
④The Big Dipper and Cassiopeia are guides to finding the North Star
⑤Orion's upper-left star is reddish and its lower-right star bluish, so stars differ in colour too

How bright stars are

💡 How bright stars are
①Star brightness is given as a magnitude
②The smaller the number, the brighter the star, so a 1st-magnitude star is much brighter than a 6th-magnitude one
③With the naked eye you can see stars down to about 6th magnitude
④The North Star is only about 2nd magnitude, not the brightest star, but it guides us because it always stays in the north
⑤A star's colour is linked to its surface temperature, so blue stars are hotter than red ones

Summary

Constellations
Constellation = shape made by joining bright stars with lines
Different constellations appear in the evening sky in each season
Finding the North Star
Distance between the Big Dipper's two end stars × 5 → North Star
The North Star always sits in the northern sky and shows us direction
🎯 Key points
①A constellation is a shape made by joining bright stars
②The Big Dipper is ladle-shaped, and its two end stars lead to the North Star
③Cassiopeia is W-shaped and can be seen all year
④The smaller the magnitude number, the brighter the star
⑤A star's colour depends on its temperature, and blue stars are the hottest

Examples and Unit Test

Example 1
Which is brighter, a 1st-magnitude star or a 6th-magnitude star?
1
Star brightness is given as a magnitude, and the smaller the number, the brighter the star.
2
A 1st-magnitude star has a small number and is bright, while a 6th-magnitude star is a dim star you can barely see with the naked eye.
▸ The 1st-magnitude star (a smaller number means brighter)
A 1st-magnitude star is about 100 times brighter than a 6th-magnitude star.
Example 2
How can you use the Big Dipper to find the star that shows direction?
1
The Big Dipper is a ladle-shaped group of stars that guides you to the North Star.
2
Stretch the distance between the two end stars of the bowl about 5 times, out from the open side of the bowl, and you reach the North Star.
▸ Stretch the gap between the two end stars about 5 times to reach the North Star
Choose the Big Dipper in the first picture and a dotted line runs from its two end stars to the North Star.
Unit-test style
Which statement about stars and constellations is correct?
①A 6th-magnitude star is brighter than a 1st-magnitude star
②The North Star always stays in the north and shows direction
③Constellations look exactly the same in every season
④All stars are the same colour
⑤The stars in a constellation are actually touching each other
▸ ② The North Star always stays in the north and shows direction
1
The North Star always sits in the northern sky, so it helps us find direction.
2
1st magnitude is brighter than 6th (①), different constellations show up in each season (③), star colours vary with temperature (④), and the stars in a constellation are at different distances from Earth (⑤).
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