top of page

Let's enjoy the starry sky

Kitakaruizawa is a place where you can see the stars very beautifully.

The reason is that it is far from the city and there are few lights, and the altitude is high and the air is clear.

This is a summary of the knowledge of the starry sky that even beginners can enjoy. Please enjoy

star brightness

You may have heard the term “first class star”.

Stars are grouped by brightness, the brightest stars are called 1st magnitude stars, and the barely visible stars are called 6th magnitude stars. The smaller the number, the brighter it is. There are only 21 1st magnitude stars in the sky, and they are 100 times brighter than 6th magnitude stars. In the past, the 1st magnitude star was thought to be the brightest, but a brighter star was discovered, and it began to be written as a negative value. By the way, the sun is -26.7 magnitude, the moon is -12.7 magnitude at full moon, Venus is -4 magnitude, and Jupiter, Mars, and Mercury change depending on the distance from the earth, but when it is close to the earth, it is -3 magnitude. It is said So, if you think "that star is bright", there is a high possibility that it is one of these stars or a star of the first magnitude. It is also said that the stars are beautiful in winter. The reason for this is partly because the air is clear, but partly because it's the season when you can see 7 out of 21 bright first-magnitude stars.


star color

If you look closely at the stars, you can see that there are red, blue, and yellowish ones.

This is due to the difference in the temperature of the stars. The hot part of fire is blue in the center, and the outer part is red because the temperature is low. A hot star has a surface temperature of nearly 40,000 degrees and appears bluish-white. As the temperature drops, the color changes to white, yellow, orange, and red.By the way, the surface temperature of the sun is about 6000 degrees, so it looks yellow.

You can also guess the age of a star by its color. Stars get cooler and redder as they age. Conversely, bluish stars are young stars that were born relatively recently. The younger you are, the hotter you burn. You may be with humans.



star distance

Have you ever heard the term “light year”?

Nothing in space travels faster than light, which travels 300,000 kilometers per second (7.5 times around the Earth). The universe is so vast that it takes years for even light to reach us, so we use "light years" to express the distance of the universe. A light year is the distance light travels in one year, which is 9.5 trillion kilometers. By the way, the distance from the moon to the earth is about 380,000 kilometers (1.3 light seconds), and the distance from the sun to the earth is about 150 million kilometers (8 light minutes). So we see the moon 1.3 seconds ago and the sun 8 minutes ago. By the way, the farthest star we could observe is Icarus, which is 9.4 billion light years away from Earth. The closer the star, the brighter it is, and the farther away it is, the darker or invisible it is. If all the stars are arranged at the same distance, it may become a completely different starry sky.


​Let's find a planet

If you are interested in stars, try looking for planets.

​The planets, as they say, are wandering stars, move steadily and appear in various places.

​Other stars appear to flicker, but the following planets have strong light and appear to shine continuously.

We will introduce planets that are easy to find and tips on how to find them, so please try to find them.


・There are words such as the evening star and the morning star, but the star that shines brightest in the evening or at dawn is Venus.
・You can't see Venus at midnight

・If there is a bright star in the western sky after sunset or in the eastern sky before sunrise, it is Venus (a star of -4 magnitude).

・ Stars of -2nd to -3rd magnitude are very bright and appear to shine gold

Venus is called the evening star or morning star, while Jupiter is called the "midnight star" because it can be seen at midnight.

・The location changes every second depending on the date and time. Please check the position on the "National Astronomical Observatory of Japan website"​


・Mars is a bright red star in the night sky.
・Because Mars changes its distance from the Earth, its brightness changes to -2 magnitude when it is close and 2 magnitude when it is far away.
・It approaches the Earth every 2 years and 2 months, and will be closest to the Earth in December 2022, and will remain bright until around March 2023.

・The next approach will be around February 2025.


・Saturn is a bright star that shines with a dull yellow color (0 magnitude star).
・The light is strong, and the twinkling that flickers is considerably less than other stars

・The location changes every second depending on the date and time. Please check the position on the "National Astronomical Observatory of Japan website"​

spring constellations
(Representative is the Big Dipper)


summer constellations
(Representative is the Summer Triangle)


autumn constellations
(Representative: Cassiopeia)


​​winter constellations
(Representative is Orion)



bottom of page