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Exhibition Guide

Measuring / Exploring the Universe

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Purpose of Exhibition

Celestial objects and various information on astronomy subjects are displayed on the perimeter of this exhibition room. Walking clockwise along the wall, we can travel through the scale of the universe starting from the size of the Earth to the edge of the universe.
This scale is based on the notion of "Powers of Ten (10 no Bekijyo, in Japanese)", making the lengths of each step you take 10 times longer then the last one.
The unit of length at Universe that is used in the exhibition panels, and the way of how distances - like those scales on the wall - are measured, are explained in this exhibition. Planetary systems other than our own solar system and extraterrestrial intelligent life surveys are also introduced.

Additional Knowledge

[Ambiguity of distance to the objects in the Universe]
With the current progress in science and technology, you might think that the distances to objects are exhaustively measured. However, this is not the case. When we measure the distance to the stars, we can perform a triangulation using as a baseline the diameter of the Earth's orbit around the Sun, which is 300 million km. However, because the distances to stars are so far away, even when we want to determine the distance to the nearest star, α(alpha) Centauri in the Centaurus constellation, we have to measure angles smaller than 1" (arc second) or 1/3600 of 1 degree. It becomes even smaller for stars farther away. Another problem to consider is, that when we observe stars from the ground, the atmospheric turbulence makes a difference of 1' (arc second) digit corresponding to 60 times out of 1". Therefore, even with very advanced observation equipment, it is very hard to make observations with high accuracy.
Thus, we started using artificial satellites to measure distances from space, where there is no atmospheric turbulence. Even in this way, only stars located up to distance of around 400 light-years can be observed with good accuracy. There are many stars that are farther than 400 light-years that can be seen with our naked eyes. For example, the distance to Deneb in Cygnus, that forms the Summer Triangle is 1424 light-years away. The two first-magnitude stars in the Orion constellation, the Betelgeuse and Rigel are respectively located 497 light-years and 863 light-years from us. So we need another mothod to make observations for those distant stars. We estimate the distance from their original brightness (absolute magnitude), or also from the temperature and color of that star. Therefore, the distance to the stars might differ depending on which method or model one uses, even though it sholud be the same no matter how and who measures it.
Because of that, the distance to a star might differ from one book to another. There are even cases when the distances to the same star in the same book has changed from a few years ago. As we referred, the absolute magnitude is related with the apparent brightness and the distance. This might be a problem concerning of astronomical objects. For example, the distance to the famous Andromeda galaxy has been referred to as 2.3 million light-years in 2010, but according to recent studies it will become a much bigger value in the future. On the other hand, the size of the Andromeda galaxy is estimated from its apparent size and distance. Here therefore, if the distance became larger, it means that the actual galaxy size also becomes bigger. Since the Universe is too large, even today with advanced measurement technology, there is an ambiguity remained on the distance and size of celestial objects.


【 References 】

Article by Astronomy Section


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