Nagoya City Science Museum

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Exhibition Guide





Purpose of Exhibition

Have you noticed the bright stars hanging around the ceiling in this exhibition room? Those are stars making up the "Great Dipper", "Cassiopeia", "Orion", and "Summer Triangle". You cannot see this arrangement if you just look up the ceiling.
There are scopes (round shaped eyeholes) in the astronomical exhibition room, where you can observe each of them from. When you use these scopes, you are looking to those stars in the same relative positions as you will look at them from the solar system, and you will find them forming the constellation.
This exhibition shows that the stars making up the Constellations will change their arrangement depending on the position or direction you look at them, and that those stars that look similar could be in reality really far apart.

Additional Knowledge

[Distance to the Stars and Brightness]
Even if you look at stars with the same actual brightness, they can appear dark when they are far and bright when they are close. Therefore, if you want to compare the actual brightness of stars, you have to convert the brightness to the one as if they were located at the same distance. This converted brightness to compare is called "absolute magnitude" (because it is the absolute brightness), whereas the apparent brightness you will see in the night sky is called "visual magnitude". The distance for comparison is set to 32.6 light years from the Earth, although this looks like a half distance it is a useful number for astronomers.
The distance between the stars and the Earth is so big that we cannot directly measure them. Therefore, as you can see on the chart we measure the distance by triangulation. We use the baseline of 150 million kilometers - the distance from the Earth to the Sun - and measure the apparent changes of position with the angle: θ in the chart. If the distance is 3.26 light years, this angle is equal to 1" (One arc second =1/3600). This angle is what we are acutually measuring, so when we define a standard distance, it is handy to have a round number. However even the closest star, the Centaurs Alpha, is 4.3 light years away. So 3.26 light years, which is 1", is too close to set it as the standard distance. So it was set to "32.6 light years", which is ten times larger.
The absolute magnitude of our sun is 5 magnitudes, which is quite a modest star in our sky.


【 References 】

Article by Astronomy Section


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