Measuring the Universe
May 30, 2012 7:05 AM   Subscribe

The Royal Observatory, Greenwich has put together the fantastic short video Measuring the Universe which briefly describes the different techniques used to allow us to calculate the vast distances to stellar objects in space. [via]
posted by quin (11 comments total) 25 users marked this as a favorite
Really interesting and well put together.
posted by pez_LPhiE at 7:26 AM on May 30, 2012

Thanks! Just the sort of perfect concise explanation to send to people who have wondered about this.

It seems like ones with similar conception could be put together for how we know the size and mass of the Earth, the Earth/Sun distance etc.
posted by vacapinta at 7:42 AM on May 30, 2012

They had me up to where they compared the light from coming from stars to a 40W incandescent lightbulb. As if future generations will have any idea what this is.
posted by three blind mice at 7:46 AM on May 30, 2012 [1 favorite]

I don't think they made this video as a monument to the ages.
posted by invitapriore at 8:35 AM on May 30, 2012

The one thing that I do think makes this inappropriate for children is the expanding ruler illustration to demonstrate the expansion of space, which I found unreasonably terrifying as an adult.
posted by invitapriore at 8:40 AM on May 30, 2012

That was cool, thanks.
posted by yoink at 8:46 AM on May 30, 2012

As an interesting aside: it's pretty easy to use this sort of cosmic distance ladder to measure everything in terms of "astronomical units", where 1 AU is the radius of Earth's orbit. But how do you determine how far away the Earth is from the Sun, in kilometers? For a car driving down the road, like in the video, you can just measure how many times your wheels turn; but you can't exactly put down a tape measure or a measuring wheel between Earth's position in space now and its position in December.

The answer: observe the transit of Venus, the same type of event that's coming up next week. The 1769 transit of Venus was the subject of a major scientific undertaking in order to get precise enough measurements to actually determine the absolute size of the astronomical unit. Nowadays this method has been superceded by the use of radar measurements, but it's still a neat little historical connection.
posted by Johnny Assay at 9:22 AM on May 30, 2012

If space in the universe is expanding, are we getting smaller?
posted by stbalbach at 9:26 AM on May 30, 2012

Next they should do a video showing how to make the Kessel run in under 12 parsecs.
posted by yoink at 9:43 AM on May 30, 2012

Johnny Assay: that's exactly why they've made this video now. See the text under the video about the exhibition it's part of.
posted by edd at 9:55 AM on May 30, 2012

stbalbach: Yes and no. If you use a ruler that expands with the Universe (measuring space in what cosmologists call 'comoving coordinates') then yes, you get smaller compared to that ruler with time.

However, if you use meters, say, or the wavelength of light of some specific frequency, or something along those lines to define the size of your ruler, we stay the same size. Cosmologists call that system 'physical coordinates'.

Basically, as the universe expands, well-separated galaxies will retain constant positions in comoving coordinates, but systems bound together by gravity or other forces (e.g. our own Milky Way, or the atoms in your body) will not grow (the jargon is that they have 'broken away' from the expansion of the universe) and stay a constant size in physical coordinates.
posted by janewman at 12:15 PM on May 30, 2012

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