The Local Universe

I just stumbled across this on Amanda Bauer’s blog  and thought I’d post it here because it’s so nice. The film is by Hélène Courtois, Daniel Pomarède, R. Brent Tully, Yehuda Hoffman, and Denis Courtois and it describes the Cosmography – like geography, only more cosmic – of the Local Universe. I’m not sure there’s a consensus among cosmologists about what exactly “local” means, but I’d say it probably means out to a few hundred Megaparsecs from the observer (say up to about a billion light years) or, alternatively, with redshifts much less than unity.  That may not sound very nearby at all, but even on such scales the look-back time is sufficiently short that the effect of cosmic evolution and/or the expansion of the Universe is negligible, so when we look at objects at such distances we’re seeing them as they are “now” rather than as they were in the past, which is the case when we study extremely distant objects.

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