FRED AN­SWERS YOUR QUES­TIONS

Australian Geographic - - Geo Buzz -

Is there any proof the plan­ets and stars in our Galaxy, and the Galaxy itself, has a top and bot­tom? Is it not that early writ­ers came to this con­clu­sion be­cause the world, as known to them, was the North­ern Hemi­sphere? Also, I’ve al­ways been led to be­lieve the Galaxy is a hor­i­zon­tal plane in space. Could it not be ver­ti­cal, for in­stance? John Wil­liams, Creswick, VIC

You’re quite right: what is ‘up’ in a cos­mic sense is ar­bi­trary, and the dom­i­nance of north as a pre­ferred di­rec­tion is be­cause most peo­ple live in the North­ern Hemi­sphere. On the largest scale, the Uni­verse is the same in all di­rec­tions, so there’s no pre­ferred di­rec­tion. You’re also right that the disc of our Galaxy is tilted al­most at right an­gles to the plane of the So­lar Sys­tem (the eclip­tic), and at about 63 de­grees to the plane of Earth’s equa­tor. If you have a space ques­tion for Fred, email it to ed­i­to­rial@aus­geo.com.au

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