How big will Apophis appear in the sky at its closest point of approach in 2029? Will it compare to the moon? How long will it linger as it passes?
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2According to https://en.wikipedia.org/wiki/99942_Apophis#Physical_characteristics it will peak at magnitude 3.4, so only as bright as an average star. More details: http://newton.dm.unipi.it/neodys/index.php?pc=1.1.3.1&n=99942&oc=500&y0=2029&m0=4&d0=13&h0=18&mi0=0&y1=2029&m1=4&d1=14&h1=0&mi1=0&ti=10&tiu=minutes – Apr 26 '16 at 04:27
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Current estimates put Apophis's diameter around 325 m and its 2029-04-13 approach about 38000 km from the center of the Earth. I figure an angular size <= 2 arcsec, almost starlike even if you manage to track it in a telescope. Ephemerides show it at apparent magnitude 3.5 or so just before closest approach - visible but not outstanding to the unaided eye at night - and spending about 36 hours within 1 lunar distance of the Earth.
Mike G
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I'm not sure if the Hubble telescope will be operational then, but it would be a few dozen pixels wide at that size and so nicely imageable in visible light. fyi I've just asked Has Hubble ever been used to try to image a near Earth asteroid? – uhoh Jun 23 '19 at 02:17