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Tuesday, August 29, 2017


Seeing NEO 3122 Florence from Australia

NEO 3122 Florence as seen from Adelaide on 1 September at 23:24 when the asteroid is highest in the sky (similar views will be seen from other Australian locations at an equivalent local time. click to embiggen).

NEO 3122 Florence makes an historic approach to Earth in early September. This will be the closest this asteroid, named after reforming nurse Florence Nightingale has come since 1890.

While not a particularly close approach (September 1, 12:06 UT, 0.047 AU, around 18 Earth-Moon distances), this will be the closest a large NEO has come to Earth since this class of objects were first described.

With a diameter of about 4.3 km, Florence ranks fourth in diameter of those NEO's classified as potentially hazardous. It is also the brightest of the Large NEO's, brighter than 3200 Phaeton (the asteroid responsible for the Geminid meteor shower).

Printable black and white chart showing the track of 3122 Florence from the 28th on. The Asteroid passes from close to Grus the crane, through and southern skies passing through Capricornius and Delphinus then Cygnus (click to embiggen and print)

The asteroid will range from magnitude 9 up to around magnitude 8.7 then fading down to 10.

This means that the asteroid is potentially viewable in good binoculars (10x50's and up) under dark sky conditions.  However, the waxing Moon will make binocular detection harder closer to closest approach. It will remain easily visible in small telescopes even with the increasing moonlight.

Printable black and white chart  suitable for binoculars showing the track of 3122 Florence from the 1st, the large circle is the field of view of 10x50 binoculars, (click to embiggen and print)

Although the asteroid is effectively on a line between the bright stars Fomalhaut and Altair, Finding the asteroid can be a bit tricky without good maps.

On the 29th, the asteroid is 22" from Zeta (ζ) Capricorii, and so should be easy to spot. You will need to watch the stars around  Zeta for around 15 minutes to detect the movement of Florence.

On the 30 the brightening Florence is within 22' of 29 Capricorii (which forms a triangle with iota and theta Capricornii), again, watching for 10-15 minutes will detect the asteroid drifting. 

On the 31st the asteroid is between mu and beta Aquarii, but is not close to a useful guide star.

Printable black and white chart  suitable for telescope showing the track of 3122 Florence from the 1st, tthe large circle is the field of view of 10x50 binoculars, he small circle is the field of view of a 23 mm eyepiece and a 114 mm refractor.(click to embiggen and print)

On the first the asteroid is within binocular distance of alpha Equuleus, and between that and 1 Aquarii, but again is not near any obvious guide star. Still if you watch for 10-15 minutes you will see the asteroid drift against the background stars.

Many instruments will be watching this approach, including the Goldstone radar to try and capture its shape and possible satellites.

While not spectacular, this will be an historic pass to witness, the next closest approach of Florence is in 2057.

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This was very helpful thank you. Especailly for someone who is not familiar with observing the night sky.
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