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News has come up lately about the impending approach of asteroid 2017 VR12 and how it might be visible to some backyard telescopes. However I've read conflicting or vague reports on what kinds of telescopes will be powerful enough to spot it.

I've got a modest but still decent little Celestron NexStar 4 SE, which is a 4" Schmidt-Cassegrain. Can anyone say for sure whether that has the power to see the asteroid? Currently I just have the stock eyepiece. Would I need to get a better one to help out?

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2017 VR12 is expected to reach magnitude 11.8 on the night of March 6-7. This is near the limit of a 4-inch scope; actual visibility depends on your observing site, your eyes, and the magnification. You can get a more definite answer by trying to see stars of similar magnitude.

The other hard part is to acquire the target. It will look like a star, so you need a finder chart showing stars at least as faint as the asteroid. If you haven't observed one before, try finding a named asteroid around magnitude 10 first. In this close approach, 2017 VR12 will move 0.9 degree per hour north-south, fast enough that you need either quarter-hour marks plotted on the finder chart or a continuously updated display.

Stellarium works pretty well for me; I downloaded some of the extra star catalogs, and I import the latest available orbital elements for the asteroid of interest. If you wish to use your scope's go-to capability, this guide may help, but you still have to figure out which "star" in the eyepiece field is the asteroid. This article identifies a few brighter stars you can try to watch it pass.

I do recommend getting a ~10mm eyepiece in addition to the 25mm one you have. It might help you see stars half a magnitude fainter, but the main benefit is higher magnification for planets.

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    $\begingroup$ Possibly moving fairly fast considering, so the finder chart should have ticks hourly or better, and attention to time zone... Consider adding something from earthsky.org/space/asteroid-2017-vr12-closest-march-6-7-2018 $\endgroup$
    – uhoh
    Commented Feb 20, 2018 at 12:47
  • $\begingroup$ Whether it is visible will also depend on where you are located. I think you would need to be a long way from cities and street light to see this in a 4” scope. Even if you can see it, it will not be impressive. $\endgroup$
    – Dr Chuck
    Commented Feb 20, 2018 at 21:55
  • $\begingroup$ Yikes! I didn't know it would be that fast! $\endgroup$
    – uhoh
    Commented Feb 21, 2018 at 6:03
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    $\begingroup$ This is exactly the kind of succinct and practical advice I was looking for. Thank you! I just ordered an eyepiece kit that has an 8mm and 12mm so I'll experiment with those in the meantime and try to track other objects of a similar magnitude. $\endgroup$
    – thanby
    Commented Feb 21, 2018 at 14:40

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