The Caldwell Objects

74
are 0.8 x 0.5 light-year. Its gases
are expanding away from the
central star at a speed of 14 km
per second.
NGC 3132 lies in a rather
remote section of Vela, just
south of its border with the
dim constellation Antlia, the
Air Pump. If you live at a
southerly locale and have a dark sky, finding the
nebula will not be a problem. Start at 2ndmagnitude
Lambda (λ) Velorum. A little more
than 12° east-northeast of Lambda Velorum is
magnitude-3.8 q Velorum, which forms the
southwestern corner of a 2°-long equilateral
triangle with a 5th- and a 6th-magnitude star.
(Confirm this with your binoculars.) NGC 3132 is
2¼° northwest of q Velorum and 1¼° west (and
ever so slightly south) of the triangle's northern
star.
If your skies are not that great, or if the
object is low to the horizon, you can find the
planetary with an equatorial mount. First locate
2nd-magnitude Zeta (ζ) Puppis with a wide-field
eyepiece and center it in your scope. Zeta is at -
40° exactly, so all you have to do is use your
setting circles to move your telescope 26.2' south
and 2 h 3 m east of Zeta Puppis. The planetary
should be obvious. At 23x in the 4-inch NGC
3132 looks like a 9th-magnitude star and
warrants immediate attention at higher powers.
Several sources claim the plan-etary's visual
brightness is magnitude 8.2. But
this is not true. The error can be traced to Robert
Burnham Jr.'s Celestial Handbook, which failed to
clarify that 8.2 was the nebula's photographic
magnitude; NGC 3132's apparent visual
brightness is a full magnitude fainter. (This is
precisely the opposite of what one might expect.
But there is a reason for this. To show the
nebula's faint features, photographic exposures
had to be long, and hence they would overexpose
NGC 3132's bright central star, exaggerating the
nebula's total brightness. The same problem can
be seen in NGC 246, which has three stars
superimposed on its nebulosity.) This error has
led others to assume that the planetary is brighter
than it truly is. Most plausible published
magnitudes range from 9.2 to 9.7. I observed
NGC 3132 in April 1997 using 7x50 binoculars
and, blissfully unaware of the controversy, I
made an independent visual estimate of
magnitude 9.2.
Not much is gained by boosting the magnification
of the 4-inch to 72x, though the nebula's
nature is clearly revealed by a slightly swollen
body like a star just out of focus. With a pro-
294 Deep-Sky Companions: The Caldwell Objects