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The Caldwell Objects

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lowing night fell clear, when Herschel returned to<br />

his "potential planet" he discovered that" [t] he<br />

small star is still 1.5 diam. from edge. It has<br />

therefore not moved perceptibly, and is therefore<br />

not a planet." We do not need to be at Herschel's<br />

side to sense his disappointment. It's the feeling<br />

every observer gets after he or she encounters a<br />

strange nebulous glow and believes it might be a<br />

comet — until its true identity as a star cluster or<br />

faraway galaxy is revealed on a star chart.<br />

90<br />

Today we know Herschel's planetary nebula as<br />

NGC 2867, and we know that it is an expanding<br />

shell of gas blown off the surface of a dim and<br />

dying star. NGC 2867 is one of the easiest objects<br />

of its type to spy in the sky. Shining at magnitude<br />

9.7, it is only 0.9 magnitude (roughly a factor of 2)<br />

fainter than M57, the famous Ring Nebula in<br />

Lyra. But NGC 2867 is seven times smaller than<br />

the Ring, so its light is much more concentrated<br />

on the plane of the sky. In fact, the nebula has<br />

such a high surface brightness that it appears<br />

virtually stellar at low powers, a 10th-magnitude<br />

"star" among the multitudes in the rich Carina<br />

Milky Way. <strong>The</strong> object's field is a cinch to locate,<br />

for it lies a little more than 1° northeast of the<br />

2nd-mag-nitude star Iota (ι) Carinae (Aspidiske),<br />

which marks the southeastern arm of the False<br />

Cross. <strong>The</strong> nebula is the center "star" in a 10'-long<br />

chain of three roughly 9th-magnitude, equallyspaced<br />

suns oriented northwest to southeast.<br />

Almost any instrument will show NGC<br />

<strong>The</strong> <strong>Caldwell</strong> <strong>Objects</strong> 355

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