Hunting Down the Helix
Also known as NGC 7293 and Caldwell 63, the Helix Nebula in Aquarius is one of the nearest and brightest of the class of objects known as planetary nebulae. A planetary nebula is born of an aging star that exhausts its nuclear fuel and sheds its outer layers into space. As the nebula expands, the core of the star is exposed. This hot, dense cinder will evolve into a white-dwarf star and then slowly cool over billions of years.
Observationally, the Helix is one of the easiest of bright planetaries and one of the most elusive. It can be seen in binoculars and yet remain invisible in large telescopes. These claims may seem contradictory, but they can be explained by the nebula’s low surface brightness. If the light of the Helix were gathered into a single point, it would shine with the light of a 7.3-magnitude star. But this light is spread over a rather large area of the sky with about half the angular diameter of the Moon! Low powers will help concentrate the nebula’s light, and wide fields will show plenty of surrounding dark sky for contrast. That’s why the Helix is a good small-scope target.
With such an elusive quarry, you need to hunt the Helix carefully being sure that your scope is aimed at the correct spot in the sky. The Helix is never very high in the sky from my semirural site in upstate New York, but I can sometimes see an adjacent star, Upsilon (υ) Aquarii, with the unaided eye. Spotting Upsilon will make your nebula search simple. But if your sky is too bright to show that star, try starting at 3.3-magnitude Delta (δ) Aquarii. From Delta, look 4° southwest for 4.7-magnitude 66 Aquarii. It should fit in the same finder field with Delta and shine with an orangish light through the telescope. Continue along that line another 2.8° and you will come to yellow-white Upsilon, the brightest star in the area at magnitude 5.2. The Helix sits 1.2° west of Upsilon and is best sought with a low-power eyepiece. Two 10th-magnitude stars lie halfway between, helping pinpoint the Helix in two easy jumps.
I can pick out the Helix with 50-millimeter binoculars from home. At first glance a small telescope shows only a featureless oval disk, but keep looking. The Helix Nebula yields up its details only to the patient observer.