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Cosmic Challenge: NGC 1535


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Cosmic Challenge:
January 2020

NGC 1535

 

Phil Harrington

 

This month's suggested aperture range:

Giant binoculars (70mm and larger)

2- to 5-inch (50-127mm) telescopes

 

 

Target

Type

RA

DEC

Constellation

Mag

Size

NGC 1535

Planetary
nebula

04h 14.3m

-12° 44.4'

Eridanus

10.5

60"

 

Planetary nebula NGC 1535 is a victim of circumstance. Take a look at its facts. Its bluish disk spans about a minute of arc, which is quite large as planetaries go, and shines brightly enough to be visible through giant binoculars. Its central star glows at magnitude 11.6, creating a surreal scene resembling a disembodied human eye, which led to the nickname "Cleopatra's Eye." Those in the know rate NGC 1535 as one of the sky's finest planetary nebulae. Yet this enticing target remains unknown to many backyard stargazers.

 

Above: Evening star map. Credit: Map adapted from Star Watch by Phil Harrington

Above: Finder chart for this month's Cosmic Challenge.
Click on the chart to open a printable PDF version.

 

 

NGC 1535's anonymity is due in large part to its empty surroundings within the vague constellation Eridanus the River. Eridanus, one of the sky's longest constellations, flows from the western edge of Orion southward below most of our horizons. Only if you are south of approximately 30° north latitude, you be able to see the River's lone bright star, Achernar [Alpha (α) Eridani], at the mouth. For the rest of us, Eridanus is a meandering group of faint stars in the otherwise empty abyss directly west of mighty Orion.

I suspect that most amateurs, at least those who prefer to starhop, feel that taking the extra time to zero in on NGC 1535 is just too much effort. The closest bright star, Rigel (Beta [β] Orionis), lies a distant 20° to the east-northeast. None of the nearby stars shine brighter than 4th magnitude. This makes NGC 1535 a challenge to find, but not impossible.

For you starhopping purists, scan about 1½° to Rigel's west-southwest to a short arc of three stars aligned east-west. The arc's brightest star shines at 4th magnitude and is labeled Lambda (λ) Eridani. Continue westward past the arc for 6°, or about a finderscope field, to the stars 55 and 56 Eridani, and another half-field further west to reddish 47 Eridani. Are we there yet? No, but we're getting close. Keep moving westward for another finder field to Omicron2 (ο2) Eridani and stop. From Omicron2, shift 2½° due south to 5th-magnitude 39 Eridani, then finally, another 2½° to NGC 1535. *phew*

If it's in your telescope's field of view, NGC 1535 should be immediately obvious -- no hunting required. Even at only 38x, my 4-inch refractor easily displays the planetary's pale steel-blue disk nestled in a sparsely populated field, as shown in the sketch below. Compare its appearance to that of Uranus or Neptune, and apart from the disparity in color, it's easy to see why early observers mistook these vaporous disks for distant, undiscovered planets.

 

Above:  NGC 1535 as seen through the author's 4-inch (102mm) refractor.

 

William Herschel was first to bump into NGC 1535 on February 1, 1785.  Modern views shown that NGC 1535 is very similar structurally to NGC 2392, the Eskimo Nebula in Gemini. Like the oft-observed Eskimo, NGC 1535 exhibits a brighter central core surrounded by a fainter outer halo.  The inner core comes alive in the image below taken by Adam Block. 

 

Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona
[CC BY-SA 3.0 us (https://creativecommons.org/licenses/by-sa/3.0/us/deed.en)]

 

Many people mistakenly think they are seeing the central star at low magnification, when in fact, they are seeing the nebula's bright inner core. To see the progenitor star itself, we need more power! Thankfully, NGC 1535 takes magnification well. My experience is that it takes 200x or more to isolate the star from the bright annulus that immediately surrounds it. In his book Hidden Treasures, author Stephen O'Meara notes his success through a 4-inch refractor operating at 504x, an incredible magnification for any telescope, but especially that aperture. My local seeing conditions never let me get anywhere near those crazy high numbers, but I have had success seeing the central star through my own 4-inch at 248x. To increase the odds of seeing the star, try looking with direct vision to better suppress the nebula's glow.

 

Speaking of hidden treasures, if you're viewing through a BIG scope, then after you drink in the beauty of NGC 1535, shift your attention 28' to its south-southeast to a slender diamond of four 10th- and 11th-magnitude stars.  Near the eastern facet of the diamond is the distant galaxy NGC 1538.  Lying 463 million light years away and shining at only 15th magnitude, NGC 1538 is classified as an S0 lenticular galaxy. Lenticular galaxies display large-scale disks, but do not have large-scale spiral arms.  For this reason, many were initially classified as elliptical galaxies until more detailed studies revealed their unique nature.

 

Good luck with this month's Cosmic Challenge! And be sure to post your results of both NGC 1535 (and NGC 1538) in this column's discussion forum.

 

Until next month, remember that half of the fun is the thrill of the chase.  Game on!



About the Author:

Phil Harrington writes the monthly Binocular Universe column in Astronomy magazine and is the author of 9 books on astronomy.  Visit www.philharrington.net to learn more.

 

A revised, second printing of Cosmic Challenge: The Ultimate Observing List for Amateurs is now available with updated data tables and charts for finding various solar system objects, such as Pluto and Vesta, as well as improved renditions of the many eyepiece sketches that accompany each of the 187 challenges encompassing more than 500 individual objects.  The book is available from Amazon.com.  

Phil Harrington's Cosmic Challenge is copyright 2020 by Philip S. Harrington.  All rights reserved.  No reproduction, in whole or in part, beyond single copies for use by an individual, is permitted without written permission of the copyright holder.

 


  • okiestarman56, John O'Hara, BoldAxis1967 and 1 other like this


3 Comments

Phil:

 

Thank you for another cosmic challenge. NGC 1535 is a favorite of mine, particularly in a large scope. As you say, its one of the most beautiful planetaries..

 

I locate it by starting at Zaurak, gamma Eradini (mag 3) and moving 4 degrees (one Telrad diameter) towards Rigel. NGC1535 is almost on a direct line from Zaurak and Rigel.

 

I do not believe I've seen NGC1538 so If it ever clears up, I have to give it a try.

 

Happy New Years

 

Jon

    • PhilH and Knasal like this
Thanks, Jon. Happy New Year to you, too.

Great target Phil.  Definitely missed its presence in the past, so I appreciate your exposing its presence.  jd

    • Jon Isaacs and PhilH like this


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