OBSERVER’S CHALLENGE* – November, 2022
by Glenn Chaple
NGC 7184 Barred Spiral Galaxy in Aquarius (Magnitude 10.9; Size 6.0’ X 1.5”)
Visual astronomers are always advised to observe a sky object when it’s as high above the horizon as possible. This month’s Observer’s Challenge, the barred spiral galaxy NGC 7184, makes this piece of advice difficult to follow. Located in the constellation Aquarius at a declination of nearly -21 degrees, it’s never very high above the southern horizon for astronomers living in mid-northerly latitudes.
NGC 7184 is located at the 2000.0 coordinates RA 22h02m39.8s, Dec. -20o48’46”. It can be found by star-hopping from the stars gamma (γ) and delta (δ) Capricorni (the stars that form the tail of the Sea-Goat). An alternate and more direct route can be had with a westerly star-hop from the 5th magnitude star 41 Aquarii.
When William Herschel discovered this object on October 28, 1783, he described it as “Faint, considerably large, much extended, brighter in the middle, easily resolvable.” Faint it is – especially if you live in an area cursed by a light-polluted southern horizon!
My initial attempt at NGC 7184 with a 10-inch f/5 reflector drew a blank – a bigger scope would be needed! A few night later, I teamed up with fellow ATMoB member Steve Clougherty to use the club’s 25-inch f/3.5 Dobsonian-mounted reflector. I was able to aim the big scope at the desired location, but it was Steve’s trained eye that picked out NGC 7184. The 25-inch failed to reveal the outer spiral arms, capturing only a circular smudge that proved to be the galaxy’s core. Bright lights from a shopping center a few miles to our south proved to be our undoing.
Imagers or visual observers working with medium to large aperture scopes under dark sky conditions will make out the details Steve and I missed. Most notable is a bright inner ring formed by the spiral arms. Whether you capture this intricate detail or merely catch a fleeting glimpse of a hazy circular smudge, you’re looking at light that left this galaxy some 115 million years ago.
*The purpose of the Observer’s Challenge is to encourage the pursuit of visual observing. It is open to anyone who is interested. If you’d like to contribute notes, drawings, or photographs, we’d be happy to include them in our monthly summary. Submit your observing notes, sketches, and/or images to Roger Ivester (email@example.com). To find out more about the Observer’s Challenge, log on to rogerivester.com/category/observers-challenge-reports-complete.
NGC 7184 (magnitude: 10.9, size: 6.0’ X 1.5’)
2000.0 coordinates RA 22h02m39.8s, Dec. -20o48’46”
Wide-field chart. Bright stars in upper right are the “tail” stars in Capricornus. γ and δ Cap. Magnitude 5.1 and 5.3 stars at lower left are 41 and 47 Aquarii, just west of the Helix Nebula. North is up; limiting magnitude is 9.0.
NGC 7184 Finder Chart A
NGC 7184 Finder Chart C
Stars to magnitude 13.5. Bright star at lower right is the star near the bottom center of Chart B.
NGC 7184 Image
Mario Motta, MD. “Taken with my 32 inch F6.5, 1 hour Luminance, then 1 hour Blue, 30 min green, and 45 min red filters. I tried H alpha, but the signal was poor in that filter, did not include in processing. Taken with ZWO ASI6200 camera.”
NGC 7184 Sketch
Glenn Chaple (ATMoB)