How Low Can You Go? Journey to the Backside of the Sky

June 26, 2019 - Comment

We regularly ignore celestial objects that solely peep over our southern horizon as a result of they’re compromised by thick air and haze. Let’s plow by anyway and uncover simply how a lot you CAN see.  Star clusters M7 and M6 in Scorpius by no means get far above my native horizon — eight° and

We regularly ignore celestial objects that solely peep over our southern horizon as a result of they’re compromised by thick air and haze. Let’s plow by anyway and uncover simply how a lot you CAN see. 

Star clusters M7 and M6 in Scorpius by no means get far above my native horizon — eight° and 11° respectively — however  they’re fantastic sights all the identical.
Bob King

Relating to deep sky, I am going to do virtually something. Stand on a teetering ladder, journey 100 miles to darkish skies, arrange the scope on the fringe of a mosquito-infested bathroom, or sit within the dust to glimpse an impossibly low planetary nebula. One time I attempted to (and succeeded in) observing NGC 3132, the brilliant “Eight-Burst” planetary nebula in Vela. At declination –40° 26′, it stood simply 2.5° above my southern horizon. Atmospheric extinction at that altitude dimmed it practically 4 magnitudes, from 10 to 14. Certain, it was faint, however I may clearly make out its form in my 11-inch scope.

Are you a bottom-feeder, too? Among the greatest deep-sky objects lurk within the bellies of constellations that scud throughout the southern sky. Naturally, we wish to observe any object when it is excessive within the sky and least obscured, however for objects with southerly declinations, that luxurious requires journey. Beneath the precise circumstances — haze-free skies and good seeing — you’ll be able to see virtually something your latitude permits.

Seeing through soup

The farther you look from the zenith (a.ok.a. zenith angle) the extra the ambiance dims a star, a phenomenon known as atmospheric extinction. The quantity of air straight overhead is known as one air mass. For a star 30° above the horizon, you are trying by two air plenty. At 10°, 5.6 air plenty, and for an object on the horizon, 40 air plenty. A star overhead is dimmed zero.16 magnitude, whereas one 10° above the horizon seems zero.90 magnitude fainter. At 5° altitude celestial objects are dimmed by three magnitudes.
Courtesy of Mike Luciuk and Beginner Astronomers, Inc.

I all the time test an object’s coordinates earlier than making a name on whether or not it is seen from my 47° north latitude location. Objects with a declination equal to your latitude will move by the zenith. For me that is +47°. Objects on the celestial equator have a declination of zero° and attain peak altitude when due south on the meridian. My equator stands 43° excessive on the meridian.

Forty-three levels under the equator I hit the horizon at declination –43°. Clearly, I am unable to see something that far south, but when it is three°–four° north of that, and I view it close to the time of meridian passage, it is price a attempt.

Digging right down to southern declinations feels a bit like doing the limbo. My limbo declination zone spans from about –33° to –40°, the place a deep sky object peaks between 10° and three° altitude. You may decide the declination of your native horizon by subtracting your latitude from 90°. If you happen to reside at 30° N, your horizon reaches right down to declination –60° (90° minus 30°). If you happen to’ reside at 42° N latitude, it bottoms out at –48°.

Making a Limbo Checklist

Cosmic bow tie

Certainly one of my favourite horizon-scrapers is the Bug Nebula (NGC 6302) at –37° declination. Additionally known as the Butterfly, it is a planetary nebula. What appear like dainty butterfly wings are literally roiling cauldrons of gasoline heated to greater than 20,000°C by a super-hot white dwarf star hidden by an equatorial band of darkish mud. The gasoline is tearing throughout area at greater than 965,000 km an hour.
NASA / ESA / Hubble SM4 ERO Workforce

As soon as you have decided the bottom declination seen out of your location, you will subsequent must discover a strategy to plumb it. I maintain a number of observing websites, together with one the place I can dig right down to my southern restrict. It is not more than a notch within the tree line however it’s my window to wonders if I time issues proper!

In case you have entry to a big subject or lake, you’ll be able to most likely see inside a couple of levels of your restrict, like I can. If that is not attainable, discover a gap between bushes, mountain peaks, or buildings and stalk it till the appointed meridian passage. Due to extinction (and relying on the dimensions of your binoculars or telescope), choose the brightest deep-sky objects and take a look.

As a result of we do not essentially share the identical latitude, your limbo checklist will differ from mine. That maxim contains Southern Hemisphere observers hoping to catch sight of northern deep-sky objects just like the Andromeda Galaxy or the M81 / M82 galaxy pair.

Goin' low

This map highlights 11 pleasant objects with southerly declinations seen from the northern U.S., southern Canada, central Europe, and factors south. Declinations are labeled at left and stars are proven to magnitude eight. The NGC prefixes are omitted to keep away from litter. The map is drawn for 11 p.m. native time in late June, going through south. Objects on the map that I could not see however could also be seen to you’re lettered in grey. Click on to enlarge.
Stellarium with additions by the writer

For skywatchers within the Northern Hemisphere, summer season is an auspicious time of 12 months for low-hanging goodies due to the arrival of Scorpius and Sagittarius, each soaked in Milky Means splendor. I’ve ready an inventory of deep-sky objects and double stars seen from northern Minnesota to assist get you began. Most of the targets are magnitude 9.5 or brighter. If you happen to personal a refractor or SCT, you may want a step stool to succeed in these, however Dob homeowners will undoubtedly discover it extra comfy to simply sit on the bottom. I do not thoughts being “grounded” whereas observing cosmic objects. I just like the distinction between the gritty Earth and people far-away, cosmic visions pouring by the eyepiece.

Journey to the Backside of the Sky

We’ll begin in Lupus, the Wolf, and head east to Scorpius. My observations had been made with a 15-inch reflector underneath Bortle three (rural) skies:

Packs 'em in

Situated 104,000 light-years from Earth, NGC 5824 is a extremely compressed globular.
NASA / ESA / Hubble

Globular cluster NGC 5824 (R.A.15h 4m, Dec. –33° 04′; Magnitude 9.1) — Simply noticed at 64× magnification. About 2′ in diameter with a brilliant, very compressed core like a faraway model of M15. At 142× the core seems dense and practically stellar with a large halo out to four′. Faint granulation seen inside the interior a part of the halo. Very satisfying view!
Planetary nebula NGC 5873 (R.A.15h12m, Dec. –38° 07′; magazine. 11) — Small, fuzzy “star” at 64× increasing to a 15″ misty ball with a brilliant, starlike heart. A UHC nebular filter enhanced its brightness relative to the background sky and made the core positively blaze.
Globular cluster NGC 5986 (R.A.15h46m, Dec. –37° 47′; magazine. eight ) — Reasonably giant (5′) cluster with a broadly brighter heart. Good decision of the outer halo at 142× and with averted imaginative and prescient. One standout brighter member punctuates the halo northwest of the core.
Double star Xi1,2 (ξ1,2) Lup (R.A.15h 56.9m, Dec. –38° 07′; mags. 5, 5.5; sep.10.four″ in P.A. 49°) — Vibrant, barely unequal pair actually jumps out even in poor, low-altitude seeing. Though they’re classed as A and B stars respectively, my eye noticed pale yellow.
Double star Eta (η) Lup (R.A.16h12.1m, Dec. –38° 23.6′, mags. three.four, 7.eight; sep. 20″ in P.A. 20°) — Fantastic distinction to Xi. Vibrant main with a tiny Eighth-magnitude companion. Jogged my memory of Rigel.

NGC 6026 is a sexy planetary in Lupus. It was initially categorised as an elliptical galaxy however confirmed in any other case with a spectrogram in 1953.
DSS2 / Aladin Lite

Planetary nebula NGC 6026 (R.A.16h01m, Dec. –34° 32′; magazine. 12.9 ) — A faint, arcminute-wide diffuse glow by the O III filter. Simple to identify at 64× and 142×. Vibrant, 13th-magnitude central star seen in any respect powers.
Planetary nebula NGC 6072 (R.A.16h13m, Dec. –36° 13.eight′; magazine. 14 ) — Almost unimaginable to see with no filter. A lot improved with the O III! I discerned a 60″ disk with mottling and hints of annularity. No central star seen.
Globular cluster NGC 6139 (R.A.16h27.7m, Dec. –38° 50.three′; magazine. 9.7 ) — Barely seen whereas sweeping the place at 64×. Upping to 142× revealed a tiny cluster simply 1.6′ throughout with a brilliant core.
Open cluster NGC 6242 (16h55.6m, Dec. –39° 28′; magazine. 6.four ) — Situated simply 1.5° south-southeast of Mu (μ) Sco. Vibrant, 9′ extensive, north-south elongated patch of stars. Though it stands out effectively, the cluster’s on the sparse aspect with 23 members. Low energy is greatest.

Within the 19th century, James Dunlop described the cluster as a “curiously curved line of fairly brilliant stars, with many stars mixt.” What’s going to you see?
Digital Sky Survey 2 / Aladin Lite

Open cluster NGC 6281 (R.A.17h04.7m, Dec. –37° 59′; magazine. 5.four ) — Very fairly group elongated north–south and about eight′ throughout. Good mixture of brilliant and faint stars with 70 members complete. From the southern U.S. this cluster is seen with the bare eye. Beautiful at low magnification.
Bug lookalike

Sketch of NGC 6302, which vaguely resembles the planet Saturn in define.
Bob King

Planetary nebula NGC 6302 (R.A.17h13.7m, Dec. –37° 06′; magazine. 9.6 ) —The Bug Nebula was apparent even with no nebular filter. The nebula was elongated east–west with a brilliant, dense, non-stellar central area flanked by extensions on both aspect, shorter and fainter to the east. I spied a faint knot (star?) within the west wing. Finest views had been at 142× with the UHC filter.

If the map above would not suit your wants, I’ve additionally created variations for 40°N and 30°N latitude — simply click on the hyperlinks to get ’em. Or create your individual custom-made map utilizing free plotting software program like Cartes du Ciel or Stellarium. Set your latitude, activate the deep-sky object catalogs, and also you’re able to go. Completely satisfied trails in your southbound (or northbound) journey!

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