Omega Nebula, M17

NGC 6618 in the Constellation of Sagittarius

Image exposure: 120 minutes

Image field of view: 91.1 x 59.7 arcminutes

Image date: 2021-08-12

The suburban night sky was clear and beautiful but I was the only person around to witness the dazzlingly brilliant Venus sinking down to the Western horizon, closely pursued by a growing crescent Moon. No people outside. No cars. No dogs barking. No noise at all. Another lock-down night and what was to be my last observing night before moving my telescope from my favourite viewing spot in the front garden into the seclusion of the back garden. Just me, the sky and and that pesky street light* (See below).

My target for the evening was Messier 17, crossing the meridian, high in the sky. The nebula is located in a rich Milky Way star field.

M17 is a bright red HII emission nebula, taken with a narrowband Ha and [OIII] filter to accentuate the contrast. All light is blocked by the filter, apart from the hydrogen and oxygen emissions of the glowing gas, caused by the high intensity ultra-violet light pouring away from the new born stars recently formed within.

Inside the nebula are about thirty-five young stars, 20-30 times brighter than the Sun but not visible at optical wavelengths. They will ultimately emerge as an open star cluster after the intense UV light erodes the gaseous nebula.

As with many astronomical objects, the Omega Nebula is listed by different sources as being at various distances. In this case, between 4,200 and 6,000 light years. It spans around 40 light years.

We do know that its brightness is magnitude +6.0 and its apparent diameter is 46′ x 37′.

My understanding is that the name Omega came about because of its distorted resemblance to the Greek letter Ω. It is also known by several other names, including: Checkmark Nebula, Horseshoe Nebula, Lobster Nebula, and the Swan Nebula.

_{Sagittarius
Image Source: Wikimedia Commons}

nova.astrometry.net

Warning: Soapbox alert!!

That e @#$%^&!! Street Light

I’ve mentioned the street light quite a number of times in my blogs, most notably > here < and > here <.

My New Enemy, the new street light, unnecessarily bright on an unnecessarily taller pole. It should have been designed to just illuminate the street but – being without any shrouding – also illuminates all the properties in the street as well. 50mm fixed lens, f/2.2, ISO 100, 1.3 second exposure. (2019-11-14).

To summarise, in 2019 they raised the height of the column, so it spread the light more widely and they replaced the metal-halide lantern with a much brighter LED fitting with no glare control, also spreading more widely. Not downwards but sideways. ☹

I had no astronomical grounds to complain about the shockingly bright glare from the light. After all, if I set up my telescope near the street, then I should expect street lighting interference. However, the light shone at almost eye-level as either my Bride or I stepped outside the front door. It also shone horizontally into my neighbours windows and would have shone into ours too if we didn’t have roller shutters.

I had already built myself a portable glare control screen to protect my telescope from the bright light, so my application to Council was only concerned with the blinding glare at the front door.

Many months and several e-mails later, the light was finally modified and the glare was considerably reduced (but not eliminated), making it somewhat safer for us to walk out the front door. 😄

It took them less than five minutes to do it, just a few days ago – just after I had relocated the telescope to the back!

Good Street Lighting Design

Here’s a simplistic guide to Good Street Lighting Design Practice. Only the last of the four options below complies with Australian Standards. It saves wasted light, it saves energy, it saves $$$$$, it stops glare, it’s less intrusive, it lessens confusion for bird-life and is safer for humans. Lastly, it helps preserve the night sky.

If I were an Electrical Design Engineer

Actually I am an electrical design engineer.

I would not have lasted very long if I took on the job of street lighting design for local councils.

After all, I would have wanted to design every job properly. I would not have wanted to specify cheap lighting fixtures which contravene the Australian Standards and irritated the ratepayers with excessive glare and light spillage on their property.

Which is what happens everywhere around here.

Rant over.

Thanks for reading!

Cosmic Focus Observatory

Above us only sky….

Telescope:	SkyWatcher Esprit 120 mm apochromatic 3-element refractor; 840 mm f/l @ f/7.
Optics:	Field flattener; ZWO duo narrowband Ha + [OIII] filter.
Mount & Guiding:	SkyWatcher EQ6-R Pro mount.
Imaging camera:	ZWO ASI 071 MC cooled.

Images © Roger Powell
Cosmic Focus Observatory, 34° S
I’m a founder member of Macarthur Astronomical Society and current webmaster.

🙃