Bortle Dark Sky Scale: The Bortle Dark Sky Scale was developed by John Bortle “based on nearly 50 years of observing experience,” to describe the amount of light pollution in a night sky. It was first published in a 2001 Sky & Telescope article.

Depending on the device you are using, it may be necessary to slide the chart to the right to see in its entirety.

Number Code

Map Color Code

Label

Sky Mag.

Naked Eye Limit Mag.

320mm Limit Mag.

M33 visible?

M31 visible?

Central Galaxy visible?

Zodiacal light visible?

Light Pollution

Clouds

Ground Objects

1

excellent dark sky

22.00–21.99

≥ 7.5

> 17

obvious

.

casts shadows

striking

airglow apparent

.

visible only as silhouettes

2

average dark sky

21.99–21.89

7.0–7.49

16.5

easy with direct vision

.

appears highly structured

bright, faint yellow color

airglow faint

dark everywhere

large near objects vague

3

rural sky

21.89–21.69

6.5–6.99

16.0

easy with averted vision

.

complex structure

obvious

LP on horizon

dark overhead

large distant objects vague

4

rural/suburban transition

21.69–20.49

6.0–6.49

15.5

difficult with averted vision

obvious

only large structures

halfway to zenith

low LP

lit in distance

distant large objects distinct

5

suburban

20.49–19.50

5.5–5.99

14.5–15.0

.

easy with direct vision

washed out

faint

encircling LP

brighter than sky

6

bright suburban

19.50–18.94

5.0–5.49

14.0–14.5

.

easy with averted vision

visible only near zenith

.

LP to 35°

fairly bright

small close objects distinct

7

suburban/urban transition

18.94–18.38

4.5–4.99

14.0

.

difficult with averted vision

invisible

.

LP to zenith

brilliantly lit

.

8

city sky

< 18.38

4.0–4.49

13

.

.

.

.

bright to 35°

.

headlines legible

9

inner city sky

.

≤ 4.0

.

.

.

.

bright at zenith

.

.

My view to the east (last night @ 9:15 PM, November 18, 2023 from my back deck) showing the light pollution at about 15º above the treetops.

I always try to observe deep-sky objects at least one hour or two from the meridian.

It is difficult to see the Pleiades “visually” at this low altitude. I was using an iPhone 14 “handheld” to make a photo for illustrative purposes.

The Pleiades was my first deep-sky object when I was 12 years old. I remember so well, walking out in my front yard in about mid-November and seeing this cluster rising above the treetops.

At that time, I had no clue as to what this group of stars were.

A year or so later I found out it was the Pleiades, M45 and my interest in amateur astronomy began, which continues to this day. Interesting to note: This was Leslie Peltier’s first deep-sky object also, as probably so many others.

The following photo:

Andromeda is difficult for me visually, and requires averted vision. At the meridian, it can be fairly easy, but averted vision still works best.

The following photo using my phone, presents the galaxy quite a bit brighter than naked-eye.

So, I estimate the Bortle Scale from my backyard to be ~6.5. I think we can all agree, the Bortle scale is not a definitive number, but using this criteria can describe an observing site pretty accurately. I’d say John Bortle developed an excellent, simple and objective measurement system for judging different observing sites, and for comparison with others.

Meade introduced their Deep-Space telescopes in about the early 1980’s which caught my eye in magazine advertisements.

I was looking for something larger than my 4.5-inch reflector which I was using at that time. The Deep-Space series consisted of two telescopes: A 10-inch and 16-inch f/4.5 telescopes with equatorial mounts.

This was at a time when Meade was building their serious Newtonian’s in their Costa Mesa, facility, which included grinding and polishing mirrors. All of the hardware, bolts and Allen heads on these telescopes and mounts are SAE (Society of Automotive Engineers) and not metric.

Meade, at about this time had just built a state of the art facility in Irvine, California. They were building their Schmidt-Cassegrain telescopes (complete) including the mirrors, coring and the mounts. And at this time they began to make their full line of high-quality refractors with ED glass. This included their German EQ style GoTo mounts, and also the Meade ETX Astro 90mm Maksutov-Newtonian telescopes.

The ETX 90 was a novel idea: To build an incredibly low priced high-performance telescope with all the money and effort going into the optics. The base and arms were made of plastic, but the optical tube was beautiful anodized aluminum.

The ETX 90’s (the ones built in California) indeed had excellent optics. I purchased one shortly after they were introduced, and can attest to the quality of the optics. The later ones that were built in China and Mexico might have been equally as good, but never had the opportunity to test one.

Meade would later send all manufacturing to China and Mexico. Meade, began having quality issues and customer service became nonexistent. However, as a disclaimer (this information is from hearsay) or from online, or other articles. This might be considered the beginning of the end for a former great American company that was started in 1972 on a kitchen table. Orion Telescopes and Binoculars, would later purchase Meade, but would declare banruptcy a few years later.

The following is a Meade advertisement from almost 40 years ago as of 2024:

My local astronomy club (at that time) had a DS-16 which was a two-person job to set up.  I could take the 16-inch and use at any time. However, this thing was a monster, and where would I store this behemoth of a telescope? I didn’t and still don’t have a permanent observatory, and how would I set it up by myself? The 16-inch was definitely not for me!  The 10-inch seemed to be the perfect larger aperture telescope and with an equatorial mount. I had always liked the simplicity of a Newtonian, and an equatorial mount was a must.

Astronomy Magazine test and evaluation:

Astronomy Magazine tested a 10-inch DS-10A (The 10A was an updated version with a 2-inch focuser, setting circles and RA drive) with Astronomy Magazine giving the test mirror a rating of a B+.  

So, in February 1992, I purchased the 10-inch from Pauli’s Wholesale Optics, in Danbury Connecticut. It was Fred (the owner of Pauli’s) that recommended this telescope.

And now with over ~2,000 hours under the night sky and over 1,500 deep-sky pencil sketches and even more observing notes. I made the right decision and 33 years later as of 2025, I continue to use and enjoy this telescope, which is still in pristine condition. (See the photo below)

I have spent over ~2,000 hours at the eyepiece as of 2025. This would be the equivalent to 50 weeks working a job at 40 hours per week, which makes for a good prospective or comparison.

My other telescopes include a 102 mm refractor, 6-inch f/6 reflector, 80 mm f/5 refractor, Celestron 76 mm reflector First Scope (anniversary edition) and a couple others.

Shown below is the original mount, which I use when observing deep-sky objects that can’t be observed from my back deck. Only objects greater than +05º north declination (my house gets in the way) and allows me to use the Celestron CGE-Pro mount. It’s just not portable enough to use beyond my deck. Southern objects require that I use the original Meade mount, which I consider very portable.

The original medium-duty EQ mount:

For efficiency, I use both the RA and Declination circles to get me within ~1/2º degree of my target. At this point, I use a star atlas to zero in on my deep-sky object. Note the 6-inch Parks Optical declination circle and a fabricated index pointer.

The low pedestal mount is perfect for use with an astro-chair, when making observing notes and pencil sketches at the eyepiece. As for me, it’s impossible to observe and sketch while standing.

The original mount as pictured below is a medium duty mount, but is remarkably sturdy, due in-part to the very short pedestal. After spending so many years star-hopping to locate deep-sky objects, my favorite mount to use is the Celestron Pro mount, which I’ve had for only eight or so years. Again, can only be used for objects +05º north declination and greater, due to my house.

Both mounts, side by side for a comparison:

The Celestron mount is too large and heavy to take in and out of the house, so this Rubbermaid shed on my deck works well for storage. I also cover (inside the shed) the mount with a soft blanket and a piece of auto-marine fabric for extra protection.

The original mount is fairly easy to carry in-and-out, and can be stored in the corner of an extra bedroom.

A sample of a few of my sketches, using only a pencil, and a 5 x 8 blank notecard. My “humble sketches” are all raw sketches, as they appear to me through the eyepiece, without any computer enhancements. I try to make my sketches as accurate as possible, with any embellishing.

IC 5146 “The Cocoon Nebula” In Cygnus

NGC 2024 Nebula in Orion

M42: Orion Nebula Complex

M106 Galaxy in Canes Venatici

NGC 3079 Galaxy in Ursa Major

Messier 20 In Sagittarius

Messier 85 and NGC 4394

Comet Hale-Bopp: Charcoal pencil on black card stock, showing all three-tales; the gas tail, dust and anti-tail. April 1997

Messier 81 with spiral arms

NGC 7479 Galaxy in Pegasus

The Rosette Nebula

NGC 5689 Galaxy in Bootes

Messier 33

My wife (on occasion) uses the 10-inch to take photos of the moon:

I continue to ride, but “absolutely certain” I’ll not be able to ride another 100,000 miles. My rides in recent years are quite a bit shorter and much slower, but more fun.

Date: October 9th 2023:

I’ve went from an 80mm f/5 refractor to this 10-inch Newtonian in just a matter of days. So, I’m proud of the progress I’ve make, from never using a camera with a telescope, to “at least” an image of the moon. And all within a week!

I changed some settings on my camera, something I’d never done before. It had been set on ISO 100, for my everyday snapshots, and changed to ISO 400 this morning for this moon shot. I was amazed how much brighter the moon was when focusing through the camera using this 10-inch versus the 80mm refractor.

For sure a lot easier to focus with the brighter view due to the size of the telescope.

The field using this telescope is really narrow and small as this photo shows. Now I’ve got to figure out how to set the “exposure time” for some small and bright deep-sky objects.

I’m actually amazed that I could do this...and hopefully more and better to come. Debbie

Telescope: 80mm: 400mm Focal Length: f/5

Camera: Nikon D3300

Nikon T-Adaptor

Camera Setting: Manual

Vixen GP Equatorial Mount

The following photo was made after sunrise

Nikon T-Adaptor

I also made a photo as following using a 10-inch f/4.5 EQ telescope. Roger had using this telescope during an early morning 4:00 AM observing session of a galaxy. So, before bringing it back into the house, he suggested I try a moon photo with this telescope. This is my photo.

The following solar project was suggested by Tom English:

Place a straight pole into the ground, facing due south, and at an angle of 55 degrees:

Then on the two equinoxes (the first day of spring, and the first day of fall) the sun will cast no shadow, as the sun will be shining directly down the steel rod.

Note: Tom was formerly an astronomy and physics professor at Gardner-Webb University for many years, but now teaches in Greensboro. However, we still stay in touch.

During more than a decade, we spent many nights in my backyard with telescopes, enjoying observing galaxies, nebulae and star clusters. Tom would often bring an 8-inch Celestron Orange-Tube SC telescope, and we’d compare views with my 10-inch Newtonian.

The Celestron Story: https://rogerivester.com/2022/09/26/the-8-inch-orange-tube-schmidt-cassegrain-f-10-telescope-founder-tom-johnson-and-other/ 

So, on June 21st, 2023 (Summer Solstice) the shadow will cast its greatest extent southward, and on the Winter Solstice (December 22nd 2023) the shadow will cast its greatest extent northward on the stick.

My latitude in North Carolina: The Latitude is 35º 15 mins

So a simple calculation to determine the angle of the rod.

(90º – 35º) = 55º

Debbie using an angle finder to determine 55º.

The angle of the rod is toward the South at 55º. So draw a line, with the post, going South to North.

Note the shadow: It will be increasing, each day, and getting shorter, until September 23rd, when there will be no shadow, as the sun will be “pointing directly down” the rod.

At 1:00 PM EDT, today (September 22nd) a photo was made, and indeed showing no shadow, as the sun was shining directly down the steel rod. September 22nd or 23rd…close enough.

The following photo:

The yellow mark indicated the sun shadow on August 24th, and the position of the sun shadows on different days following.

The red mark was made on October 4th.

The black mark was made on October 13th 2023. Note the rapid movement of the sun heading south in less than two weeks!

Note: The crossbar on the rod is for pushing in the ground with my foot, and nothing more.

Cocoon Nebula in Cygnus: Very faint and difficult, but with patience and a “reasonably” dark-sky it’s possible. Look for the tiny star chain, just to the NE and you know, you’re close to the Cocoon.

Comet Hale-Bopp With All Three Tails Being Sketched: The Gas Tail, The Dust Tail and The Anti-Tail. Chalk sketch on black card stock. (March 1997)

10-inch EQ f/4.5 Newtonian Telescope: Nine Galaxies in a 1/2º Field-of-View, around M84 and M86

I’ve been having to reset the time or clock on my Celestron CGE-Pro equatorial mount before observing. I just recently found out from others, there is a CR2025 battery that requires changing from time to time.

Celestron calls for a CR2025 as a replacement battery.

Re: Replacing the internal battery in a Celestron CGE-Pro Equartorial Mount from Celestron online, as following:

The battery is located under a clip on the PC > Autoguide > Power Cord board inside the pier. Replace with a 3-volt CR2025, available at many drug, photo, and hardware stores.

It’s actually a fairly straight forward process, but “can be” time consuming.

There are a lot of electronics surrounding this battery…so you don’t want to damage your mount electronics due to an inexpensive leaking battery.

The bolts that hold this top cap are Allen heads requiring a 5.5 mm wrench. Seldom do I find any application, involving telescopes, high-end precision bicycles or other that require half sizes, but this is no problem.

The following plate was a bit difficult to remove. It was “stuck” and required attempting with several techniques before finally getting it out. It had drops of silicon in several places along the edge, which had to be removed and cleared before removing the aluminum plate.

I found that using Allen wrenches “to hook under the two larger holes” in conjunction, and then pulling up was successful.

Use care as not to damage the plate, or some of the ribbon wires, located just underneath the plate.

When installing the new battery, I used “nitrile powder-free gloves” to avoid getting finger oil or grease on the battery.

Remove the old battery, insert the new one, and then reassemble the mount, connect the Dec and RA cables and you’re all finished.

However, everything related to time and dates will have to be changed via the hand controller.

Storage:

I had set the clock, and checked all other specifications during this afternoon. However, last night when performing the alignment process, the mount couldn’t even find Vega, just overhead. And could not perform any two or three star alignment.

So finally, after at least an hour of frustration…I did a “complete factory reset” and reentered all necessary information which resolved the problem.

Note: After the battery change, the time is perfect, each and every time.