Dark Sky Hunting with Google Earth
Wow! Ok, so you’re already aware how cool Google Earth is. Zoom in on your postcode, see your house from above, peer into neighbours’ windows using streetview… But did you know you can overlay images onto the Google Earth globe?
With this tool, and given a map of light pollution for a certain area, you can overlay a light pollution map onto your globe and zoom in to find which areas around the world have darker sites.
Google Earth with Light Pollution
Here’s how:
1. Download Google Earth http://earth.google.co.uk/ and install it on your computer
2. Download the appropriate light polution map:
Artificial Sky Brightness (Western Europe): http://www.lightpollution.it/download/eurv1.zip or
Naked Eye Star Visibility (Western Europe): http://www.lightpollution.it/download/OUTLIM_01_V2bordi%20TIF.zip
3. Unzip the file (both of the above links are zipped files of large .tiff images) to a suitable location
4. Open Google Earth, click on Add > Image Overlay
5. In the “Image Overlay” box enter a suitable title, such as “Naked Eye Star Visibility”, then browse to find the .tiff file you saved in step 3.
6. Move the transparency slider to between 25% and 50%
7. Click on the “Location” tab and enter these co-ordinates:
Artificial Sky Brightness map
N: 71° 8’30.67″N
S: 34°51’31.13″N
E: 12°50’37.53″E
W: 10°26’29.69″W
Naked Eye Star Visibility map
N: 71°58’30.00″N
S: 31°59’27.92″N
E: 29°33’41.78″E
W: 10°32’14.46″W
This will overlay your Light Pollution maps onto the globe accurately (but you might want to tweak and fine tune to get the perfect fit – let me know if you get an even better fit than I did and I’ll adjust the co-ordinates above to match).
8. Click “OK” to finish. Now in your “Places” bar on the LHS you’ll see your overlays, with checkable boxes to enable / disable them.
Hints: I find it aesthetically more pleasing to disable Google Maps “Borders and Labels” in the “Layers” box
Happy Dark Sky Hunting!
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Great tool!
Just wondering whether you can make a high-res/high-sensitivity version for currently underpolluted light areas? if data exists?
I’m asking because my home is near Ullapool in the Western highlands of Scotland. Street lights are popping up like mushrooms in tiny villages, and it would be really useful to see the extent of the problem. The highlands are loosing their dark skies. Unfortunately this map doesn’t even show Ullapool (well, you have to look very closely), which is a fairly substantial town.
By the way – Ullapool (or another small town like it) might be a good way to do your coordinates, you might be slightly off (or my coordinate entering is slightly off) – see the splodge next to 57°53’51.07″N 5° 9’52.57″W (sorry I don’t have time to fix it myself right now)
cheers,
Vivienne
Hi Vivienne,
Glad you enjoyed the Google Earth LP overlay.
Actually, I’m a highland lad myself; born and raised in Inverness, so I know Ullapool well. Shame your dark skies are being encroached upon by more and more lighting…
The light pollution map files you overlayed are the highest res we have I’m afraid, but that’s not to say that you couldn’t get a more accurate map, you’d just have to make it yourself!
It’s fairly easily done, assuming you have the time and the inclination.
For a very accurate map you’ll need to buy a Sky Quality Metre, manufactured by a company called Unihedron: http://www.unihedron.com/projects/sqm-l/
You’ll want to get the SQM-L, which is their hand-held device, and costs about $135. You can also get ethernet (SQM-LE) and USB (SQM-LU) ones for continuous readings.
These devices give you a reading in magnitudes per square arcsecond (basically brightness per unit area in the sky). In a city you’d read about 16 mags/sq arcsec. In the deep highlands you’d read about 22 mags/sq arcsec.
You could make monthly measurements in key parts of Ullapool and record them on Google maps, which would allow you to quantify the increasing brightness of your night sky.
Oh, and if you’re serious about tackling light pollution in your area you should look at the Campaign for Dark Skies website for advice on approaching businesses / council etc http://www.britastro.org/dark-skies
Happy Stargazing
I’ve used the light pollution overlay for Google Earth (I
have two versions) a few times but I was never really pleased with
the alignment. I found that for some cities the alignment was off
by as much as 10 km; pretty confusing in some cases… After some
fine-tunning I got to some new coordinates for the Naked Eye Star
Visibility map: N: 71°59’48.40″N S: 31°59’56.81″N E: 29°29’37.29″E
V: 10°30’16.66″W To me it seems that the alignment is almost
perfect with this values. By “almost perfect” I mean the high
pollution areas match the exact position of as much of the large
cities as possible. Hope you’ll find this useful. Clear
skies!