Thursday, September 18, 2014

Star trails in Australia

One of the original testers* of the Loss of the Night app recently created this cool photo of star trails far from city lights in the Outback of Australia:

South Celestial Pole Star Trail by Andrew Cool is licensed
under a Creative Commons Attribution 4.0 International License.

Andrew says that there was a great amount of green airglow visible on the night he made the photos. The image was originally published by the Planetary Society.

*I was very grateful for Andrew's help in testing the app in the Southern Hemisphere. It turned out that the first version we gave him to test asked him to look for the stars that were currently up in the sky... over Germany! So Andrew was left staring at his boots instead of up into the sky.

Monday, September 15, 2014

Moon free observing period has started

The 9th period of GLOBE at Night's 2014 campaign begins tonight, and that means that Loss of the Night app observations are possible again as well. The current observation period lasts until September 24 (and several days later for our app, if you're willing to stay up until the moon sets).

Tuesday, September 9, 2014

Can you see colors and read text under (full) moonlight? Yes!

If you look around the web for the answer to this question, you'll find a lot of conflicting information. A number of seemingly authoritative sources declare flat out that colors cannot be seen under moonlight, because the eye's cone cells are not active. The same sites also often mention that normal sized printed text cannot be read in moonlight, because the central fovea is packed with cones that won't be active. Both of these claims are false.

Since this is something that's really easy to test, there's no reason for this misconception to persist. All you have to do is wait for a night with a full moon, find a place outside that doesn't have any direct lamp light (e.g. a park), take something colorful with you (e.g. a children's book), and see if you can recognize the colors or not.

I did it last night, with Mr. Forgetful:

I found out the answer right away: I was able to distinguish the red hat and blue body not as different shades, but as "red" and "blue". I did have more trouble on some other pages. For example, on the page below I was pretty sure that the "grass" wasn't green, but I had no idea what color it was. When I went back inside I found out it was not actually grass, but brown dirt:

I also had no trouble at all reading the text, which is probably about 14 point font. I tried reading a text with a smaller font, and while I had a bit more difficulty, it was certainly still possible.

But please don't take my word on this! This is a science experiment that can be performed by anyone without vision impairment, so the next time there's a full moon, go out and try it yourself!

You might ask why any of this matters. It turns out that this actually came up one time in court! A witness claimed to have seen a red car under moonlight, and experts called to testify disputed the fact that such a feat was even possible. The case motivated some Australian researchers to do a controlled test. It turns out that certain colors are easier than others (red is the easiest), and the color of larger objects is easier to discern than smaller objects.

But there's another reason why it's important. The confusion online demonstrates the extent to which vision at night is poorly understood. It's almost certainly the case that lighting levels in our cities could be dramatically reduced without meaningful effects on visual performance. Doing so would save money, energy, might help people sleep better, and would bring many stars back to our urban skies. But how low can we go and still be able to see well on city streets? The world spends something close to 100 billion dollars per year on outdoor area lighting, so spending a few million to get the answer could result in a massive payback in reduced electricity bills.

Monday, September 8, 2014

The harvest moon and lunar elevation

Tonight is the full moon, and since it's the moon closest to the autumnal equinox, it's the "Harvest Moon". I found a number of explanations of why it's called the harvest moon online (e.g. this one by Bob King), and everyone mentions the fact that for several days, the moon rises near the sunset time. The moon therefore allows people to bring in crops by moonlight, hence "harvest" moon. I'm not a historian, but I have a very strong suspicion that this is only a part of the story.
autumnal equinoxa
autumnal equinox
autumnal equinox
autumnal equinox
autumnal equinox

Moonrise over Nationalpark Müritz by Alejandro Sanchez de Miguel is licensed
under a Creative Commons Attribution 3.0 Unported License.

If you think back to a memory of walking through the country on an extremely bright moonlit night, the odds are very good that you'll be thinking of a snow-covered winter landscape. Snow of course makes the landscape much brighter, but full moons are also brighter in winter because the full moon rises much higher in winter than it does in summer. (A useful way to remember this is that the full moon always does the opposite of the sun: in summer it's low in the sky, and in the winter it's high).

But it's a bit more complicated in the spring and fall. At those times, the highest elevation moons are during either the first quarter (spring), or the third quarter (fall). Now here's where I think the "harvest" moon comes in. In the days shortly before the full moon in autumn, the moon sets shortly after midnight, and the landscape isn't particularly brightly illuminated because the moon doesn't rise very high in the sky (both of which are not so useful if you want to work all night). In contrast, the moon soars high in the sky in the days immediately after the full moon in autumn.

This year in Berlin, the moon on September 6 (3 days before the full moon) reaches only 24° above the horizon. On September 12 it's 47° above, and that makes the landscape about 78% brighter (if I accounted properly for the light absorbed and scattered by the atmosphere, it would increase that number even further).

I'd love to hear from a historian whether I'm right about the nighttime harvest taking place on the days after the full moon rather than before. If you anyone knows, or can find information about this from a reliable source on the Internet, please make a post in the comments.

Thursday, August 28, 2014

15,000th observation submitted!

The Loss of the Night app project passed another milestone today, with the 15,000th observation being submitted early this morning. The observation was made by an anonymous user in New Jersey, USA under partly cloudy skies. The naked eye limiting magnitude was about 4, with 5 of 7 stars observed.

As I noted when we passed 10,000 observations, most submitted observations are not made under ideal conditions. Sometimes people test or demonstrate the app indoors, sometimes the moon is up, and very often (as in the case of observation #15,000) the sky isn't clear. But through the dedication of our participants, we are continuously building up a record of how skyglow is changing worldwide.

Now the race is on to observation #20,000. To celebrate that milestone, I will again send a holographic postcard to the registered user who makes a complete observation (7 or more stars, no moon, no twilight, no clouds) with the observation number closest to 20,000.

Tuesday, August 19, 2014

New version of the app is coming soon - we need your help this week!

An updated version of the Loss of the Night app is currently in development. The most exciting changes will include:

  • iPhone version!
  • Improved feedback: We fit your data and tell you the estimated naked eye limiting magnitude, approximately how many stars are in your sky, and how consistent your observations were.
  • Smoother behavior: Phones that had problems with an unstable star field should now be fixed.
  • More customization: You can change font sizes and switch the screen brightness between a city/country mode. Pinch zooming will replace the zoom buttons.
  • Better night mode: Removal of gray backgrounds and replacing orange with red in many places.
  • Faster GPS convergence
  • Expanded language support
  • More accurate measurement technique
  • Better set of stars used

We can still use your help with that last point!  The new version has removed stars that are so close together that it's difficult to tell which we're asking for, for example the Pleiades and Alcor. But we have also built in a new list of "easy" stars. These are stars for which you, the users, were able to make decisions on quickly and decisively. We have lots of data about bright Northern Hemisphere stars, but we've had far fewer observations of faint stars, and much less data from the Southern Hemisphere.

The final list of "easy" stars needs to be completed by Monday, so there's one week left for you to help us learn which stars are the best! If you have clear skies at some point this week, please take a moment to go outside and use the app. The more stars you observe, the better, so if you are enjoying yourself, please continue after you've reached seven stars.

This could be you this weekend!

Thank you to everyone who has used the app in the last year!
We appreciate everyone who provided valuable feedback through email or comments!
Dankeschön to our translators!

And finally, if you've told other people about the app, then we can't thank you enough! The more people that take part, the better and more accurate our results will be.

Watch for the official announcement of the new version here in the fall.

Wednesday, July 9, 2014

How to find pictures of cities at night

Astronauts have taken over a million photographs of Earth from the International Space Station. Many of them have been taken at night, like this one of Berlin:

Berlin at Night from the ISS, original image ISS035-E-17210 available here.

NASA has made all of the images freely available through its "Gateway to Astronaut Photography of the Earth". But when you've got a haystack of 1.2M photos and you just want to find the original of the one Chris Hadfield took of Calgary at Night, you could use some help to find what you're looking for.

A group of ISS photo enthusiasts and light pollution researchers have solved your problem by putting together an Atlas of nighttime images of the Earth. This post is a short note to help you use a feature of the Atlas that's not necessarily very obvious from the main page.

When you go to the main page, scroll down to "Gallery of cities at night". Here you can scroll and zoom over the Earth to find a city (like Calgary). When you click on the dot, it will pop up some information about the photo, as well as a thumbnail:

The thumbnail has a link to the photo at the NASA gateway - but if you click on it you'll notice that it's not the one that Commander Hadfield tweeted! The problem is that multiple photos of Calgary have been taken.

While the Atlas website is super for finding cities that have been imaged, it's not what you want to use if you're looking for all photos of a given city. To do that, you want to click below where it says "Original at"

When you click there, you will get to a google spreadsheet that looks like this:

Now click on "Table of data" near the top left, type the city you're looking for in the box at the top left, and then click "Find":

Now you can see more detailed information about the photos, including thumbnails and links to the NASA site if you scroll way over to the right. The photo that Chris Hadfield took is the top one on the list, and now you can go to the NASA site and get the link to the full resolution photograph of Calgary at night.

The last step is to scroll down on the NASA page to the two "view" buttons. Click on the bottom one:

and voila, here is your full resolution image:

Calgary at Night from the ISS, ISS034-E-44268

The images from the NASA site are all free to use, provided you acknowledge the photo source (there is a recommended citation at the bottom of the page). To make it easier for other people to find the photo in the future, be sure to always include the image designator that starts ISSxxx.

If you use the Atlas to find a photo and then publish the photo somewhere, then please also cite this paper: Alejandro Sánchez de Miguel, et al., Atlas of astronaut photos of Earth at night, Astronomy & Geophysics, Vol. 55 no4. August 2014 (in press).

Going forward

The best part about the Atlas website is that it includes three citizen science projects to ensure that future photos are cataloged, and to find other older images "hidden in the dark of the database".

Dark Skies of ISS allows citizens to sort images between different types: Images of cities, images of stars, and other images. It requires no previous knowledge, and is only available online. It is the simplest of the three projects.

Night Cities aims to allow citizens to apply their lay knowledge of local and international geography. The project shows paired images of cities with maps. Project volunteers identify points in the night images and match them to positions on the maps. With this help we can generate light maps of cities.

Lost at Night is the stiffest challenge for citizens with good geographical knowledge of a region. Their goal is to identify which city is in an image without any identification. The position of the cities in this case is only known to within about 500 km.

Note: If this is your first-ever visit to the blog, welcome! The blog is about a citizen science app called "Loss of the Night". We need your help to understand how changes in street lighting technology are changing the night sky. You can read our introduction to the blog here, and instructions on how to use the app here.

There's lots more to see, including:

You can see bring up our entire photo series via this link. Thanks for visiting!