Showing posts with label moon. Show all posts
Showing posts with label moon. Show all posts

Tuesday, September 29, 2015

Europe during last night's lunar eclipse

Yesterday morning the moon passed into the Earth's shadow. The period of totality happened to occur just as the Suomi NPP satellite was passing over Europe and northern Africa. Suomi carries the Visible Infrared Imaging Radiometer Suite (VIIRS), which includes a "Day Night Band" which is the best (and only) full-Earth nighttime imaging sensor. That makes for a very pretty picture:

Image and Data processing by NOAA's National Geophysical Data Center,
cropped and enhanced by me. This image can be used with credit to NOAA and me.

Blogger has limits on the image size, so you probably want to see this higher resolution version (the full resolution version is hundreds of Mb, if you want to download it you can for the next two weeks here).

When the moon is full, Suomi can see clouds and land extremely well, and oceans and lakes appear extremely dark. The brightest spots are artificial light from human settlements. For example, check out this zoom in of the Nile delta, Israel, and the Gulf of Suez from the same image:

Image and Data processing by NOAA's National Geophysical Data Center,
cropped and enhanced by me. This image can be used with credit to NOAA and me.

But during the eclipse, the moonlight is temporarily gone, and the areas of Europe and northern Africa were plunged into starlight, which is just a bit too dim for good imaging from the sensor. Luckily for us, much of Europe had clear skies, meaning that we can see the city lights shining through!

Nearly a year ago I posted an image of a lunar eclipse over North America that is maybe even cooler because of the different gradient in moonlight.

Friday, October 10, 2014

Moon phase calendar for 2015

Loss of the Night app user Andrew Cool from Australia has once again produced his very cool calendar of the phases of the moon in 2015:


You can download his original images in high and low resolution on his SkippySky website.


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, and all of our posts about the moon here. Thanks for visiting!

Thursday, October 9, 2014

Last night's lunar eclipse, viewed from space

Each night, an instrument called VIIRS DNB takes visible band images of the entire Earth. When the moon is up, it's really easy to see the patterns of the clouds, and when the moon is set you can basically only see the artificial light from cities. But what happens when you have a lunar eclipse? This:

2014/10/08 lunar eclipse viewed by VIIRS DNB by Christopher Kyba & NOAA
is licensed under a Creative Commons Attribution 4.0 International License.
Based on a work at http://ngdc.noaa.gov/eog/viirs/download_ut_mos.html.
Image and Data processing by NOAA's National Geophysical Data Center.

As the Earth's shadow darkened the face of the moon, there was progressively less light for DNB to be able to see land, clouds, and sea. As a result, with each pass of the satellite the image gets darker. The satellite takes about an hour and a half to go around the Earth, so the effect lasts over 2-3 passes. Since we don't have a geostationary satellite capable of imaging the Earth in moonlight, it's not yet possible to produce an video, like this one of a solar eclipse.

For the next several days, you can access the full (giant) resolution image from NOAA. You can get an in-between resolution image from my personal webpage.

If you'd like to see images of hurricanes imaged by VIIRS DNB with moonlight, follow @DanLindsey77 on twitter:

Note for new visitors: This blog is about the Loss of the Night citizen science app, which lets regular people measure how bright the sky is by looking at stars. The goal of the app is to track how the brightness of the sky changes as LED lighting is implemented worldwide. The app is free, and can be downloaded for Android phones. An iPhone version is in development and will come out soon.

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 right 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.

Monday, April 21, 2014

Representations of the moon in art

It's day 2 of International Dark Sky Week, and the moon is fading towards a crescent, visible only in the early morning. That means that it's a great time to use the Loss of the Night or Dark Sky Meter apps, or to contribute to GLOBE at Night using the regular webapp. To celebrate the crescent moon, here's a post about depictions of the crescent moon in art.


If you saw a painting of a scene that included a coniferous tree filled with blossoms or fruit, it would be incongruous, and unless it was done intentionally it would probably somewhat spoil the painting. Similarly, if shadows are drawn incorrectly it can distract from the image, which is why shading is taught to aspiring artists early on. Unfortunately, these lessons often don't extend to the shading of the moon, and representations of the moon in contemporary art are often (or more likely usually) incorrect. (Check out these tips to learn how to draw the moon correctly!)

The moon is most often depicted as a crescent, and there are two problems that frequently pop up. The first is that the real crescent moon is lit from the very top to very bottom:

Crescent-moon
Crescent Moon by Thomas Bresson from the Wikimedia Commons

Many artistic depictions of the crescent moon extend considerably past the top and bottom of the moon:

Golden Crescent Moon

Golden Crescent Moon by Dcubillas from Wikimedia Commons

The second problem has to do with the orientation of the moon and the surroundings. If you think of the crescent moon as an arrowhead, it always points towards the sun, and because the crescent moon occurs near the new moon, it's always close to the sun in the sky. So a "D" shaped crescent moon is low in the sky and sinking after sunset (in the Northern Hemisphere), and a "C" shaped crescent moon rises shortly before the sun. (Apparently, right handed artists prefer to draw the C shape, making their images look like early morning rather than evening).

Once you know a bit about the moon, incorrect depictions jump right out at you, and can spoil the art. For example, in the generally excellent "Conqueror" series of books about Ghengis Khan, the moonrise or moonset were often incorrectly described, which isn't so pleasant in "historical fiction". In one particularly bad case, the crescent moon rose shortly after the sun set (not possible!), and the opposing general took it to be a good omen. Since the plot could hang on a detail like this, it's unfortunate when more care isn't taken.

I have suspected for quite a while that before the advent of electric lighting, people would have been more familiar with the comings and goings of the moon, and it's made me wonder if depictions of the moon in art are were more likely to be correct in the past.

Over Easter, I visited St Mary's Church in Stralsund Germany to listen to an organ concert. While we waited for the concert to begin, I took photos of two of the church's paintings that caught my eye because of the presence of the crescent moon. The first photo shows a burial at sea:

"Seebestattung" (Burial at sea) - unknown artist, ca 1900, oil on canvas
The crescent moon is correctly depicted: it points towards the sunset in the West. We can tell it's sunset and not sunrise because the painting most likely represents a burial in the Northern Hemisphere. Since the moon is never near the northern horizon, it follows that the right hand side of the painting must be the West.

I don't know the name or any details of the second image:


Here you can see that the crescent moon is again correctly depicted, with the lit part running exactly from top to bottom, and the moon "pointing" straight to the sun. Some artistic license is used here, because stars are shown with the moon while the sun is up, but (I think) the two sides represent before and after Adam and Eve ate from the tree. (It's also interesting to me that living in Eden is depicted as being in the night, while being cast out of Eden is under the sun.)

Of course, artists are free to depict the moon (and pine trees) any way they want. But if it's going to be depicted differently from nature, artists should be aware that some segment of the population will note the incongruity, and it may spoil the work for them.

Wednesday, November 20, 2013

Moon phase calendar for 2014

Loss of the Night app user Andrew Cool from Australia has produced this very cool calendar of the phases of the moon in 2014:


A higher resolution version is available here, and you can buy the poster on zazzle. (I got a coffee mug, and I don't recommend it because Zazzle's printing resolution on the cup is too low.)

Update: Andrew has made 2015 moon phase calendars with different designs and for the Northern and Southern hemispheres.

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, and all of our posts about the moon here. Thanks for visiting!