REPOST: This was originally written in 2007 but is being reposted because of some discussion it generate elsewhere.

There is a lot more to the universe than the light you and I can pick up with our eyes and brains. Although its a shame that we can’t see them naturally we can use technology to reveal the wavelengths of light normally invisible to us. Visible light is only part of the electromagnetic spectrum (a very small part) and I thought it would be interesting to see some familiar objects in unfamiliar ways.

The electromagnetic spectrum is usually split into seven parts: the radio, microwave, infrared, visible, ultraviolet, x-ray and gamma ray. You can find a good schematic of the EM spectrum over on Wikipedia. We obviously see things in the visible, but some creatures, such as bees, see some of the ultraviolet (one reason there are so many purple flowers). Here is a picture of a Geranium in the visible and then the UV. You can find more images like these, for all kinds of flowers over at this website.

But this is an astronomy blog and so here are some objects seen in multiple wavelengths. Some of them may surprise you. First up is the Moon. Here we have it in the radio, microwave, infrared, visible, ultraviolet and x-ray.

The infrared image (top right) shows various bright spots. These are warm areas on the Moon. The brightest spot, in the bottom-center of the Moon is the crater Tycho, which also shows up brightly in the visible and UV images. The X-Ray picture is from ROSAT (bottom-right). Here we see the Moon shown in its quarter phase to highlight that it is only reflecting X_Rays from the Sun and not giving any off itself. The Submillimetre (microwave) image (top-centre) was taken using the SCUBA camera on the JCMT in Hawaii. This is a camera normally used to image dust in nebulae and faint galaxies.

Next let’s look at something more exotic but still familiar, the Andromeda Galaxy. Also called M31, this is closest neighbouring galaxy in the wider universe and is just about visible from a good site. We are seeing this in the radio, microwave, infrared, visible, ultraviolet and x-ray.

You can really start to see now why observing objects in different wavelngths can tell us something about them that we didn’t know before. The different details in each image are coming from different parts of the galaxy. In the top-center image, which is taken at 175 micrometres, we are seeing the dust lanes between stars in the galaxy. The X-Ray image in the bottom-right shows us only the extremely energetic objects, which as we can see, are located predominantly toward the centre.

Another easy to spot object, which you may know of is M45, also known as the Pleiades or Subaru. Once again here it in the radio, microwave, infrared, visible, ultraviolet and x-ray.

The most impressive image here in my opinion is the X-Ray image from ROSAT (bottom-right). It looks to me like something from Doctor Who. It is also interesting to note that M45 doesn’t show up as much in radio frequencies. In the top-centre image we can see only some of the stars. This is because M45 is a young cluster and some of the surrounding dust still obscures the stars in this far-infrared image.

I thought I’d save the best til last: here is the Earth. Now its tricky to get pictures of our own planet - because we’re on it. We’re lacking in any good radio images of the Earth because you can do radio astronomy perfectly well without putting telescopes in space. However I really like these images because they really took me by surprise. In order, these images show the Earth in infrared, visible, ultraviolet, extreme-ultraviolet, x-ray and gamma rays.

The first image shows the infrared emission on the Earth from water vapour. Like the two UV images, this picture is from an extensive network of Earth-observing satellites that are attempting to investigate how our planet operates. Tectonics, oceanography and climate change are just three of the many topics being studied to ever-more depth by NASA, ESA and researchers the world over. The X-Ray image (bottom-centre) shows an aurora on the Earth’s north pole. Other than this high-energy interaction between the atmosphere and the Sun, the Earth seems to be invisible at this wavelength.

Finally we have the gamma ray image (bottom-right). What you’re seeing here are extremely high-energy particles, mostly from outer space, reflecting off the Earth’s atmosphere. The edge of the globe is seen to be much brighter than the center because cosmic rays hit the atmosphere at a shallow angle and are more likely to create detections. There is an imbalance btween the East and West due to the Earth’s magnetic field, which is asymmetrical.

I hope you’ve enjoyed this little collection, if you know of any other cool multiple wavelength images - astronomical and otherwise - then please leave a comment with a link.

Continuing my series of posts regarding Google Sky and Google Earth, here is a KMZ file that will let you find some of the prominent and interesting space telescopes and satellites on Google Earth. This file includes real-time position tracking and 1 hour flight paths for:

• Swift Gamma Ray Mission (NASA)
• RoSat (NASA, UK, Germany)
• CoRoT (CNES, ESA)
• GalEx (NASA)
• COBE (NASA)
• IRAS (NASA, UK, Netherlands)
• Envisat (ESA)
• Hubble Space Telescope (NASA, ESA)
• International Space Station (Many)

This KMZ file splits down into several separate files so you can chose to select or deselect any and all of the above objects. Clicking on the satellite or telescope’s icon brings up information about that object with links to more information. Screenshots below for those who like that sort of thing.

To see more Google Earth satellite files check out the general Satellites on Google Earth post and the Chinese Space Debris post. As always, suggestions are welcomed in the comments section. For example, I had created a time-slider dependent satellite tracker but it just ended up being really annoying. Would that be something people would want? Also, as mentioned in a previous comment, I am in the process of creating a tracker that uses a Sketchup model instead of an icon. All thoughts welcome, have fun playing with these.

I love NASA’s Astronomy Picture of the Day, known to its friends as APOD. So to honour that Great website, which has been running for more than a decade, I here present my own personal top ten list of APODs. They may not be quite the same as anyone else Top Ten but they represent some of the best things about the APOD site as well as being some of the most impressive images.

10: Mars Then and Now

Two images of Mars taken over 100 years apart. The first was drawn by Eugene Antoniadi in 1894, the second is from Hubble during the close approach of Mars in 2003. Its interesting to see what they got right and what they got wrong. Notably the extensive system of Martian Canals, which Percival Lowell was so adamant existed and proved the presence of Martians.

Credit: Tom Ruen, Eugene Antoniadi, Lowell Hess, Roy A. Gallant, HST, NASA
More Historical APODs - Yuri Gagarin, Voynich Manuscript

9: The Surface of Europa

Back in January 1998, when this image appeared on APOD, the Galileo Mission was still sending back amazing new pictures from Jupiter and it’s Moons. This was around the time I first discovered APOD and have been checking it ever since.

Credit: Galileo Project, JPL, NASA
More Groundbreaking APODs - Shadow of Saturn, Pluto’s True Colours

8: Bubble vs Cloud

This 2005 APOD captured my imagination for some reason. You can really see a three-dimensional effect in this beautiful picture. The actual title of the image is ‘ NGC 7635: The Bubble Nebula’ but the phrase ‘Bubble vs Cloud’ stuck with me somehow. It just got me thinking about how dynamic all of these giant objects are, even if we will never see it for ourselves.

Credit: Russell Croman
More APOD Nebulae - The Eagle Nebula, Orion Nebula, Carina Nebula

7: Close Up of the Face on Mars

After years of being told by people that there was a giant human face on Mars that an ancient civilisation had once created it was satisfying to see it for real and notice that ‘hey, there is no face’.

Credit: Malin Space Science Systems, MGS, JPL, NASA
More Debunking APODs - Equinox Eggs, Green Flash, The Moon Illusion

6: Binary Black Hole

This composite image shows the x-ray in blue and the radio in pink. You can see two black holes in the middle, which are each streaming out relativistic particles. These two objects are 300 million light years away! This APOD from April 2006 was the first time I had ’seen’ a black hole in any convincing sense.

Credit: X-Ray: NASA/CXC/D.Hudson, T.Reiprich et al. (AIfA); Radio: NRAO/VLA/NRL
More Unseeable APODs - Dark Matter, Neutrinos

5: A Sun Pillar

One of the things APOD does best is show not only planets, nebulae and other distant objects, but also some cool, Earth-bound astronomical tit-bits. This Sun Pillar is created by ice crystals in the atmosphere. They are best seen during the colder months.

Credit: Stan Richard
More Earthbound APODs - Giant Machine, Lenticular Clouds, Aurora

4: Earthrise

This is a Christmas Eve APOD from 2004. The site has never been afraid to put up historical pictures or to be a little poetic when it feels like it. This image was taken around ChristmasEve when the three Apollo 8 astronauts were orbiting the Moon. They returned safely on December 27th, in time to see the 1967 Sunrise back on the Earth.

Credit: Apollo 8, NASA
More Poetic APODs - Martian Love, Huygens Discovery, Liberty Bell

3: Hyperion

Like a 250km sponge, Saturn’s Moon Hyperion is covered in odd craters and has a density so low that it has led researchers to assume it made up of vast deep caverns. This image shows the moon in excellent detail. The images on APOD have steadily improved with improving technology over the years and this amazing Hyperion picture is a great example.

Credit: Cassini Imaging Team, SSI, JPL, ESA, NASA
More High Resolution APOD - Annual Eclipse, Mars HiRISE, ISS Silhouette

2: Blue Lagoon

Sometimes you see a picture that just takes your breath away. This APOD was just such a picture. This wonderful Lagoon Nebula picture, which to me, looks like a painting, was not taken by Hubble as many might think but by a 20″ telescope on Earth.

Credit: Russell Crowman
More Artistic APODs - Moon from Space, Sombrero in IR

1: Venus Near the Moon

Not a grand finale in one sense, but a stunning picture never-the-less. What APOD has always done best are images like these, taken not by massive telescopes but by normal observers with affordable equipment. The stuff you can see with your eyes and appreciate instantly without explanation. This crisp, detailed image of Venus near the Moon sums up what so many of us like about astronomy, and why the subject remains accessible to just about anyone.

Credit: Jay Ouellet
More Backyard APOD - Moon Animation, Station and Shuttle, Blue Moon

So thank you to Astronomy Picture of the Day for many years of service to the internet. May you long continue to wow us on a daily basis.

APOD is also available as a Google Homepage Gadget, a Netvibes Module, an Apple Dashboard Widget, a Wordpress Widget, a Yahoo Widget, a Windows Vista Gadget , as a Twitter Feed and probably loads more.

If you have other APODs you think deserve attention, leave a link in the comments thread so we can all see.