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.
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.