Why does the Sun seem red near the horizon? Why does the Moon do the same? We know the Moon isn’t actually changing colour, and the Sun isn’t either. So what is happening to the light? The first thing to note about the image above is that the size of the Moon doesn’t change, showing that the well-known ‘Moon Illusion,’ where the Moon appears larger near the horizon, is just that – an illusion. The second is of course the gradual change in hue as the Moon rises. The reason for the colour shift really has nothing to do with the Moon...
I love false-colour images. They reveal detail that you can’t see in real life, but they also highlight things in an artistic way. For me it’s an excellent marriage of art and science, and as a communicator it helps me get concepts across in an accessible way. So when I saw the APOD image of Saturn from earlier this week, I had to discuss it. Saturn never has looked this way, and it never will. The colours are vivid and unrealistic, but they show the differences in three distinct but close wavelengths of light on the electromagnetic spectrum. All of...
I’ve been saving this one for a few months, specifically for my Halloween post! This was such an interesting story, it was hard for me to pass it up before. There are ghosts in these distant galaxies! Look at the images above, and see the ghostly green figures. They are ionized Oxygen, helium, nitrogen, sulphur, and neon that has absorbed high energy radiation and slowly re-emitted it over thousands of years. The photoionized gas clouds in the images are tens of thousands of light years outside their host galaxies, so where did this high energy radiation come from? The answer, is...
How often does a star explode as a supernova in the Milky Way? With as many as 400 Billion stars, you would expect it to happen often But stars live a very long time, and most massive stars take anywhere from a few hundred million to a few billion years to reach maturity and explode. Putting all this together gives us a surprisingly human estimate. A supernova explodes in the Milky Way, on average, once every 50 years, or about once per human lifetime. We can still see remnants of great explosions that happened long ago, still expanding into the...
Auroras on Earth are caused by the ionization of atoms high in the atmosphere near the north and south magnetic poles. The solar wind flies toward the Earth and this harmful radiation is blocked and funnelled by our magnetic field, creating harmless, beautiful glows that remind us how close we came to total destruction, but were saved by our planet. Do other planets have auroras? Certainly! Jupiter and Saturn do, and even moons like Ganymede can have auroral activity. It really depends on the magnetic field. So how does a planet like Mars, with no magnetic field, have auroras? This...
For Christmas I was given a green 200 mW laser! A couple of AAA batteries later and the laser can point out any star or object in the night sky, with the beam clearly visible the entire way up to infinity. Its the epitome of an Astronomer’s toolkit, at least in my eyes, and it got me thinking about all the amazing things you can see in the sky right now. It also makes me feel like I’m brandishing a light saber, and sadly it’s about as close as I’ll ever get. First off, Venus is back in the evening...
I’ve seen a lot of lovely images from the Spitzer Space Telescope. It takes infrared images and can see the fine structure of galaxies, where stars are forming and where they are not forming. The photos paint a picture of the history and evolution of a galaxy. The latest image released last week shows some amazing features. The Cyan light in the image is a combination of blue and green coloured light representing infrared wavelengths of light at 3.4 and 4.5 microns. This wavelength shows the stellar population in the galaxy. The red light is representing dust features that glow...
