What am I looking at?

Last updated: 5th July 2012

Chromoscope shows you the view of the Universe that we get from Earth. The view is mostly dominated by our galaxy - The Milky Way - which is the band running horizontally across the middle. The direction of the centre of the Galaxy is, appropriately, in the centre of the screen. All the stars, and many of the nebulae you can see are also in the Milky Way. Some of the objects you can see in visible light are far beyond our own galaxy. With other types of light you can see objects far across the Universe and even see light that set off shortly after the Big Bang.

If you don't like reading, you could listen to us talk about Chromoscope on the 365 Days of Astronomy podcast.

Index

The Milky Way

The Milky Way is made up of around 100 thousand million stars but our eyes only let us see a few thousand of the brightest/closest. The image in Chromoscope still only shows you a tiny fraction of the stars in the Milky Way because many are too far away but also because many are obscured by interstellar dust. You can see the bands of dust in our local spiral arms blocking some of the light in that band across the middle.

Visible Light

As we mentioned above, the initial view is that as seen with visible light but taken with photographic equipment with long exposures to allow you to see more detail and fainter objects. Most of the white light originates from stars but you'll also see reddish, nebulous, regions such as Barnard's Loop in Orion which are glowing clouds of hydrogen gas.

By pressing 'L' on your keyboard you can turn on the constellation labels to help you orientate yourself.

Some common questions:

Gamma-ray Light

The Fermi Gamma-ray Space Telescope, formerly GLAST, reveals the high-energy sky between 10 keV and 300 GeV. With Fermi, astronomers can study black holes and other highly energetic events in the universe. Physicists can use Fermi to study subatomic particles at energies far greater than those seen in ground-based particle accelerators. Also, cosmologists gain valuable information about the birth and early evolution of the Universe.

X-ray Light

The Roentgensatellit (ROSAT) was a joint German, US and British X-ray astrophysics project. ROSAT carried a German-built imaging X-ray Telescope (XRT) that allowed researchers to probe high-energy x-ray activity in the universe between 0.1 to 2 keV. ROSAT also performed an all-sky survey which revealed the structure of our galaxy in this energetic type of light.

Some common questions:

H-alpha Light

Hydrogen is the most abundant element in the universe and there is plenty of it in our own Milky Way galaxy. Hydrogen alpha (H-alpha) refers to a specific energy emitted by hydrogen atoms and seen as red light with a wavelength of 656.3 nanometres. The h-alpha part of the Chromoscope comes from several sources including WHAM, The Wisconsin H-Alpha Mapper, and SHASSA the Southern H-Alpha Sky Survey Atlas. WHAM is funded by the American National Science Foundation.

H-alpha light allows us to trace out the location of hydrogen gas in our galaxy.

Near infrared Light

Far infrared Light

The Infrared Astronomical Satellite (IRAS) was a joint project of the US, the UK and the Netherlands. The IRAS mission performed an unbiased, sensitive all sky survey at 12, 25, 60 and 10 µm. IRAS increased the number of cataloged astronomical objects by about 70%, detecting about 350,000 infrared objects.

IRAS discoveries included a disk of dust grains around the star Vega, six new comets, and very strong infrared emission from interacting galaxies as well as wisps of warm dust called infrared cirrus which could be found in almost every direction of space. IRAS also revealed for the first time the core of our galaxy, the Milky Way.

Microwave Light

This image of the sky, as seen in microwaves (30-850 GHz), was released by the European Space Agency's Planck satellite in 2010. Light at these wavelengths is caused by a number of processes. The lower frequencies are due to electrons spiralling in magetic fields whereas the higher frequencies are emitted by cold dust.

Across the middle of the image you can still see the Milky Way. Most of the filimentary structure you can see are clouds of cold (roughly -250°C) dust that exists between the stars. Up to the right of the centre you can see Centaurus A. With visible light, Centarus A looks like a relatively unassuming faint star but in fact it is an active galaxy with two radio jets (seen as pink here) coming from the supermassive black hole at its heart.

Away from the bright band of the Milky Way (the filamentary stuff), you can see mottled red/yellow areas. This is actually the most distant light we can see as it set off only around 380,000 years after the Big Bang.

Radio Light

408MHz, a relatively low radio frequency, allows us to measure light produced by electrons travelling close to the speed of light and spiralling in magnetic fields. The full-sky map produced by astronomers in Germany, the UK and Australia (1981-1982), combining data from 3 large (60-100m) radio telescopes around the world, shows strong emission from the disk of our galaxy. Away from the disk, large features are also seen, which are thought to be remnants of nearby ancient supernovae. The map is also dotted with distant radio galaxies.

Some common questions:

Questions

If you have questions about Chromoscope, ask us on Twitter @chromoscope.

Why do things look different in different types of light?

Different types of light come from different physical processes. For instance, very hot things glow white - they producing colours across the entire visible spectrum. This is called thermal emission because it is due to temperature. All objects with a temperature give off light. Objects that are too cold to be seen glowing with visible light are glowing with infrared light. Other types of light come from changes in the internal structure of atoms, from electrons spiralling around in magnetic fields, and even from collisions of very energetic sub-atomic particles. By comparing how much light of each type we can detect, we can understand the temperature, magnetic field, and chemical composition of the object that is giving off the light.

Are these colours/colors real?

Simply put, these images show you real objects and structures in the sky. The colours/colors are "representative" - we had to choose a colour of visible light to display them with otherwise your eyes wouldn't be able to see them. We chose green for X-ray light but could have equally chosen yellow, blue, red, or gray. Unlike photoshopping an image, this isn't changing the structure you can see. What really matters is how the brightness varies across the sky. Comparing the structures between the different types of light tells you about the physics of what is producing the light.

Why is the Galaxy a straight line? Isn't is round?

From outside, out galaxy would look a bit like two fried eggs placed back-to-back. It has a disk with a bulge towards the centre. Our solar system is roughly two-thirds of the way out from the centre. As we are in the disk (sitting in the white bit of the fried eggs) it looks as though it surrounds us in a line around the sky. Looking at the line is to look along the disk so you are mostly seeing the egg white that is just next to you (the local stars/dust). Looking away from the line means you are getting an unobstructed view out of the disk so you can see things beyond.

What are the lines?

As you zoom in you may see some odd features such as bright lines, or circles with crosses in them. The bright lines are usually the tracks of Earth-orbiting satellites that just happened to pass through the view when the original images were being taken. They are bright because they are reflecting sunlight down to the ground and are lines because the satellite moved during the long exposures. Sometimes these lines are dotted because the satellite is spinning and reflecting different amounts of sunlight as it moves. They may also appear to stop suddenly and that is because the satellites were only in the way of the telescope for one exposure. If you look up on a dark night you can occasionally see satellites with your own eyes.

Are there space-spiders?

The circles with dark crosses/spiders in them are actually problems with the original images and are not astronomical. If you look at a few of them you'll notice that they are always near bright stars. In fact, they are stray reflections of the bright stars within the telescope that took the image. As the stars are so bright, some small amount of the light can bounce off the internal surfaces of the telescopes. The result is that the bright star creates a tiny image of the inside of the telescope itself! The spider/cross parts are actually shadows of the support legs that hold the secondary mirror in place. There may be space-spiders in the Universe but these aren't images of them!

What are the tears/gaps in the X-ray view?

In the X-ray you can see the plane of the Galaxy but you will also notice some striking black arcs. Don't worry, they aren't holes in the Universe being ripped open by creatures from another dimension! They are actually just gaps in the survey.

The ROSAT spacecraft spun around imaging the sky in strips. Over many months these strips would build up into a full image of the sky. Unfortunately, on a few days, the data from the spacecraft were lost. Given the way the spacecraft imaged the sky, it couldn't go back to see those missing parts before the end of its mission.

What's the huge white spot on the far right on the arm while using X-ray?

This is the Vela Supernova Remnant. It is what remains of a massive star that is thought exploded over 11,000 years ago in the direction of the constellation Vela. The centre of that exploding star collapsed inwards to create a neutron star which we know as the Vela pulsar. A neutron star has around the mass of our Sun squashed into a region of space equivalent to a large city. It is very dense and very extreme. It emits two radio beams from its magnetic poles.

What's with the bright flares in the radio spectrum on the left?

In radio light (and also X-ray light) you'll notice a large arc rising up from the plane of our galaxy (the bright region across the middle). When the first radio surveys of the sky were made this was a total surprise to astronomers as you can't see it with visible light. It is called the North Galactic Spur and is thought to be the remnant of an ancient supernova explosion that occured somewhere in the neighbourhood of our solar system.

The North Galactic Spur is a good example of why it is important to view the sky with lots of different types of light.

If you have more questions about astronomy we recommend this book.