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What do astronomers look at, and how? Let's start here, in our






Gallery of Astronomical Images.


Some of these images  may seem strange and hard to understand, but by the end of this tour, you'll know what  astronomers see in each one.

1.The Sun in EUV 2.The Sun 3.The Sun in x-rays

Here are 3 images of our nearest star, the sun. Why do you think they look so different? What do you think they  show? Each one is made with different type of light: 1. extreme ultraviolet, 2. visible, and 3. x-ray.  All these images were made by telescopes orbiting the Earth in satellites.



4. If you looked at the planet Jupiter through a good-sized optical telescope above the Earth's atmosphere, it might look like this color-corrected image.

5. But another type of telescope, at the NASA Infrared Telescope Facility (IRTF) in Hawaii, made these images of Jupiter: Why didn't we see the rings before?. What does infrared mean? 

6. This infrared image shows the impact sites of several pieces of the comet Shoemaker-Levy 9, which bombarded Jupiter with its fragments after breaking up in the giant planet's gravitational field in 1994. The impact sites are white because the are locations of intense infrared radiation (infrared = "heat" to you and me).


  5.Jupiter in infrared


6.Jupiter with SL/9 impacts

7. Shoemaker/Levy 9 impacts on Jupiter in x-rays 


7. Still another telescope, on board a satellite called ROSAT, made this image of Jupiter after some of the Shoemaker-Levy fragment impacts.  This is a false-color x-ray image. The black and red spots are emitting fewer x-rays than the green or yellow areas.


Visible light image of Io shows it is pocked with craters8. Volcanic eruptions on Io in visible light. Io is one of the moons of Jupiter and is known as the most volcanically active object in our solar system. Io was discovered by the scientists Galileo and Marius in 1610 (more than 300 years ago!) 


9. Volcanic eruption on Io shows up in the infrared10.1 week later, the eruption is subsiding 9,10.Two infrared images of a volcanic eruption on Io - one of Jupiter's moons. The second image, taken seven days after the first image, reveals that the eruption has decreased in intensity.

11. At right we have a false color image of Comet B2 Hyakutake from NASA's Extreme Ultraviolet Explorer (EUVE) satellite. Various types of light can be "selected" by having light pass through a metal or plastic foil filter.  The light for this image passed through a filter which allows only light with wavelengths of 70-90 Angstroms to go through. 


11.Comet Hyakutake nucleus  in Extreme Ultraviolet


The EUV light from the moon 12.


12. Because it has no atmosphere to absorb these wavelengths, the moon can reflect Extreme Ultraviolet light. Where do you think the EUV light in our solar system comes from?

13. This is a very dense star cluster near the center of our galaxy.  In a few million years, gravitational forces will tear it apart, but for now it contains some of the most luminous stars in the galaxy. Yet, this cluster is not visible because of dust near the galactic center. How was this picture taken?  In x-rays? UV?


  Milky Way star cluster


14. Near infrared image of the disk of the Milky Way

14. Near infrared light from the central disk of the Milky Way. Most of the emission at these wavelengths is from relatively cool giant stars in the disk and bulge of the Milky Way. Interstellar dust does not strongly absorb these wavelengths.


15,16. Two images showing parts of the center of our galaxy in x-ray wavelengths at different resolutions.


  Xxx-ray light from the Milky Way center.

 16. Why do you think they are different colors?

Milky Way center in x-rays

17. In visible light, most of the disk of the galaxy is obscured by dust.

Milky Way center in visible light.

18. But the center of the galaxy appears quite bright (red) in this 
gamma ray image.

 Milky Way's disk in gamma rays  

A radio image of a structure at the center of our galaxy. 

19. Radio wave image showing an Arc at the Galactic Center.
This image shows the spiral galaxy NGC 4736, seen through an ultraviolet filter on top with a visible light image on the bottom.  Click the image for a bigger, more detailed version. 

NGC4736 in UV and visible; a nice, normal spiral galaxy, but it has as least two personalities.

20. This nebula is one of the regions of recent star formation nearest to our solar system (300,000  light years away). The nebula is a giant gas cloud illuminated by the brightest of the young hot stars at the top of this visible light picture.

Nearby star formation region


The hourglass nebula21. Hourglass nebula around a dying star. This is a visible light image of MyCn18 - a planetary nebula located about 8,000 light years away from Earth.

Geminga pulsar in gamma rays

Gamma ray image showing the pulsar Geminga (above and left of center) and the Crab nebula, two bright sources of gamma rays.  Both gamma rays and x-rays are very high-energy.  Do you  know why?

This is a gamma ray image of the Orion molecular cloud complex, also called the Orion nebula. A nebula is a cloud of gas and dust where new stars may form.

Cygnus A radio source From the other end of the wavelength spectrum, this radio image shows the extra-galactic Radio Source Cygnus A.
This is an old supernova remnant in the constellation Cygnus the Swan. It is called the  Cygnus Loop or "Veil Nebula" and is the remains of a star which went supernova (exploded) about 150,000 years ago. The hot gases ejected by the supernova have rammed into surrounding interstellar matter, which is now visible in the ultraviolet as broken, wispy, nebulous rings.  Cygnus supernova remnant

 Supernovas are interesting in almost any light.  They start off tremendously hot, emitting huge amounts of radiation, from infrared to gamma rays. Then, over the millenia, they gradually cool.  As the temperature of a supernova cloud declines, more of the radiation moves to longer wavelengths.  Even after most of the remaining visible glow is obscured by dust, these remnants still radiate strongly in infrared and radio.  Further collisions with matter (as with the Veil Nebula) and the remaining neutron stars may also continue to put out high-energy ultraviolet and x-rays.  

Another example: the Crab Nebula is a much-studied and supernova remnant that has a secret at its center...

Crab nebula in radio
Its radio portrait shows only the cooling gaseous cloud.

Crab Nebula in Infrared
This image made from infrared light has a clue.  Can you find it?

Crab Nebula, visible light
In visible light, the nebula is beautiful, but appears to be hollow.
Crab Nebula in gamma rays
But when we look at an image from highly energetic gamma rays, we can see there's a point source at the center.  This is the "dead star" that gave rise to the nebula when it exploded.
The cloud of debris hides an exotic neutron star called a pulsar, which rotates rapidly, sending off high powered x-ray beams like a lighthouse. 

These X-ray images images show the surrounding cloud  with the x-ray beam pointed away from Earth (left) and towards Earth (right). 

Crab Pulsar--jet pointed awayCrab pulsar, jet pointed toward Earth


Crab Nebula, Chandra x-ray image shows polar jets

Amore recent x-ray image from the Chandra space observatory is even more dramatic. Here you can actually see the jets of x-ray emitting gas coming from the pulsar's magnetic poles.
Here's a radio wave image of an old supernova remnant in the constellation Casseopiea.  The bright pink areas show the outer shell of debris, still glowing at long wavelengths.

This ultraviolet image of the spiral galaxy M101 is from the same ultraviolet telscope as the Veil Nebula image above.  It shows giant star formation regions as bright areas of hot gas and dust.

M 101 galaxy in UV shows star formation in spiral arms.
map of the cosmic mictrowave backgroun Finally this image shows microwave background radiation which is a remnant of the Big Bang origin of the Universe. Its discovery was the first major evidence to support that idea.  The image is a map of the entire sky.

Light Basics Types of Light Light Gallery The EM Spectrum

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