Space Telescopes

The biggest problem astronomers have with earth-based telescopes is that our very atmosphere that protects humans from harmful solar radiation also prevents study of these forms of radiation that are emitted from stars. Our atmosphere allows visible, infrared, some UV, and radiowaves to penetrate, but all gamma, x-ray, most UV, and submillimeter waves cannot penetrate. Neutron stars emit x-rays, collapsing white dwarfs emit gamma rays, and energetic O class stars emit UV light. In order to study stars and galaxies at all wavelengths, specially designed telescopes need to be launched above earth's atmosphere. The most famous space telescope is the Hubble Space Telescope, seen in the image below. This telescope has a primary mirror of 2.4 meters in diameter, and was launched into orbit April 24, 1990. The overall telescope is as big as a bus, and the incoming light can be directed to a host of different instruments for study. The Wide Field Planetary Camera is responsible for giving us so many interesting photographs which appear in newspapers, posters, and screensavers worldwide. But the telescope also has other instruments which detect light at non-visible wavelengths. Since its launch, a slight error in the primary mirror was discovered, causing early images to be blurred. A successful NASA space shuttle mission corrected the optical error, and astronomers have been thrilled ever since. The telescope itself was never expected to be in service for more than a few years, but a very recent mission by NASA astronauts in early 2002 serviced the telescope, and the Hubble is expected to deliver wonderful science information for many more years. To visit the Hubble website, click on HST, where you can link to a history of the telescope, look as a great image gallery, and learn about the various instruments. To see other nice images collected at the Arizona Site, click on the Helix Nebula image next to the telescope, and to see an alternative Hubble site, click on the telescope image below. Since the reserving of this telescope earlier this year, and the installation of a new camera, the images taken by the HST ought to be the most spectacular ever, and greatly increase our knowledge of celestial events.

Beyond the wonder of the Hubble Space Telescope visual telescope, is the value of being able to observe other wavelengths, provided the telescope is attenuated to those wavelengths. The High Energy Astrophysics organization is dedicated to exploring stars at high energy wavelengths such as gamma, x ray, ultraviolet radiation. The Compton Gamma Ray Observer (CGRO) sent back some incredible images of the Universe as it appears at the gamma radiation wavelength, and has since been replaced by the EGRET. A great place to learn about HEA research is the High Energy Astrophysics Science Archive Research Center (HEASARC) with its links to various space telescopes attenuated to different forms of high energy electromagnetic radiation.

At left is the Advanced X-Ray Astrophysics Facility (AXAF) dubbed the Chandra Telescope, named after a famous Indian astronomer Subramanyan Chandrasekhar. This telescope was deployed July 23, 1999 and is useful for the study of gamma ray emissions from stars that explode when their remnant material reaches a critical mass theorized by Chandrasekhar. You can link directly to the Chandra homepage, and then go to the image collection to see what it sees. You will learn more about gamma bursters, but for now, here is a short introduction. The collapse of white dwarfs, that suddenly exceed a mass limit of 1.44 suns, results in a spectacular detonation and the release of energy beyond your imagination. If two neutron stars in a binary system spiral in toward each other and merge, the release of energy is even greater. These events result in such prodigious gamma radiation that huge parts of galaxies, if not entire galaxies are sterilized from any lifeforms. Clearly, it is a good idea to learn about these events, and attempt to predict if any may occur in the Milky Way, thus threatening us.

The image to the left is the Compton Gamma Ray Observer (CRGO), and is the heaviest scientific instrument ever put into space. The facility has since exceeded its usefulness and reentered earth's atmosphere a few years back, but not before yielding wonderful information about the high energy universe. The latest telescope to observe high energy wavelengths is the Energetic Gamma Ray Experiment Telescope (EGRET). You have to admit ... NASA engineers seem to enjoy making up names for their instruments.

If you want to see images from various HEA instruments, click on the COSSC Image Gallery.

 

 

 

Infrared Astronomy offers many advantages over optical astronomy because stars which are just beginning to form produce light from the friction of their collapsing matter, but only as a glow from the heat of the friction instead of the visible portion of the spectrum. Infrared telescopes can see this material, as well as other regions where gas is glowing and thus learn about the processes that take place in early star formation. I strongly encourage you to check out three fantastic websites about infrared astronomy to learn more about this important tool:

 

 

 

IPAC is the Infrared Processing and Analysis Center, and this site will introduce you to the importance of infrared astronomy

IR Timeline is the site which traces the history of infrared astronomy and offers connecting links to all of the past, present, and future infrared telescope projects.

SIRTF is the newest infrared telescope, and is presently under construction. I had the opportunity to meet several SIRTF team members at an astronomy conference in the summer of 2001.

 

An example of the infrared telescope over optical telescopes is found in these two images of Orion. On the left is the optical image of the familiar constellation, and on the right is the infrared image of the same area/ The bright yellow cloud in the lower center of the IR image is the famous Orion Nebula star factory. Look at what out eyes are missing because we cannot see in the infrared.

Infrared cameras are exceedingly useful because they can see through dust, clouds, and gas. They work because they sense heat radiation. Humans radiate heat at a temperature of 37oC, and according to Wein's Law, we radiate at 9677 nm. An infrared camera attenuated to longer wavelengths would see the heat signature of people as bright objects against a cool background. Snakes use this form of thermal imaging to sense prey. Firefighters uses IR cameras to look for people in smoke-filled rooms. The "Predator" saw the heat signature of Arnold Schwartzenegger, but when Arnold covered himself in riverbank mud, the cool temperature mud hid is body heat from the alien, allowing Arnold to buy some time and figure out a plan to kill the alien.

Finally, space telescopes can look at microwaves, which are inhibited from atmosphere entry. The most famous of these observatory is the Cosmic Background Explorer (COBE) whose job was to explore the Universe at the microwave radiation wavelengths. This is the telescope which yielded fantastic information about the potential origin of the Universe. To see a "slide show" of this famous telescope, click on COBE Slides. You will need Acrobat Reader to view the slideshow.

 

 

 

This telescope has generated images of the deepest part of the Universe, seeing things at such an early age that stars and galaxies had not yet formed. The term "Legacy" seen in the image to your left is quite correct.

Building an observatory on the Moon

All of these telescopes are presently orbiting Earth. There is a new initiative (BBC news) in Washington, DC that is proposing sending people back to the Moon. One of the biggest reasons for returning to the Moon after so many years is the many advantages that an observatory on the Moon would have over observatories on the Earth. One advantage is that astronomers would not have to deal with an atmosphere that blurs the images of faint stars. Another advantage is the Moon has no atmosphere what blocks different wavelengths of the Electromagnetic Spectrum, so astronomers could observe deep space objects at all wavelengths. Finally, astronomers could do meaningful observations 24 hours a day because there is no atmosphere that scatters the sunlight making is possible to study stars while the Sun is out. Click on the image above to see where the drawing came from and some of the ideas behind it.

So ... you have finished looking at space telescopes, learned about optical and radio telescopes, starlight, and the electromagnetic spectrum. I guess the next thing to do is go out to a nice store and buy a telescope or binoculars so you can do some stargazing. Please move forward to Getting Your Own Telescope, or return to Introduction to Light and Telescopes Page, the Syllabus, or the Home page.


| Home | Course Information | Assignments | Teacher Bio | Course Units | Syllabus | Links |