24.2 – Tools for Studying Space

Do Now How does a refracting telescope differ from a reflecting telescope?

Do Now How does a refracting telescope differ from a reflecting telescope? Glass vs. mirror; refracting = chromatic aberration and reflecting = much clearer.

Key Words Distort Optical Spectacular

Vocab Words Refracting Telescope Reflecting Telescope Chromatic Aberration Radio Telescope

Studying Space Optical Telescopes Refracting Telescopes Reflecting Telescopes Detecting Invisible Radiation Radio Telescopes Space Telescopes Hubble Space Telescope Special Purpose Telescope

Refracting Telescopes Galileo was the creator and first user of this type of telescope. His version was able to magnify objects 30 times. Uses a glass lens to bend or refract light.

Refracting Telescopes The most important lens in a refracting telescope, the objective lens, produces an image by bending light from a distant object so that the light converges at an area called the focus, or central point.

Refracting Telescopes If a telescope is used to examine an image directly, we then use a second lens, called an eyepiece. The eyepiece magnifies the object that the objective lens shows. The eyepiece shows details not shown by just the objective lens. Refracting telescopes were used greatly with early astronomy but it had one major flaw, an optical defect, called chromatic aberration. When the image is weakened and there is a halo of color around it. When blue light is in focus, a reddish halo appears. When red light is in focus, a bluish halo appears. This cannot be eliminated completely, but can be greatly reduced by using a second lens made of a different type of glass.

Reflecting Telescopes Newton was bothered by chromatic aberration so he built telescopes that reflected light from a shiny surface – a mirror. Because reflected light is not dispersed into its component colors, the chromatic aberration is avoided. Reflecting telescopes use a concave mirror that focuses the light in front of a mirror, rather than behind it, like a lens. The mirror is generally made of glass that is finely ground and coated with a highly reflective material, usually an aluminum compound.

Reflecting Telescopes There are major advantages to using a reflecting telescope. One disadvantage is that the secondary mirror blocks some of the light entering the telescope.

Optical Telescopes Both refracting and reflecting telescopes have three properties that aid astronomers in their work: Light-gathering power Telescopes ability to intercept more light from distance objects, thereby producing brighter images. Resolving power Sharper images and finer details Magnifying power Ability to make an object larger.

Invisible Radiation There are many things out in space that can not be seen with an optical telescope and so we need other types of telescopes to see those waves. These telescopes extend the limits of our vision. These telescopes are called radio telescopes. They detect mostly radio waves out in space. A radio telescope focuses the incoming radio waves on an antenna, which absorbs and transmits these waves to an amplifier, just like a radio antenna.

Invisible Radiation Radio telescopes have poor resolution, making it difficult to pinpoint a source, so that is why there are always pairs or groups of telescopes to reduce this problem. Have revealed spectacular events like the collision of two galaxies, also quasars and pulsars. There are some advantages to radio telescopes over optical telescopes such as: Being able to view 24 hours a day Not affected by the atmosphere No protection dome needed, like an observatory Can see through things optical telescopes can’t Interstellar gas clouds

Space Telescopes Space telescopes orbit above Earth’s atmosphere and thus produces clearer images than Earth-based telescopes. These telescopes are not affected or distorted due to Earth’s atmosphere.

Hubble Space Telescope The first space telescope, built by NASA, was the Hubble Space Telescope. It was first put into orbit in April 1990. This telescope has 10 billion times more light-gathering power than the human eye. It has been able to provide us with more information on our solar system, other planets that orbit other stars, the birth of stars, black holes, the age of the universe, and the expansion of the universe. Hubble and many Earth-based telescopes have detected more than 140 extrasolar planets. http://www.nasa.gov/mission_pages/hubble/main/index.html

Special Purpose Telescopes We have built a lot of telescopes that are used for a specific and special purpose other than the Hubble. To study X-rays we use the Chandra X-Ray Observatory To study infrared we use the James Webb Space Telescope Voyager is used to go beyond the furthest points we have traveled to. With more advances in technology the more we attempt to understand about space. http://www.nasa.gov/missions/current/index.html

Group Challenge Question Why would the moon make a good observatory?