Chapter 3 Optical telescopes, radio telescopes, and other technology advances our understanding of space. An array of the National Radio Astronomy Observatory (NRAO), which operates radio telescopes across the western hemisphere and is used by international scientists.

3.1 Seeing the Visible Optical Telescopes Lenses or mirrors gather and focus light. The larger the lens or mirror, the greater the light-gathering capability of the telescope. Optical telescopes have been used for 400 years beginning with Dutch lens-grinding technology and Galileo’s first telescope observations in the 1600s.

Types of Optical Telescopes refracting telescope - uses two lenses to gather and focus light disadvantage: the maximum lens size is about 1 m reflecting telescope - uses curved mirrors to gather and focus light advantage: can be segmented instead of being one single piece and can reach a size of 10 m e.g. Keck telescopes on Mauna Kea, Hawaii

Keck 1 and Keck 2 Mauna Kea, Hawaii Fragment G Fireball A Keck telescope image of Comet Shoemaker-Levy hitting Jupiter in 1994. Keck 1 and Keck 2 Mauna Kea, Hawaii

The next series of Solar System photos were taken by an amateur astronomer using an 8-inch reflecting telescope. Sun

Moon

Mercury Venus

Mars Jupiter

Saturn Pluto

Interferometry Telescopes can be linked together for greater magnification and resolution. The combined telescopes are spaced separately but have their images combined digitally using computers. magnification = making an object appear larger resolution = the ability to distinguish two points as different

The Hubble Space Telescope The Hubble telescope is a reflecting telescope orbiting Earth at an altitude of 600 km. For a long time it was the best “Earth-based” method of reducing interference from moisture, clouds, wind, air and light pollution. Spiral Galaxy M100 M100 is so distant that this image shows its appearance at the time of the dinosaurs.

The Hubble Space Telescope is a cooperative program of the European Space Agency (ESA) and NASA to operate a long-lived space- based observatory for the benefit of the international astronomical community. HST was envisioned in the ‘40s, designed and built in the ‘70s and ‘80s, and operational in the ‘90s. HST was designed to be a long term space-based observatory.

The Hubble Space Telescope To accomplish this and protect the spacecraft from instrument and equipment failure, regular servicing missions occur. Hubble has special grapple fixtures, 76 handholds, and is stabilized in all three axes. HST is a 2.4-meter reflecting telescope and was deployed by the space shuttle Discovery in 1990.

(Hubble Space Telescope) Neptune (Hubble Space Telescope) http://www.youtube.com/watch?v=--X9zfgZtS0 Uranus (Hubble Space Telescope)

The New Space Telescope James Webb Space Telescope is set to launch in 2018! 18 large mirrors that will collect infrared light, sheltered behind a tennis-court-size sun shield. http://www.space.com/34593-james-webb-space-telescope-complete-2018-launch.html#ooid=d1NmE3NzE6WDhuFROPfaH-6xrA0EhC6W https://jwst.nasa.gov/about.html

3.2 Seeing Beyond the Visible Current technology does not rely on the visible spectrum of light alone to explore the universe. Many objects also radiate invisible forms of electromagnetic energy at the speed of light. Examples are X-rays, radio waves, microwaves, infrared, ultraviolet and gamma rays. Each type of wave has a distinctive wavelength and frequency. wavelength - the distance from one point of a wave to the next point (e.g. crest to crest)

frequency - number of waves passing a point per second What are the advantages in using other parts of the electromagnetic spectrum to study the sky instead of relying on light? 1) Radio waves can pass easily through most surfaces 2) Not affected by weather 3) Detected day or night 4) Not blocked by clouds or atmosphere and pollution 5) Can travel farther then light 6) Harmless form of energy to humans.

Combining the power of the Hubble Space Telescope with the Chandra X-ray Observatory, researchers have made images of a rotating star that provides new clues about how the powerful object works.

Scientists gathered data at different times over several months with the two orbiting observatories, examining the so-called Crab Nebula and its dense, pulsing neutron star. The rapidly spinning star generates incredible pulses of magnetic energy that scientists still struggle to understand.

Crab Nebula Pulsar A composite image of the Crab Nebula shows the X-ray (blue) and optical (red) images superimposed. The Crab was first observed by Chinese astronomers in 1054 A.D. and has since become one of the most studied objects in the sky.

Radio Telescopes Radio telescopes are basically satellite dishes made of metal mesh. The dish is a large antenna that gathers and focuses radio waves onto the middle receiver where they are converted to electrical impulses then sorted out by a computer. https://www.youtube.com/watch?v=mL-BYWkY6m0

Interferometry, or using arrays, can be used to simulate a much larger telescope. Ex. Two small radio telescopes 100m apart mimic the ability of one single radio telescope with a dish diameter of 100m!

The Very Large Array consists of 27 radio antennas in a Y-shaped configuration on the Plains of San Agustin, New Mexico. Each antenna is 25 m in diameter. The data from the antennas is combined electronically to give the resolution of an antenna 36 km across, with the sensitivity of a dish 130 m in diameter.

Black holes are objects with such high gravity that not even light can escape. They may be formed when the most massive of stars die and their cores collapse into a super-dense mass. A black hole radio telescope image by the Very Large Array.

The bottom image is the quiet chromosphere of the Sun taken with the Yohkoh soft X- ray telescope. The concentric circles superimposed on the image indicate the location and field of view of two VLA images made in 1992.

Space Probes Optical and radio telescopes can find out much about the structure of matter in the universe. But one thing they can not do is conduct tests on soil, for example, on Mars. Accurate knowledge about the soil is needed in planning the first manned mission to Mars. Space probes and robot explorers, though extremely expensive, provide this information without risk to human life.

3.3 Interpreting Space What Are Stars Made Of? Astronomers use the visible spectrum of light to study the composition of stars from here on Earth. Each star emits a fingerprint of black lines where its elements absorb light. The resulting spectrum looks like a rainbow with black vertical lines on it. SUN

The instrument used to analyze a star’s spectrum is called a spectrometer. The other data needed is a list of known spectra for elements in the Periodic Table. A spectroscope helps us find out what stars are made of. It disperses, or separates, white light from a star into a very wide spectrum of colors — much wider than a normal prism does. When spread very wide, black lines appear in the spectrum. Spectrometer

The first scientists to observe these lines wondered why they were there and what they meant. It turns out that particular elements in the star created particular patterns of lines. Once scientists knew the element responsible for a certain pattern, they knew which elements were present in the star. This was a revolutionary discovery.

This hydrogen emission spectrum was produced by exciting a glass tube of hydrogen gas with about 5000 Volts from a transformer.

Star Direction of Motion Scientists can determine if a star is moving toward or away from us by looking for a blue-shift or red-shift in the light that reaches Earth. The principle involved is the Doppler effect. http://www.youtube.com/watch?v=Tn35SB1_NYI http://www.youtube.com/watch?v=4cCk1MXJHm0 The pitch (tone) of a sound wave changes depending on whether the object is moving toward or away from the observer. Light is also made of waves, so light can also change depending on whether it is moving toward or away from the observer.

ex. an ambulance siren’s pitch is higher as it approaches the observer and falls as it passes by. This is because the waves in front are compressed and in back are stretched out. Compressed waves are high pitch, stretched waves are low pitch.

A star moving toward Earth will have its waves compressed (short light waves are blue). This is called a blue shift. A star moving away will have its waves stretched (long light waves are red). This is called a red shift

http://www.youtube.com/watch?v=jw8VYKGQk-I The red and blue shift caused by a star's 'wobble' as it is tugged back and forth by its planetary companions.

Measuring Distance Mathematics and physics are powerful tools in helping to measure distances in space. Two methods for calculating distance include: 1) triangulation 2) parallax Triangulation is based on geometry while parallax uses the apparent shift of an object compared to its background when viewed from two different angles.

Parallax Parallax is the apparent shift of a nearby object compared to more distant background objects. It occurs when the target object is viewed from two different angles. These two different views are then used in triangulation calculations. The largest baseline on Earth is the diameter of Earth’s orbit around the Sun. summer winter How long apart would measurements be taken?

How long apart would measurements be taken? 6 months apart!!! 1AU = 150,000,000 km (approximately!)

Triangulation 1) Locate the object whose distance is to be measured. 2) Measure a baseline. The longer, the better. 3) From the ends of the baseline, measure the angles “a” and “b” to the target object. 4) Draw a scale diagram. 5) Draw a perpendicular line. 6) Measure the perpendicular line. 7) Convert to real distance. a b baseline