Physics 2051 Bio-Astronomy of Solar Systems Chapter 5 Questions 7-10 Astrobiology a Multidisciplinary Approach By Jonathan Lunine

7. Hubble Space Telescope vs. James Webb Space Telescope HST mirror aperture 2.5 meters JWST diameter 6.5 meters The optical limit, defined by the size of the telescope mirror, is called the diffraction limit. Larger apertures are required to see dimmer, more distant objects. More distant objects are farther back in time because the speed of light is finite.

HST vs. JWST Earth’s atmosphere contributes to a degradation in seeing because of turbulence. Space-based telescopes and adaptive optics are two ways to improve images.

Red-shift The dimmer the galaxy, the larger the distance from Earth, and the more the spectrum is shifted toward the red. Known as the Doppler effect, it works for light as well as sound waves. Edwin Hubble showed that space is expanding in all directions. Telescopes that can “see” in the infrared can see farther back in time.

The history of astronomy is the history of receding horizons The history of astronomy is the history of receding horizons. - Edwin Hubble Galaxy Cluster Lenses Farthest Known Galaxy http://antwrp.gsfc.nasa.gov/apod/ap040217.html

8. Hertzsprung-Russell Diagram An HR diagram plots luminosity vs. effective temperature. The Sun is a main sequence type G star. K and M stars are less massive than the Sun and burn longer. Less massive stars are less stable producing large flares.

HR Diagram The Earth’s magnetosphere protects life on Earth from high energy particles released by the Sun. The Earth’s core is a source of heat for the planet, beyond the solar radiation it receives.

HR Diagram + Longer burning stars allow longer time scales for life to evolve. - A planet orbiting a dimmer, cooler star would need to be closer to the star than the Earth is to the Sun in order to be warm enough to support life. - Flares from a K or M star would produce high energy particles and radiation that could be disruptive to life.

9. Intergalactic Dust (a) If we assume that all galaxies have the same brightness, and dust dims the light from a galaxy, then we might think the galaxy is farther away than it really is.

Intergalactic Dust (b) If we assume that red-shift is associated with expansion of the cosmos and galactic dust reddens light from a galaxy, we might think the galaxy is farther away and older than it really is.

Intergalactic Dust The most red-shifted galaxies posses a relativistic velocity approaching the speed of light!

10. Radio signals from an ancient civilization Radio signal sent at the frequency of microwave lines of water or hydrogen. Ancient civilization indicates base frequency in message. E = hc/λ = hv Planck’s constant, h Wavelength of light, λ Frequency of light, v Speed of light, c

Ancient Radio Signal Red-shifting would increase the wavelength of the signal received (and decrease the frequency). λ = c/v We can use this information to measure the distance traveled and the elapsed time.

Ancient radio signal Microwave radiation wavelengths are on the order of 10^-3 meters (mm). Radio waves can be 1 meter, 1 kilometer, or > 10^4 meters in wavelength. Microwave frequency at 1 gigahertz (10^11 Hz). Radio frequency at about 1 kilohertz (10^5 Hz).

Unwise Microwave Oven Experiments http://www.amasci.com/weird/microexp.html http://apache.airnet.com.au/~fastinfo/microwave/ball.html Using magnesium to generate a plasma inside a microwave oven.