Xi Zhang E&MS A261 <xiz@ucsc.edu> Planetary Discovery in the era of Spacecraft Exploration Xi Zhang E&MS A261 <xiz@ucsc.edu> TA: Szilard Gyalay <sgyalay@ucsc.edu>

Lecture notes will be posted before and after each lecture. Course Website: http://es.ucsc.edu/~xiz/file/EART8 Lecture notes will be posted before and after each lecture. Xi’s Office Hours: Monday/Friday, 4:00-5:00 p.m. or by appt. Discussion Sections (Mandatory, E&MS D258): (1) Tuesday, 6:00-7:00 p.m. (2) Thursday, 2:00-3:00 p.m.

Outline of this week Homework #3 is online Telescope Spacecraft Space Exploration and Spacecraft

Today’s Outline Review of spectra Telescope

Properties of Thermal Radiation Hotter objects emit more light at all frequencies per unit area. Hotter objects emit photons with a higher average energy. The hottest stars are the blue stars. Larger objects can emit more total light even if they are cooler. Remind students that the intensity is per area; larger objects can emit more total light even if they are cooler.

Energy Levels of Atoms Each type of atom has a unique set of energy levels. Each transition corresponds to a unique photon energy, frequency, and wavelength. Chemical Fingerprints

Chemical Fingerprints Downward transitions produce a unique pattern of emission lines. Those atoms can absorb photons with those same energies. Upward transitions produce a pattern of absorption lines at the same wavelengths.

Energy Levels of Molecules Molecules have additional energy levels because they can vibrate and rotate.

The large numbers of vibrational and rotational energy levels can make the spectra of molecules very complicated. Many of these molecular transitions are in the infrared part of the spectrum.

What are the three basic type of spectra? Continuous spectrum, emission line spectrum, absorption line spectrum How does light tell us what things are made of? Each atom/molecule has a unique fingerprint. We can determine which atoms/molecules something is made of by looking for their fingerprints in the spectrum.

How does light tell us the speed of a distant object? Doppler Effect The amount of blueshift or redshift tells us an object's speed toward or away from us. This figure from the book can give an introduction to the Doppler effect.

Measuring the Shift Stationary Moving away Away faster Moving toward Toward faster We generally measure the Doppler effect from shifts in the wavelengths of spectral lines.

Universe is expanding: Redshift Observed by Edwin Hubble (1929) Edwin Powell Hubble (1889 –1953)

From Eyes to Telescopes

Refraction and Light Focusing Refraction is the bending of light when it passes from one substance into another. Your eye uses refraction to focus light. Refraction can cause parallel light rays to converge to a focus.

Image Formation The focal plane is where light from different directions comes into focus. The image behind a single (convex) lens is actually upside-down!

Recording Images Digital cameras detect light with charge-coupled devices (CCDs). A camera focuses light like an eye and captures the image with a detector. The CCD detectors in digital cameras are similar to those used in modern telescopes.

Image Processing Astronomers often use computer software to combine, sharpen, or refine images. This image of Saturn's moon Enceladus has been processed to highlight the plume of water ice coming from its surface.

The two most important properties of a telescope 1. Light-collecting area: Telescopes with a larger collecting area can gather a greater amount of light in a shorter time. Depends on telescope's diameter. 2. Angular resolution: Telescopes that are larger are capable of taking images with greater detail.

Light-Collecting Area A telescope's diameter (d) tells us its light-collecting area (A): The largest telescopes currently in use have a diameter of about 10 meters. Twin Keck telescopes on Mauna Kea in Hawaii

Angular Resolution The minimum angular separation that the telescope can distinguish. Larger telescopes are capable of greater resolution because there's less interference.

Angular Resolution The rings in this image of a star come from interference of light wave. This limit on angular resolution is known as the diffraction limit, which is proportional to the wavelength of the light (λ) divided by the diameter of the telescope (d): λ/d Close-up of a star from the Hubble Space Telescope

Two basic designs of telescopes Refracting telescope: focuses light with lenses Reflecting telescope: focuses light with mirrors

Refracting Telescope Refracting telescopes need to be very long, with large, heavy lenses.

Reflecting Telescope Reflecting telescopes can have much greater diameters. Most modern telescopes are reflectors.

Mirrors in Reflecting Telescopes Pick-up images. Point students' attention to the human in the middle of the Keck mirror! Twin Keck telescopes on Mauna Kea in Hawaii Segmented 10-meter mirror of a Keck telescope

Primary mirror of James Webb Space Telescope

Three Primary Observing Methods Imaging: taking pictures of the sky Spectroscopy: breaking light into spectra Time Monitoring: measuring how light output varies with time

Imaging Astronomical detectors generally record only one color of light at a time. Several images must be combined to make full-color pictures.

Imaging Astronomical detectors can record forms of light our eyes can't see. Color is sometimes used to represent different energies of non-visible light.

Spectroscopy A spectrograph separates the different wavelengths of light before they hit the detector.

Spectroscopy Graphing relative brightness of light at each wavelength shows the details in a spectrum.

Time Monitoring A light curve represents a series of brightness measurements made over a period of time.

What are the two most important properties of a telescope? Collecting area determines how much light a telescope can gather. Angular resolution is the minimum angular separation a telescope can distinguish. What are the two basic designs of telescopes? Refracting telescopes focus light with lenses. Reflecting telescopes focus light with mirrors. The vast majority of professional telescopes are reflectors. What are the three basic observing methods? Imaging Spectroscopy Time Monitoring