Lecture 12: Searching for planets orbiting other stars. I. Light & Telescopes

• Direct detection of planets around other stars.• Light and telescopes - optics.• Challenges and promises of direct detection.

Direct Detection of Planets

• Direct detection is challenging because of the technicallimits oftelescopicobservations

Light & Matter interact in 4 basic ways

The nature of light

• Light - electromagnetic waves that have:

Wavelength

Frequency

Speed

… and

Energy

The nature of visible light

• Obeys the inverse-square law:

Direct Detection of Planets

• Direct detection is challenging because of the technicallimits oftelescopicobservations

Direct Detection of Planets• The best case to-date of a planet-like system detected ininfrared light:

Light and Telescopes - Optics

• Optics - creating an image & collecting light:

Light and Telescopes - Optics

• Another function: Resolution

Light and Telescopes - Optics

•Resolution - theultimate limitationcomes from thewave properties oflight:

Light and Telescopes - Optics

• Resolution - theultimate limitationcomes from thewave properties oflight:

Light and Telescopes

• The challenge ofdetecting planets:

Spectrum of the Sun,and as it is reflected by3 of the planets:

Light and Telescopes

• Trying to ‘see’ theplanet in the strongglare of the star:

Telescopes - the Atmosphere

• Atmospheric ‘seeing’

Before After correction

Telescopes

• All large telescopesare reflectors:

Telescopes

• The largest today -the Keck telescopesare composite mirrorreflectors (D~ 10m):

They also form a pair -an interferometer.

Telescopes

• Harvard is a partnerin the constructionof the largest newtelescope:

The Giant Magellan Telescope (D ~ 25 m)

The Laser Astro-Comb

Main points to take home:

1) Visible light: form of electromagnetic energy (radiation) to which our eyes are sensitive.

2) Energy & power vs. color3) Four basic ways light and matter interact.4) Telescopes: optics & 2 types of design.5) Angular Resolution vs. light gathering