Astronomy 1010 Planetary Astronomy Fall_2015 Day-21.

Astronomy 1010Fall_2015Day-21

Planetary Astronomy

Course Announcements• SW-chapter 6 posted: due Fri. Oct. 23

• Exam-2 will be returned on Friday

• 1st Quarter Observing night: Tuesday, Oct. 20; 7:30pm

Course Announcements• CHECK YOUR LAB GRADES IN D2L. If you are missing

grades, and have gotten the lab back, return it so we can enter the grade. (mostly Scientific Methods, but might be others as well.)

Telescopes & Instruments

The telescope is the astronomer’s most important tool.

Purpose: to gather light of all kinds.

Two kinds of optical telescopes: reflecting and refracting.

Invented in 1608 by Hans Lippershey.

Refractors use lenses to bend the light to a focus

Reflectors use mirrors to reflect the light to a focus

Catadioptric telescopes use both lenses and mirrors

Telescopes Telescopes have three functions:1. Gather light

LGP ∝ Area = πR22. Resolve objects

Θ = 2.06 X 105 (λ/D)

3. Magnify EXTENDED objects

The most important property of any telescope is to gather large amounts of light and concentrate it to a focus.

2radiusAreaPowerGatheringLight

Refraction is the bending of light when it goes from one medium to another

“n” is the index of refraction.

vcn

1 1 2 2sin sinn n

Refraction is governed by Snell’s Law:

Refracting telescopes use lenses.

Objective lens: refracts the light.

Aperture: size of the objective lens (larger aperture gathers more light).

The objective lens is placed in the aperture.

Since the eye already has a lens, the eyepiece is needed to bring the light rays back to parallel for the eye to see

Built in the late 1890’s, it is the last great refracting telescope.

This applies to camera lenses, your eye, telescopes and anything else that uses a lens to focus light

The compound lens takes two lenses of different materials and combines them to correct for color distortion

Since it is meant to be separated we don’t call it an aberration. Instead, it is called dispersion

Diffraction is much more efficient at separating light into its colors than dispersion

Look closely enough at stars and they aren’t just points of light but rings, too

i_Clicker QuestionTelescopes and Astronomical Instruments:

Refraction – Option 1

Lenses – Option 1

Reflecting telescopes use mirrors. There are primary and secondary mirrors. Focal length is determined by the path the

light takes reflecting off the mirrors.

Reflection is the bouncing of light off a surface

ri

Mirrors do not suffer from chromatic aberration and they do not cut off long or short wavelengths

Telescope mirrors are made so that the focus is a plane instead of a point

i_Clicker QuestionTelescopes and Astronomical Instruments:

Reflection – Option 1

Spherical Aberration

LSST Site – Artist Concept

LSST Site – 1st Blast – March 2011

Steward Observatory Mirror Lab

LSST M1 in polishing build-up

Coming “soon”The 30m Tele.