Announcements:Announcements: Simple numerical error analysis Simple numerical error analysis

procedure on the websiteprocedure on the website Office hours changingOffice hours changing

Monday: 1:30-2:30Monday: 1:30-2:30 Wednesday: 1:30-2:30Wednesday: 1:30-2:30

Lab 2Lab 2

Lab 1 Grade DistributionLab 1 Grade Distribution Average (without zeros):71Average (without zeros):71 Average (with zeros):59Average (with zeros):59

TelescopesTelescopes We use telescopes to We use telescopes to

magnify distant magnify distant objectsobjects

There are two major There are two major types of telescopestypes of telescopes

Refractors – use lenses Refractors – use lenses Reflectors – use Reflectors – use

mirrors mirrors Many modern Many modern

telescopes are a telescopes are a hybrid of the twohybrid of the two

Our telescopes are Our telescopes are primarily reflectors, but primarily reflectors, but have a corrector plate have a corrector plate (big lens) on the front(big lens) on the front

MagnificationMagnification The magnification is determined The magnification is determined

by the focal lengths of the by the focal lengths of the telescope and eyepiece. telescope and eyepiece. (M=f(M=f

telescopetelescope/f/feyepieceeyepiece))

Focal length is the distance Focal length is the distance between the lens/mirror and where between the lens/mirror and where an object coming from infinity is an object coming from infinity is focusedfocused This is why many telescopes are This is why many telescopes are

longlong Reflectors advantageous here – Reflectors advantageous here –

can fit a longer focal length inside can fit a longer focal length inside a smaller regiona smaller region

Can you have too much magnification?Can you have too much magnification?

Too Much MagnificationToo Much Magnification Its tempting to zoom in as much as possible, but Its tempting to zoom in as much as possible, but

everything has limitseverything has limits More magnification makes image dimmerMore magnification makes image dimmer

Light spread over a larger areaLight spread over a larger area You not only magnify your target, but everything in You not only magnify your target, but everything in

between as well (atmosphere)between as well (atmosphere)

Brighter ImagesBrighter Images Most of what we look at Most of what we look at

through telescopes are far through telescopes are far away and dimaway and dim

We want to make our images We want to make our images bright!bright!

How do we get brighter How do we get brighter images images collect more light collect more light make telescope wider make telescope wider Refractors at a disadvantage – can Refractors at a disadvantage – can

only be so wideonly be so wide Some times this is not enoughSome times this is not enough

Many images are long Many images are long exposuresexposures

Hubble Ultra Deep Field (11 Hubble Ultra Deep Field (11 days-worth of light days-worth of light collecting!!!)collecting!!!)

Celestial Coordinate Celestial Coordinate SystemsSystems

Right Ascension and Right Ascension and Declination (RA/DEC)Declination (RA/DEC) Units?Units? Why is it advantageous Why is it advantageous

over other systems like over other systems like latitude and longitude?latitude and longitude?

And now tonight’s labAnd now tonight’s lab We’ll be measuring field of view of We’ll be measuring field of view of

our telescope (our telescope (angular size seen angular size seen through the telescope)through the telescope)

Primary Method – timing of stars Primary Method – timing of stars crossing the field of viewcrossing the field of view Can do this because the Earth Can do this because the Earth

rotates at a constant speed (15 rotates at a constant speed (15 degrees per hour)degrees per hour)

Time with a velocity gives a Time with a velocity gives a distancedistance

In case of cloudsIn case of clouds Can put the telescope into a rough Can put the telescope into a rough

alignment-->turns on the tracking alignment-->turns on the tracking motormotor

Look at a stationary object, moves Look at a stationary object, moves like a star in the sky-->mimics the like a star in the sky-->mimics the original processoriginal process

Procedural NotesProcedural Notes

Measure FOV crossing time at least 3 times Measure FOV crossing time at least 3 times and take an average.and take an average.

Don't forget to find theoretical field of view and Don't forget to find theoretical field of view and compare it to your measured field of view.compare it to your measured field of view.

You'll need a couple of specs for the telescope You'll need a couple of specs for the telescope and eyepiece – see the handoutand eyepiece – see the handout

Mind your units!Mind your units!• qq(degrees)=15(degrees/hour) x t(hours)(degrees)=15(degrees/hour) x t(hours)

• qq(arcminutes)=15(arcminutes/minute) x t(minutes)(arcminutes)=15(arcminutes/minute) x t(minutes)

• qq(arcseconds)=15(arcseconds/second) x t(seconds)(arcseconds)=15(arcseconds/second) x t(seconds)