National Radio Astronomy ObservatoryGreen Bank, WV

Measuring the Size and Age of the Universe

You are an astronomer who has just made this image of the sky.

As you study this image, what questions do you ask?

What are these “fuzzy” objects?

Are they moving?

Are they part of a system? How far away are they?

What are they made of? How were they formed?

Neon

Sodium

Hydrogen

Radio Spectral Line

Hydrogen

NGC 628

Doppler Shifts

The Expanding Universe

If we assume:

•All spiral galaxies are similar in size to the Milky Way.

•Spiral galaxies are 10 kpc in radius.

Then we can estimate the distance to these galaxies.

TAN angle = Opposite Adjacent

R

Angular size

Distance

Distance = Radius

TAN angle

= Radius Distance

half angle in degrees tan Distance(kpc) distance(lightyear) Velocity(km/s)1.5 0.025 0.000436 22918.31035 74690773 2100

2 0.033333333 0.000582 17188.73191 56018077 15902.5 0.041666667 0.000727 13750.98466 44814459 1350

4 0.066666667 0.001164 8594.363048 28009029 680

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Distance (lightyears)

V (km/s)

Hubble Constant

1/T = H1/H =

Time!!!

Slope = V/D

T=

1x

D

D0

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Distance (lightyears)

V (km/s)

distance(lightyear) Distance (km) Velocity(km/s) H=V/D (km/s/km T (years)74690773 7.10468E+20 2100 2.9558E-18 1118776173056018077 5.32851E+20 1590 2.98395E-18 1108221626144814459 4.26281E+20 1350 3.16693E-18 1044190977028009029 2.66425E+20 680 2.55231E-18 12956410213

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Distance (lightyears)

V (km/s)

So, What is the Age of the Universe?

About 11 BY

August, 1999

October, 1999

Distance LadderDistance Ladder