Astronomers Observe

Chris Stoughton

March 16, 2002

Observation• Direct or indirect?

• Unaided or with instruments?

• Accidental or planned?

• Immediate or long term?

• Funding!

First, a Tribute to William Herschel• 1738-1822

Discovery of Infrared Radiation

In the year 1800, Sir William Herschel “accidentally”discovered the existence of infrared radiation.NOTE: you need to blacken the bulb of the thermometer to get this to work.

Parallactic Shift

UranusIt had actually been seen many times before but ignored as simply another star.

The earliest recorded sighting was in 1690 when John Flamsteed cataloged it as 34 Tauri.

Herschel’s Milky Way

The Galaxy

The Milky Way in Different Wavelengths

Herschel -- an Observer• He made star counts, and found nebulae, etc.• He analyzed these counts to make a “picture” of the

Galaxy, as viewed from the outside – “indirect.”• He used an instrument, in fact, built his own.• A famous discovery was made by accident.• That got him funding!• His planned observations, which took 20 years, led to

a more profound result.

Annie Jump Cannon

Oh, Be A Fine Girl--Kiss Me!

This phrase has helped several generations of astronomers to learn the spectral classifications of stars.

At Work in Cambridge, MA

Stellar Spectra

Cecilia Payne-Gaposhkin

Annie and her Colleagues• Data Collection (direct observation) and Data

Analysis (indirect observation) both have to be accomplished.

• Pickering had the observational horsepower to do “fact accumulation” but he did not appreciate the value of theory.

• “Astrophysics” brings down-to-earth physical laws to the sky.

• The flood of “accidental” observations turn out to make sense only after classification.

• Funding provided by Anna Draper led to the “Henry Draper Memorial.”

• Interpreting results using “astrophysics” yields enormous payback!

The Big Bang• A long time ago, the Universe we live in was

incredibly small, dense and hot. Many different observations support this view and it now appears that the Universe underwent a very dramatic event right at the beginning, known as the Big Bang.

• Different estimates put the Big Bang some 13 to 17 thousand million (13 - 17 billion) years ago.

• Since then the Universe has expanded, cooled down and has become much less dense.

Observational Pillars • Expansion of the Universe • Origin of the cosmic background radiation • Nucleosynthesis of the light elements • Formation of galaxies and large-scale structure

• The Big Bang model makes accurate and scientifically testable hypotheses in each of these areas and the remarkable agreement with the observational data gives us considerable confidence in the model.

Expansion of the UniverseVelocity = H * distanceVelocity = H * distance

Cosmic Microwave Background

Big Bang Nucleosynthesis

Observational Cosmology• The observations we make are indirect – based on

compiling a large number of direct observations.• The types vary: recessional velocities, spectrum of

microwave “noise”, and the amount of Hydrogen, Helium, Deuterium, and Lithium.

• The instruments are a key here – developing instruments is an important, and at times neglected, endeavor.

• Slipher “accidentally” saw (but did not realize it) that the Universe is expanding, while looking for ET.

• Cosmological observations are planned, and long term.

• Is the funding worth it?

Industrial Astronomy -- SDSS

Cover ¼ of the sky

Images of 300 million objects

Spectra of 1 million objects

400 people; 12 institutions

Data Collection will continue until June, 2005The “early data release” is available at skyserver.sdss.org,Along with educational modulesPlease, if you want to help, use these, evaluate them, and let us know How to improve them!

SDSS Web Sites

• http://www.sdss.org/ -- general information

• http://www.sdss.org/gallery/gal_zqso.html -- how quasars change with redshift

• http://skyserver.fnal.gov – outreach and education

• Please critique and send your question, comments, complaints, praise, and bribes to me, Chris Stoughton, stoughto@fnal.gov