this page is intentionally blank. a new view of the universe iii fred watson april 2005 a new view...

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A new view of the Universe III

Fred Watson

April 2005

A new view of the Universe III

Fred Watson

April 2005

What is a transit?What is a transit?

Transit geometryTransit geometryWhy isn’t there a Venus transit every year or so?

Venus’ orbit is tilted relative to Earth’s…

This makes transits of Venus

jolly rare events…

Cyclic phenomenon… Cyclic phenomenon…

Transits of Venus follow a 243-year repeating pattern.

They always occur in June or December

because that is when the Earth crosses the

line of nodes.

The dawn of the telescope era…

Della Porta’s sketch of 1609 shows the

principle. But it was Galileo

who turned it into an engine of discovery

in the same year

By the way, while we’re talking about the birth of the telescope…

To be published in the US September

by Da Capo

Put it on your Christmas list

TODAY!

The 1639 transitThe 1639 transit

Predicted by Jeremiah Horrocks (1618-1641). Observed by him at Much Hoole, 4 Dec. 1639.Had to dash off to church before the event started.Venus was in mid-transit when he returned.

Drat!I’ve missed the good

bit.

What he actually said…What he actually said…

‘Then I beheld a most agreeable

spectacle… a spot of unusual

magnitude and of a perfectly

circular shape…’

The 1639 transitThe 1639 transit

It was also observed by his friend William Crabtree (1610-1644), a Manchester cloth-merchant.

More transit geometryMore transit geometryWhy is a Venus transit potentially so useful?

It allows you to measure the distance to the Sun

Bright idea courtesy of Edmond Halley (1656-1742)

The 1769 transitThe 1769 transit

By then, telescopes had improved significantly.

And governments were prepared to fund expeditions to far-flung places to get the best view of the transit.

James Cook in Tahiti(And the rest is history…)

The 1769 transitThe 1769 transit

1874

The trouble with transitsThe trouble with transitsCook and others found their timings spoiled by the black-drop effect...

The 1874 transit in AustraliaThe 1874 transit in AustraliaHenry C. Russell:‘Never perhaps in the world’s history did morning dawn on so many waiting astronomers as it did on 9 Dec. 1874.’He observed from Sydney, Woodford, Eden and Goulburn.

Russell’s rival, John Tebbutt, disparagingly described his report on the 1874 transit as a ‘…gorgeous volume…’

And again in 1882…And again in 1882…

German transit expedition in Chile, 1882

Consternation!Consternation!

Photographic assistancePhotographic assistanceTaken by William

Harkness of the US Naval

Observatory, 6 Dec 1882.

(It was cloudy in Sydney.)

‘We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth, and the June flowers are blooming in 2004…

What will be the state of science when the next transit season arrives, God only knows.’

(Dec 1882.)

Harkness looks to the future…Harkness looks to the future…

The transit of June 2012…The transit of June 2012…

Don’t look directly at the Sun (especially not

through binoculars or a telescope)!

Use eyepiece projection (like Horrocks)

Or check webcasts from NASA and other

agencies (unlike Horrocks).

But what actually is a planet…?But what actually is a planet…?

Isn’t it obvious?

It’s one of these…

Or these…

Or maybe one of these…

In fact, it’s a seriouscontemporary problem.

Is it a star…?

What about ultra-low mass stars? Brown dwarf ~40 Jupiters

An object that shines only by reflected light?

To detect Jupiter need 12.5 m/s accuracy.For Saturn 2.7 m/s.

Attainable accuracy 2 m/s.

An object that orbits the Sun…?

An object that orbits the Sun…?

Gliese 876

An object that orbits a star…?

Free-floating objects in Orion with masses less than 13 Jupiters

951 Gaspra

An object big enough for its own gravity to crush it into a spherical shape?

And what about Pluto compared with Kuiper belt objects?

How are planets distinct from moons, asteroids, brown dwarfs, stars?Response of the International Astronomical Union (the only body that can make the definition) is:

‘Well, er…’Or, to be more precise:1) Objects orbiting around solar-type stars with true masses above the limiting mass for thermonuclear fusion of deuterium (currently calculated to be 13 Jupiter masses for objects of solar metallicity) are "brown dwarfs" (no matter how they formed) while objects with true masses below this limiting mass are "planets". 2) Free-floating objects in young star clusters (which presumably formed in the same manner as stars and have not been shown to be ejected from planetary systems) with masses below the limiting mass for thermonuclear fusion of deuterium are not "planets", but are "sub-brown dwarfs" (or whatever name is most appropriate).

The astronomical community wrestles with the definition of a planet…

What is the use of transits today?

So, looking for the characteristic dimming is a good way to find extra-solar planets…

And it might tell us much about the the planet and star, as well as how many are out there…

…such as the 0.9-m RCT (Robotically

Controlled Telescope) at Kitt Peak in

Arizona.

Hence new telescopes…Hence new telescopes…

Jeremiah Horrocks would have thought

this was a pretty neat way to see

planetary transits...

Jeremiah Horrocks would have thought

this was a pretty neat way to see

planetary transits...