Download The 2016 Transit of Mercury

The 2016 Transit of Mercury
And how to observe it
Dr Adrian Jannetta MIMA CMath FRAS
The 2016 Transit of Mercury
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Adrian Jannetta
T HE P LANETS
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O RBITS OF THE INNER PLANETS
Mercury and Venus can pass
between the Earth and Sun
(inferior conjunction).
The planet passes from the
evening to the morning sky.
Every 116 days for Mercury.
Every 584 days for Venus.
Transits are rare — the alignment
is rarely exact.
Why?
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M ERCURY T RANSIT C ONDITIONS
Inferior conjunction must occur close to a node of Mercurys orbit for a transit
to be visible. Transits are rare: just 14 between 2000 and 2100.
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V ENUS T RANSIT C ONDITIONS
Inferior conjunction must occur close to a node of Venus’s orbit for a transit
to be visible. Transits occur in pairs separated by 8 years, with 105 years or
122 years between successive pairs.
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P REDICTING TRANSITS
Kepler studied the planets and
derived three laws of planetary
motion (1609 — 1619).
Compiled the Rudolphine Tables
(1627) contained a star catalogue
and showed how to calculate the
positions of the planets
Keplers scientific ideas were not
widely accepted in his lifetime.
However, his methods predicted
transits of Mercury and Venus in
1631.
If the transits could be observed
— it would be strong support for
Kepler’s Laws.
Johannes Kepler (1571 — 1630).
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M ERCURY TRANSIT (1631)
Mercury transit was predicted for
November 7th 1631.
The transit was successfully
observed by Pierre Gassendi.
Venus transit was predicted to
happen in December 1631.
Gassendi watched and waited for it
— but it wasn’t seen.
The Venus transit actually occurred
but during night-time in Europe.
Pierre Gassendi (1592 — 1655).
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V ENUS TRANSIT (1639)
William Crabtree (1610 — 1644) observing the Venus transit in 1639.
Keplers data had predicted a near miss for Venus in 1639.
English astronomers Jeremiah Horrocks and his friend William Crabtree refined
the calculations; a transit would occur in 1639.
Horrocks (in Much Hoole, Lancashire) and Crabtree (in Broughton, near
Manchester) observed the start of the transit at sunset.
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Horrocks’ observations of the transit allowed him to estimate the Sun-Earth distance;
his figure of 60 million miles was 7 times bigger than astronomers had previously
supposed.
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K EPLER ’ S T HIRD L AW
Kepler’s third law of planetary motion (the Harmonic Law) describes
a relationship between the orbital period of the planet and its
distance from the Sun.
T2 ∝ D3
where T is the orbital period (in years) and D is the planet distance
from the Sun (in terms of the Earth-Sun distance).
By measuring the period astronomers could calculate the distance —
relative to our distance from Sun.
But astronomers had no direct way of measuring the Earth-Sun
distance. Transits of Mercury and Venus could potentially give the
answer.
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T HE SIZE OF THE SOLAR SYSTEM
In 1716 Edmund Halley (1656 — 1742) came up with a method to calculate the
Sun-Earth distance using transit timings.
Venus (or Mercury) follows a different path across the Sun seen from from widely
spaced latitudes on Earth. Transit timings would allow the calculation of the actual
distance. Venus, being much closer to Earth, is easier to measure.
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V ENUS TRANSITS (1761 AND 1769)
Many expeditions to far flung
locations to record timings for these
transits.
Astronomers were granted safe
passage in 1761 despite the Seven
Years War between England and
France.
Captain James Cook led an
expedition to Tahiti in 1769.
Hundreds of measurements were
made.
James Cook (1728 — 1779).
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T RANSIT OBSERVATIONS (1769)
Timings from the Venus
transits badly affected by a
so-called black drop effect.
However, data from both
transits gave an Earth-Sun
distance of 153 million km
(with an uncertainty of ś1
million km).
The absolute size of the
solar system — distance to
the Sun and planets in
miles (or km) become
known.
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T HE B LACK D ROP E FFECT
Venus and Mercury both
show this effect
Therefore, not caused by the
atmosphere of the transiting
planet.
Bad seeing conditions in our
atmosphere? Blurring of a
high contrast image?
Diffraction effects in the
telescope?
Black drop not widely
observed with the 2004
transit of Venus.
Satellite images show this
effect for transits of Mercury.
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T HE ATMOSPHERE OF V ENUS
During the 1761 transit Mikhail Lomonosov (1711 — 1765) observed a ring of light
around the planet Venus which he attributed to sunlight being refracted through the
Venusian atmosphere.
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V ENUS TRANSITS (1874 AND 1882)
Sun-Earth distance refined
to 149.6 million km (Simon
Newcomb) using data
from all previous transits.
First photographs of a
Venus transit.
Parallax measurements
were superseded by more
accurate methods (radar
reflection, Mars parallax).
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V ENUS TRANSITS (2004 AND 2012)
New focus: refine
techniques for finding
planets around sun-like
stars.
Most widely observed
transit to date! VT-2004
project had nearly 3,000
participants around the
world. Many school
children made timings of
transit.
The AU measured to
within a fraction of the
accepted value.
No more Venus transits
until 22nd century...
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O BSERVING THE M ERCURY TRANSIT
It is dangerous to look at
the Sun.
Mercury is very
small...optical aid
essential.
Binoculars and telescopes
must be properly filtered.
Homemade filters: take
care constructing and
securing housings for the
filter.
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T RANSIT TIMES FOR 09-M AY-2016
Transit times will vary with
latitude. The following times
are accurate for
Northumberland:
First contact: 12.12pm
Second contact: 12:15
Mid transit: 3:57pm
Third contact: 7:37pm
Fourth contact: 7:40pm
These timings are local (BST).
Observing safely (but without dignity).
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W ILL IT BE SUNNY ?
Maybe...!
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F UTURE TRANSITS
Some future transits of Mercury...
Date
Visible from UK?
2016 May 09
2019 Nov 11
2032 Nov 13
2039 Nov 07
Yes.
Partly; transit begins before sunset.
Partly; transit in progress at sunrise.
Partly; transit in progress at sunrise.
Some future transits of Venus...
Date
Visible from UK?
2117 Dec 11
2125 Dec 08
2247 Jun 11
2255 Jun 09
No.
Partly; transit in progress at sunrise.
Yes.
Partly; transit in progress at sunrise.
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E ARTH TRANSITS ( FROM M ARS )
Transit of the Earth (and moon) as seen from Mars! This will happen on 10-Nov-2084.
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The End
Thank you :-)
Dr Adrian Jannetta MIMA CMath FRAS