Length of the SeasonsVenus Transit

June 8th, 2004

The UniverseDr. Scott SchneiderDr. Scott Schneider

Friday April 23rd, 2004

Presentation for National Astronomy Day (technically 04/24/04)

Webpage : http://www3.ltu.edu/~s_schneider/astro/astroday_2004.shtml

Lengths of the Seasons change

• Earth orbit is “drifting” around the Sun– Precession of orbit

• Caused by pull from planets and Moon

– Close/Far points in orbit move

• We adjust calendar with leap days– To prevent snow in July!

• But duration of seasons oscillate

How to find your way in the Solar system :

• All planets go around the Sun– also, in the same “direction”

• Define reference plane as Earth-Sun– Called the ECLIPTIC– All other planet orbits tilted, relatively

• Venus has an orbit tilt of about 30

– Save this info for later!

Seasons vs. Aphelion/Perihelion

• Spring defines quadrants

• Quadrants near Aphelion are longer in time

• Perihelion and Aphelion drift – so season lengths change

Season duration – short time scale• Currently Spring/Summer are longer

– But, Spring duration shrinking .. Fall rising!

Season duration – long time scale• Winter longest before –4000 (shortest ~3500)

Follow Spring Equinox Date (wide)• Spike around 1600? – Gregorian Reformation!

Follow Spring Equinox Date (med)• Small shifts at 100, none at 2000, 2400, 2800??

Follow Spring Equinox Date (zoom)• Slow drifting of the date later in March

More info on seasons?

http://www3.ltu.edu/~s_schneider/astro/seasons.shtml

(Unlinked to show the underscores …)http://www3.ltu.edu/~s_schneider/astro/seasons.shtml

What is a transit?• Planet crosses the face of the Sun• Mercury and Venus = closer to the Sun

– occasionally pass between Earth + Sun

• Transit of Earth for the Moon?– Lunar eclipse

• Transit of the Moon seen by the Earth?– Solar eclipse!

Features of Venus Transits• Nearly circular orbit

– Transits at each node in equal numbers

• Mercury : Less often in May than November– Moving faster in orbit in May

• Only seen from part of the Earth– Usually a whole hemisphere– Sometimes “grazing” – only part of hemisphere

• 243 year cycle (with 8 year and ~ 100 shifts)• Venus “large” enough to see “naked” eye

– Must use eclipse glasses or protected scope!

Rarity of Venus Transits?• Between –2000 and 4000 – only 81• No human alive has seen one (1882)• Transit of 1631 predicted by Kepler

– But not seen!

• Currently occurs in June or December– Usually occur in pairs – 8 years apart

• Because 13 revolutions of Venus ~ 8 of Earth

– Another period of ~105-110 years– Strong period of 243 years (forms “series”)

Historical notes of Transits• Mercury ~ 1/158 to 1/195 of Sun’s disk

– Not seen without a telescope!

• Venus ~ 1/31 to 1/32 of Sun’s disk– Visible w/o telescope (but with FILTER!)

• Venus transits widely observed in late 1700’s and 1800’s

Ecliptic plane - Today• Oriented by Seasons (Spring = pivot)• Venus orbit = Blue = above … Green = below (nodes)

SPRING

WINTER

FALL

SUMMER

Ecliptic plane – at Transit• Oriented by Seasons (Spring = pivot)• Venus orbit = Blue = above … Green = below (nodes)

SPRING

WINTER

FALL

SUMMER

Right place - Right time!• Venus makes more orbits than Earth

• Often passes those crossing points (nodes)– But, Earth isn’t always there to see it!

• One “face” of the Earth gets best view– Transit is at most ~ 8 hours

• Short time scale - not a good match– Wait many years, orbits match nicely!

What does “a pass” mean?

• Nov/Dec transits - lower left to upper right

• May/June transits upper left to lower right

• As the “cycle” advances, individual passes will move either “up” or “down” relative to the center of the sun

• A “series” would be a set of passes

How would a “series” look?

Full Series

“B”

243 Year period

What about a “pair”?

8 year jump between

consecutive series

Can I investigate the transits myself?

Sure! Here is the website for my very first home-grown Java applet – the

Venus Transit applet!

http://www3.ltu.edu/~s_schneider/astro/transits/venusjava.shtml

(Unlinked to show the underscores …)http://www3.ltu.edu/~s_schneider/astro/transits/venusjava.shtml

Tuesday, June 8th, 2004

• Circumstances for Detroit:• Sunrise 05:54 AM (Venus past midpoint of transit)

– Venus rises a few minutes later (tip of sun = “sunrise”)

• Venus touches inside edge of sun (on way out) = 7:05 AM at 11 degrees above the horizon

• Venus touches outside edge = 7:25 AM at 140 alt• Possible trip to Metro Beach MetroPark?

– (Better view of sunrise)

• Wear your glasses!!

Great prediction webpage : http://sunearth.gsfc.nasa.gov/eclipse/transit/TV2004.html

But can we really see it?

Luckily, we have a sunspot

today (04/23/04) – it

is a little smaller .. and we can see IT!

References

Jean Meeus – TRANSITS – Willmann-Bell

Jean Meeus is an Astronomer from Belgium – does some absolutely amazing astronomical calculations.

Has three other excellent books :

Astronomical Algorithms

Astronomy Morsels

More Astronomy Morsels

What about Marvin?

He wanted to blow up the Earth because it blocked his view of Venus!

Conditions for blocking ..

•How often does Earth block Venus?

•Calculate the location where the Venus-Mars line crosses the ecliptic – if the Earth is there also – block!

After the computer pulled a few all-nighters …

From the year 1000 to 3000 …

Only one time = Nov 8th, 2746 ~ 7:45 pm

Conclusion …

Marvin is just a big foo-foo head!!

Last but not least …The Universe!

• Logarithmic distance scale (y axis)– Need strong kung-fu math to squash the distance

scale of the Universe!

• “Hour angle” (right ascension) (x axis)– Measured from “Spring” event – (line in space)– 360 degrees = 24 hours

• The Universe on the Second Floor!• Much more info here :

– http://www.astro.princeton.edu/~mjuric/universe/

Astro Wall Volunteers

• James Mason *

• Clark Adamczyk *

• Steven R Moberly *

• George Swan *

• Lindsay Zaremski

• Adrian Brdarski

• Jeremy Dunaj

• Judy Sullivan (Custodian) – Cleaner of the Solar System!

* Members of LTU’s first undergraduate Astronomy course

These students helped me put little dots on the wall, and big giant strips of tape.

This talk, and other exciting things can be found …

http://www3.ltu.edu/~s_schneider/astro/index.htm

Thank you, Thank you,

Good Good Night, Night,

Drive Safely!Drive Safely!