Partial Lunar eclipse and Transit of Venus

[Dolphin]

TheTransit of Venus is ONE week away (Wednesday June 6).

There is also a partial Lunar eclipse on Monday June 4. Although
slightly less than 40% of the Moon being covered by Earths shadow it
will still be nice to watch. The eclipse starts at the family
friendly 7:59 pm AEDST (5:59 AWST), and mid eclipse is 9:03 pm AEDST
(7:03 pm AWST).

Also, if you are outside a bit earlier and in the sydney or outer suburbs of Sydney you may be able to see the International Space Station. It looks like a star moving slowly across the sky in the direction indicated, but there of course is no sound. It takes about 6 minutes to cross the sky. It is only visible when the sky is dark and the sun is shining on it. It disappears when it goes into the earth's shadow.


Keep looking up!

[Miker]

Well done Greg! I have a Moon Phases App on the iPad which is brilliant to check now and then.

I'll be out having a look!

[Phillip]

Geee, I hope the weathers OK!

[Dolphin]

Well actuallythe weather is not ok.
There is a solar storm that is about to hit the earth at 2100 tonight. It may cause aurora, but we wont see it. Take your Umbrella with you. Check your GPS!

[Dolphin]

With all the interest in the transit of venus, and the sun, here is a good site about the Sun and space weather. I watch it a lot.
And you thought the sun only came up and went down every day?

http://spaceweather.com/

Why was everyone so interested in the transit of Venus? Why was Cook sent to Tahiti to observe the transit at great expense to the Navy?

Look Up

[storm petrel]

Both were spectacular events and I enjoyed both before I went OS. As a physicist and as James Cook's greatx6 nephew, watching the transit for the second (and last) time in my life was a special experience. I am currently staying in a house just down the road from the small town of Waimea on the West coast of Kauai. It was at Wiamea, quite a rugged coastline, where Cook first landEd on the Sandwich Isles. The trades blow offshore here every day and I can see why Cook would have edged his Bark close to this shore.

Cheers,
Mark
Storm Petrel

[Miker]

Mark, hope your getting some waves. It's been pretty good here this week with the remains of the big low that came through.

[storm petrel]

It has only been 3-4ft, but that is fine here with warm water and powerful waves. Looks like the wind is going to remain constant NE and the swell remain this size from the SW for the next week at least. I love the names of the breaks here like, Acid drops and infinities.

Cheers
Mark

[Dolphin]

That's right Mark,
The transit of venus is much more important than just a spectacular event. In fact it was used as the method of calculating the size of the solar system.
Four expeditions were sent out by England and France. Cook's expedition was useful because it was located in the southern hemisphere. it was only shortly before Cook left that Tahiti was discovered and thought of high importance to the experiment. By observing the angle to Venus at various times during the transit and using basic trigonometery, along with the distances of the observing sites on the earth as a base line, it was possible to calculate the distance to Venus. It was then possible to extrapolate the distance to the Sun.
It was also the first time an atmosphere had been observed on another planet.
A French physicist calculated to better than 1% the Astronomical Unit (the distance to the sun) 153 odd million km.
After observing the transit of Venus, Cook opened sealed orders that required him to sail sout west and find the "Great Southern Land". It was thought that the amount of land in the northern hemisphere had to be balanced by the same amount of land in the Southern Hemisphere.
This was a great example of sailing and astronomy working together.
Some of this information was sourced from the ABC 1233 Newcastle.

[storm petrel]

Yes, Greg I am familiar with all of this. I have read many biographies of Cook and his diaries because of the family connection and I am also familiar with the AU and how viewing the transit enables an AU to be determined experimentally. Knowing the distance between the Sun and the Earth (AU = approx 150 million km) you can use the period of the Earth's orbit and Keppler's law of periods to calculate the distance to all the other known planets. When Newton later derived Kepler's Law by equating the expression for the gravitational attraction(he had proposed) between the sun and the earth with the centripetal force that must exist to keep the earth in its orbit he found the constant of proportionality between the cube of the period and the square of the average distance to the sun in Kepler's law of periods was 4 x pi squared, divided by the product of the mass of the central body and the universal constant of gravitation. So the transit also gave astronomers an accurate value for the mass of the sun as well as the distance between the sun and the earth. Newton used the moon/earth distance in a similar way together with the acceleration due to gravity on Earth to calculate the universal constant of gravitation and the mass of the earth initially, but that is another story. (I am not trying to be a smart ass here, I actually have first class honours and a PhD in physics and I have a genuine passion for all this stuff)

Cheers,
Mark