Showing posts with label Mercury. Show all posts
Showing posts with label Mercury. Show all posts

November 24 - First Observation of a Transit of Venus

  Posted on November 24, 2021


This is an update of my post published on November 24, 2010:



Every once in a while, one of the planets gets between us and the Sun. These planets are too far away to cast a shadow on our planet or to block much of the sunlight—in other words, they don't eclipse the Sun like the Moon occasionally does. Instead, from our point of view, they appear as tiny black dots that travel across the disc of the Sun. This is called a transit.

Only two planets can be seen in transit across the Sun from the Earth. Do you know which ones they are?

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ANSWER: Mercury and Venus are both closer to the Sun than we are here on Earth, so they are the only planets that can get between us and the Sun.



Anyway, Jeremiah Horrocks was an English astronomer. He was the only person known to have predicted the transit of Venus on this date in 1639, and he is one of only two to have observed and recorded it. (His friend William Crabtree was the other.)

You may be wondering how he—or anybody—could watch a transit across the blindingly bright Sun. Well, he focused the image of the Sun through a simple telescope onto a piece of cardboard. He then watched the not-so-bright image on the cardboard. People still make this simple kind of helioscope these days, although astronomers have of course figured out more sophisticated systems with which they study the Sun.

NOTE: Never look at the image of the Sun EVEN with a helioscope without adult supervision.


A Rare Treat!

Transits of Venus are very rare. They happen in pairs that are eight years apart—and these pairs are separated by around 100 years! The last two transits of Venus occurred in 2004 and 2012. For many of us, that will likely be the last of our lifetimes! The next transit will be in December, 2117.

Transits of Mercury are much more frequent. The last one was in 2019, and the next one will be in 2032.


Notice how much larger Venus's dark disk looks
against the brightness of the Sun (above),
compared to Mercury's teeny spot (below),












Tie One On Day in the U.S.

(Day before Thanksgiving in the U.S.)






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October 24 - Recycle Your Mercury Thermostat Day

Posted October 24, 2019

Quicksilver!

The name is pretty romantic, and you can see from this video (around the 1:44 mark) why the element mercury used to be called this.

A lot less romantic label for mercury is neurotoxin! It's a really, really dangerous heavy metal that poisons brains and nerves!

That's why it is so so so so so important not to throw things with mercury in them into the trash! Instead, old thermometers, thermostats, and lightbulbs should be carefully recycled. In my community, I would take these items to my local hazardous household waste disposal site. For more possibilities for proper recycling or disposal, check this website.





Mercury is just a very odd element - the only metal that is liquid at room temperature! It's such a dense liquid, many metal objects can float in mercury. Small amounts of mercury on a surface form balls (larger amounts flatten out because of gravity), and liquid mercury doesn't get anything that touches it wet.

To see all of these weird characteristics and to learn more about mercury, check out the videos of mercury put up by Taofledermaus, like this one. 






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March 29 – Anniversary of the First Mercury Fly-by

Posted on March 29, 2016

Mercury is one of the four rocky inner planets (and the smallest one - that's it on the far right), so it seems it would be fairly easy to send robotic space probes to this planet. But Mercury is so close to the Sun, it was tricky for the NASA scientists and engineers to design Mariner 10 to be tough enough to endure that environment.

The fact that Mercury is so close to the Sun
makes it difficult for us to see it in our skies.

It tends to be lost -- or almost lost -- in the
Sun's glow during dawns and sunsets.
Even though the Sun is the ultimate resource necessary for all of Earth's life – giving the light and heat that we need – being close to the Sun means getting a whole lot of radiation, including way too much heat as well as punishing doses of high-energy radiation.

So the Mariner needed shielding. It needed thermal blankets and sunshades. The sunshade scientists devised ended up being aluminized Kapton and glass-fiber sheets covered with Teflon! The solar panels, of course, could not be covered – their whole purpose was to soak up the sun's light so that they could make energy that the space probe needed – but solar panels do not work if they get too hot. So scientists created a way to tilt the solar panels so that the right temperature was maintained. Finally, the hydrazine rocket nozzle had to face the Sun in order to work; the exposed parts of the rocket nozzle were painted with special paint to reduce the heat flow to the rest of the probe.

Mariner 10 was launched on November 3, 1973, and it did its first fly-by on this date in 1974.

Mariner 10 ended up flying past Mercury three times. It mapped between 40% and 45% of the planet's surface by taking 2,800 photos. It discovered that Mercury has an extremely thin and unstable atmosphere made up mostly of helium, and it discovered that the planet has a magnetic field, which shows that it has a large iron-rich core.

This is one of the Mariner 10 photos
of Mercury.
The radiometer readings reveal that Mercury has nighttime temperatures of – 183 degrees Celsius ( -297 degrees Fahrenheit) and maximum daytime temperatures of 187 degrees Celsius (369 degrees Fahrenheit). So that's way more than twice as cold AND twice as hot as Earth.

Mercury endures the greatest temperature
extremes of any planet in the Solar System.
You may think to yourself, okay, I get the twice as hot part, since Mercury is so much closer to the Sun. But why are the nights more than twice as cold as Earth?

The answer is that it is Earth's atmosphere that keeps us relatively warm at night, compared to places with little or no atmosphere – like the Moon and Mercury. In those places, the heat from the rocks radiates away quite quickly, and then the cold of space is all that is left...



Also on this date:




































Plan ahead:
And here are my Pinterest boards for:


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