Sundials!

Above is an analemmatic sundial. The idea is to orient the sundial facing south, and then place a vertical pointer on the central figure-8 track, in a position corresponding to the date. The sundial above shows a simulated shadow for 2:15 PM yesterday. It can be seen that the sundial tells the time reasonably well, thanks to the inbuilt adjustment for variation in solar position.

For large-scale analemmatic sundials, like the one below, people can stand on the central figure-8 track and act as a human pointer. A sundial like this is fun to have in the garden.

Here are blank sundials for some Southern Hemisphere cities:

• Adelaide, Australia
• Brisbane, Australia
• Canberra, Australia
• Melbourne, Australia
• Sydney, Australia
• Johannesburg, South Africa

The ShadowsPro software will also generate sundials like these, if anyone is particularly enthusiastic.

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The Sun Again

This UV image from March 2012 (taken at 17.1 nm) shows a large solar flare (bright spot at upper left). It also gives a fantastic view of the solar surface generally. Thanks, NASA!

The analemma

If you photograph the sun at the same time every day (or every few days), you will find that the sun traces out a path in the sky, called the analemma. György Soponyai, in Budapest (Hungary), did exactly that at 8 AM each morning between 29 January last year and 6 January this year, to produce the wonderful photograph below (click to zoom):

More analemma photographs (by Anthony Ayiomamitis) can be found here. The shape of the analemma results from the fact that (1) the Earth is tilted on its axis by 23.5° and (2) the Earth orbits the sun in an ellipse, rather than a circle. The diagram below shows the calculated analemma for 12 noon at the Royal Observatory, Greenwich (latitude 51.48° N):

The concept of the analemma can also be used in constructing sundials. If an appropriate analemma is placed in the centre of the sundial, a gnomon placed at the right point on the analemma will correctly tell the time with its shadow (except for daylight-saving, of course).

Such sundials are popular in parks, because the viewer can stand on the analemma at a position corresponding to the current date, and his or her shadow will tell the time, without the need for additional time-of-year correction. I photographed the sundial above and below at Mt Stromlo Observatory in June 2012. It can be seen that the time was about 2:20 PM.

The loopy surface of the sun

The Solar Dynamics Observatory has taken this wonderful video of the activity going on at the hellishly hot surface of the sun – showing coronal loops, in particular.

See also these other SDO videos.

1957–58, the International Geophysical Year

The International Geophysical Year (actually a year and a half, from July 1957 to December 1958) saw the beginning of the “space race,” and the collection of a huge amount of valuable data. The science books I grew up with as a child were constantly referring to the results of the event.

The IGY, as it was abbreviated, included several solar eclipses (23 Oct 57, 19 Apr 58, 12 Oct 58) as well as the record-breaking solar maximum of 1957/58. In fact, February 11, 1958 turned out to be a very good night for Aurora chasers.

The IGY incorporated, among other activities:

• The Commonwealth Trans-Antarctic Expedition of 1955–58
• The 6^th Norwegian Antarctic Expedition of 1956–60
• The 3^rd Soviet Antarctic Expedition of 1957–59
• Operation Deep Freeze
• Sulphur Mountain Cosmic Ray Station in Canada
• Sputnik 1, the first-ever satellite
• Sputnik 2, with a canine passenger
• Explorer 1, the first US satellite
• Explorer 2, a launch failure
• Explorer 3, which helped discover the Van Allen radiation belt

    

Perhaps the world can use more collaborative efforts like the IGY.

Blogroll: Astronomy Picture of the Day

The NASA Astronomy Picture of the Day always has something spectacular. The picture above, from 21 December last year, shows a montage of images taken at different wavelengths by NASA’s Solar Dynamics Observatory. The wedges run from 170 nm (UV, shown in pink) through 9.4 nm (X-rays, shown in green), with the background image taken at visible wavelengths. Some of the wavelengths highlight features of the solar surface very well.

Update: NASA also has a beautiful video version of this image (hat-tip to sparkonit):

WSC 2013: Final Reflections

Now that the World Solar Challenge is over for another two years, it’s time to reflect on the results, before I get back to my regular blogging.

	The Bridgestone World Solar Challenge team has once again organised an excellent race, which covered an entire continent (although there were some unfortunate hiccups with the timing board and with the Silverlight-based live streaming of the awards).
	The Nuon Solar Team deserves to be congratulated, for having the fastest car in the Challenger Class (followed by Tokai University and Solar Team Twente). Effective strategy (including planning for the weather) was also critical to reaching the finish line first. My race chart shows how close the battle for first place was.
	Solar Team Eindhoven, winner of the Cruiser Class (see my updated post about the results), has shown that practical solar cars (carrying multiple people) are not all that far away from commercialisation. All kind of interesting applications can be imagined for vehicles like “Stella” – or indeed vehicles like the equally interesting Sunswift eVe or PowerCore SunCruiser.
	The Netherlands has demonstrated strong expertise in solar car technology, with centres of excellence at Delft University of Technology, Eindhoven University of Technology, and the University of Twente. The Netherlands took out the Challenger #1, Challenger #3, and Cruiser #1 positions in the race. Other European teams took out Challenger #5, Challenger #6, and Cruiser #2 – it was a European-dominated event.
	Jeroen Haringman at solarracing.org has done a superb job of analysing the race as it was happening, integrating information from both the official race site and from individual team blogs. When an event spans an entire continent, it’s difficult to get an overall perspective on what’s happening, unless someone does this kind of analysis. The organisers provided some of the raw data (GPS position and timing), but various photos, videos, and comments by participants were scattered around cyberspace, and required collating. One commenter called Jeroen Haringman’s site “the only comprehensible record.”
	The individual media teams did a great job in communicating the excitement around the world via YouTube, Twitter, Flickr, and blogs. The media teams of Twente (Dutch video) and Nuon (Dutch video with captions) did particularly well. With enough technology, it becomes almost like being there.
	GPS feeds into Google maps were an effective way of covering the race, although varying forms of analysis that were being built on-the-fly during the race need to be developed further. A short-lived experiment with Google Docs was particularly interesting, though limited in several ways.
	A “brave attempt” award goes to the two high-school entries, from Goko High School in Japan (their nice-looking Cruiser Class entry lost its rear wheels just outside of Alice Springs), and Choctaw Central High School in Mississippi (their sleek Adventure Class entry developed electrical problems between Katherine and Dunmarra). For a high school to even compete at this level is indeed a major achievement!
	The sun has really been the star of the race. It provided the energy that powered the vehicles. But the pictures of the Tokai vehicle stalled in the rain on the morning of the fifth day are a reminder that the sun is not always available. The first three days of the race took place in a part of the world with an average insolation of around 250 W/m2. In cloudier regions and at higher latitudes, average insolation drops to less than half of that, as well as being less consistent. That means that energy storage will always remain a critical part of any solar technology. It also means that solar technology is perhaps better suited to some parts of the world than others.

Finally, let me finish my WSC race coverage with this parting photo (by Jorrit Lousberg) of Team Nuon in the outback. It’s been an exciting week!

No wonder it’s cold down here

Here in Australia, it’s the middle of winter. And, as Bad Astronomy reminds me, we’ve also just had aphelion, Earth’s furthest point from the sun (152 million km, compared to 147 million km at closest approach). The diagram below exaggerates the elliptical nature of Earth’s orbit, but it gives the general idea:

For the current distance to the sun, see Wolfram’s calculator or the live diagram of the solar system at Fourmilab, which includes images (green lines show orbits below the plane of the ecliptic):

IRIS launches on a flying horse

A few days ago NASA launched the Interface Region Imaging Spectrograph space probe for solar UV astronomy, using a Pegasus rocket. The video below shows the launch – Pegasus launches off an L-1011 carrier aircraft at 40,000 feet, which avoids (among other things) a lot of weather problems:

Blogroll: Bad Astronomy

Bad Astronomy, one of the blogs I follow, is celebrating the summer solstice today. Down under here in Australia it’s the winter solstice, of course. Altogether a colder sunlight.