Saturday, June 30, 2012

Leap Second: Today is the Longest Day of the Year

Due to the gradual slowdown in Earth's rotation, a team at the Paris Observatory is adding a "leap second" just before midnight. Experts at the International Earth Rotation and Reference System Service make the adjustment when the planet's movement falls out of sync with atomic clocks used to measure time.

 "Today, time is constructed defined and measured with atomic clocks" said Noel Dimarcq, director of the SYRTE time-space reference system at the Paris Observatory. "This allows us to ensure that everyone on Earth is on the exact same time," Daily Mail quoted Dimarcq as saying. 

Today's final minute (Greenwich Time), with its added second, will compensate for the sloshing of oceanic tides on the continental shelves, which slows Earth's rotation ever so slightly. It's been four years since a leap second has been added.

Wednesday, June 20, 2012

Closure of 70 of California's State Parks

The First 70 Trailer from Heath Hen Films on Vimeo.

On July 1st, up to 70 of California’s 279 state parks may be closed due to budget cuts enacted by the Governor and Legislature. This closure will affect 25% of California's beautiful parks will erode the state’s commitment and legacy to irreplaceable natural, cultural, and historic resources. Additionally, closing state parks will impact California’s travel and tourism industry and reduce much-needed revenues for local businesses. As the parks are shut down they will no longer be considered in the state's eyes as an asset, which will allow for lobbyists to push to have state protection of the parks removed. This will allow for timber, mining, and real estate interests to purchase bits of the parks. Although this will profit them immensely, it will devastate the national landmarks and leave the land ravaged.

Monday, June 4, 2012

Transit of Venus!

There will be a "transit of Venus" on Tuesday, June 5, visible from throughout the USA. (It will occur on June 6 in Asia, across the International Date Line.) Venus will look like a tiny black dot on the Sun. The last time this occurred was in June 2004. After June 5, 2012, to see the transit of Venus anywhere on Earth you'll need to wait until the year 2117, and then 2125 – no kidding! (The previous pair of Venus transits was in 1874 and 1882.) So, I suggest you see it!

A transit of Venus occurs when Venus passes right between Earth and the Sun: it looks like a tiny black dot, about 1/30th the size of the Sun (more technically, about 1 arcminute in diameter), slowly going across the Sun. You'll be able to just barely see it with the unaided (but protected) eye, but a far better, magnified image will be visible if you look through binoculars (properly filtered) or a telescope (again, properly filtered). If you wish, you can get very nice, appropriate equipment at many stores, such as Scope City. Wherever you live, local amateur astronomy organizations and science centers will set up telescopes for public viewing, you'll just have to check online for locations. The Chabot Space and Science Centerin the Oakland hills is one such example.

In the Pacific Daylight Time (PDT) zone, the transit starts on June 5 at about 3:07 pm, though it will be hard to notice until around 3:24 pm. Mid-eclipse will be at 6:27 pm. In the San Francisco Bay Area, sunset occurs around 8:28 pm. The transit ends at 9:47 pm PDT, after sunset in California. As with the partial lunar eclipse above, if you are in other time zones, adjust the times accordingly. These times are, of course, approximate to within a few minutes, however they will depend slightly on your exact location within a time zone. So, progressively less of the transit will be visible the farther east you go in the USA.

Suppose you consider the Sun’s disk to be like the face of a clock when you look directly at it. As seen from San Francisco and most of the USA/Canada, Venus will begin to transit at roughly the 12 o’clock position (i.e., near the top of the Sun), but around sunset, Venus will be near the 4 o’clock position. More information on the event can be found at, and

Transits of Venus are historically important because observations of them in 1761 and 1769 from many different locations on Earth led to the first accurate (to within 2%) estimate of Earth's distance from Venus, and hence of Earth’s distance from the Sun (the “Astronomical Unit”) since the relative distances were already known. Viewed from a given location on Earth, the exact position of Venus’s silhouette depends on Venus’s distance, so one can solve for the distance using a bunch of measurements. Transits of Venus are important now because they illustrate the technique with which thousands of exoplanets are being found by the Kepler spacecraft: the total brightness of a star periodically drops a tiny bit while an exoplanet transits across its disk, as seen by us. If you monitor a star’s brightness and notice a slight periodic dimming, you’ve probably detected an exoplanet.

If you are planning on looking directly at the Sun, remember that you need proper eye protection or you could permanently damage your eyes! Use "Shade 14 welder's glass" (available at welding supply stores) or some other safe filter which blocks 99.999% of the Sun's rays at visible, ultraviolet, and infrared wavelengths. Appropriate "eclipse glasses" can also be found and purchased online for just a few dollars (comparable to Shade 14 welder's glass, but less durable). Regular sunglasses or smoked glass won't suffice by a long shot.

Without magnification, the black silhouette of Venus will be barely visible to the naked eye, or possibly even invisible, depending on your visual acuity. A magnified view will be much better. If you have a sufficiently small pair of binoculars, you can securely tape a piece of Shade 14 glass across the front end (so that light goes through the filter before entering the binoculars). Many local amateur astronomy clubs and science centers will have properly filtered telescopes for public viewing, providing a magnified image. I encourage you to visit them and watch the transit safely.

Saturday, June 2, 2012

Upcoming Partial Lunar Eclipse

On the morning of Monday, June 4, there will be a partial eclipse of the full moon in the few hours before sunrise. About a third of the Moon will enter the Earth’s dark shadow, starting at 3:00 am PDT and ending at 5:06 am PDT (mid-­‐eclipse at 4:03 am PDT). No optical aid is needed to view the eclipse, though binoculars or telescopes will provide a magnified view. There is no danger when viewing a lunar eclipse with the naked eye, binoculars, or telescopes; filters are not needed (unlike the case for a partial solar eclipse). Just go outside wherever you are, and take a look! But some local astronomy clubs and science centers (such as the Chabot Space and Science Center in the Oakland hills) will hold official public viewing sessions; check online.

The entire easily visible part of the eclipse (when the Moon is in the Earth’s “umbra,” or full shadow) will be visible from California. As seen from the central USA, moonset will occur during the eclipse. The eastern US will basically miss out on this eclipse, since it will begin around or after moonset. West of California (say, in Hawaii), the entire eclipse [penumbra (partial, bright shadow) and umbra (full, dark shadow)] will be visible with the Moon high in the sky. For more information, see (courtesy of Fred Espenak, NASA’s GSFC.