The Shadow of Venus

The shadow of Venus will fall on the earth this month, on Tuesday, June 8, as Venus passes directly across the face of the sun.

Unfortunately, San Jose won't be covered by that shadow: you'll have to travel at least as far as the east coast of the US, and preferably to another continent, to view the transit.

So why talk about it? Mostly because it's an extremely rare event: no living human has seen a Venus transit.

The last Venus transit took place in 1882. They come in pairs, for reasons buried in the arcana of celestial mechanics, so there will be another one this century, on June 6, 2012; that one will be visible from San Jose, where the sun will set with the transit still in progress.

Get more information on times and locations at this NASA site: http://sunearth.gsfc.nasa.gov/eclipse/transit/TV2004.html

When an inner planet (meaning Venus or Mercury) transits the sun, the planet's shadow is visible as a sharp black spot against the sun's disk. Of course, this means that you need a safe solar filter to view it; the sun is just as bright as ever during a transit, and just as damaging to the unfiltered eye.

Some of you may remember the Mercury transit of a few years back, which was visible from San Jose. The Venus transit should be more impressive -- Venus is both bigger, and closer, than Mercury. In fact, Venus' silhouette is big enough that it should be easily visible without magnification, using only a solar filter held up to the eye.

There's not much else going on in the system that's visible from our corner of it. Of course, the sun is always visible: use your newly purchased solar filter, or that old one gathering dust in the garage, to take a look at this month's collection of sunspots. The sun isn't as active this year (so far) as the phenomenal activity we saw last year, but there still should be sunspots visible on most days.

Jupiter stands in the western sky at dusk, setting about midnight. It's much lower than it was last month, and it will be more difficult to see detail in its cloud layers, but its moons and moon shadows should be just as visible as ever.

Pluto, still in Ophiuchus, is at opposition on the 11th at magnitude 13.8. It's within reach of amateur telescopes; a practiced observer from dark skies should be able to locate it with a 10" or 12" telescope, though first-time Plutocrats may have better luck starting with more aperture. The important thing is to use a good finder chart; the chart in the RASC handbook has proved very reliable.

Uranus, in Aquarius, and Neptune, in Capricornus, trail Pluto by several hours, and are visible in the morning sky.

Mercury is too close to the sun this month for good observation; Venus, of course, is even closer early in the month, but moves into the morning sky during the latter half of June. The summer solstice falls on June 20th.

If you can't watch the transit in person, try catching it on one of the live webcasts. The Exploratorium in San Francisco will be showing live video from the event. For home viewers, it's hard to predict which web sites will have the best webcast; big events like this may overwhelm some sites, so try a few different sites.