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The Honolulu Advertiser
Posted on: Sunday, October 29, 2006

In rare event, Mercury will transit sun on Nov. 8

By Carolyn Kaichi
Bishop Museum

An unusual astronomical event will occur in November that favors the Hawaiian Islands, involving the smallest (official) planet and the most massive object of the solar system. Called the Mercury transit, this event is fairly rare and on average happens only 13 or 14 times a century. On Nov. 8, the tiny planet will pass in front of the sun over a period of almost five hours, and Hawai'i will have an ideal view of the entire transit.

There are only three objects between the Earth and the sun two planets and our moon. When the moon is in the right spot to block the sun from where you are standing on Earth, that's called an eclipse. However the two planets in "front" of us, Mercury and Venus, are much farther away than the moon. So when they line up between our position and the sun it's referred to as a transit, and what we see is a much smaller body passing in front of the sun's disk.

Most of the time Mercury and Venus pass a little above or below our line of sight because they are not in the same orbital plane as the Earth. Think of a dinner plate that represents our orbit around the sun. Take a second plate representing another planet's orbit and tilt it slightly. If you could somehow put those two plates together, you would see they intersect at two areas. Those areas are called nodes and it is only at those points that a transit can occur.

The two planets have to be in the same part of space for us to see a transit, though. Even if the inner planet is at the node, it doesn't help if Earth is not. Earth's orbital period is 365.26 days and Mercury's is 87.97 days, so the math is a bit complicated to get into here. Generally, the pattern of Mercury transits are usually paired and separated 3.5 to 13 years. This November transit is the second of the pair of which the last one occurred in 2003.

November's transit will begin shortly after 9 a.m. that Wednesday morning and finish shortly after 2 p.m. You will not be able to see this event without magnification and solar eye protection. Unless you are an experienced astronomical observer, please do not try to observe this on your own. It is very dangerous to view the sun, especially with magnification. The Bishop Museum, in partnership with the Institute of Astronomy and the Hawaiian Astronomical Society, will have solar telescopes on the grounds throughout the transit that day.

Why would you want to witness this transit? The last one in 2003 couldn't be seen from Hawai'i and the next one in 2016 will only be visible during the last few minutes before sunset. Because Mercury's apparent diameter is 194 times smaller than the sun, it was only observed after the invention of the telescope in the early 1600s, so sightings of this phenomenon is measured in the dozens even though it's been occurring since the formation of the solar system. The next Mercury transit that we can see in its entirety from Hawai'i will occur on May 10, 2062.

SCIENCE ON A SPHERE

There are big changes this month in the planetarium lobby. In March, we introduced our new Science on a Sphere, a six-foot-diameter screen upon which projected images from satellites and spacecraft could simulate views of our world and other planets from space. This month a new exhibit opens around the sphere concerning global warming on Earth.

Although there are still some skeptics, most scientists agree that humans have made a definite impact on the world's climate that will have consequences for the future of life on this planet. The Bishop Museum has taken the position that this is a real threat we face and everyone has some responsibility to do what they can at different levels. The new exhibit will address the science behind climate and weather and support the message of global warming with images on the sphere.

Not all of the exhibit will be ominous and serious, however. There will be lots of hands-on, interactive displays for visitors of all ages. The exhibit opens on Nov. 17 for Bishop Museum members and Nov. 18 for the public.

LEONID METEOR SHOWER

Another meteor shower viewing opportunity comes our way in November. The peak of the Leonids happens at 9 a.m. on Nov. 17, which is, of course, in broad daylight. So the early- morning hours of Nov. 16 and 17 will be suitable for viewing. Which night will be better is difficult to say, so you may have to check both nights. Leo rises in the east shortly after midnight and is also home to Saturn at the moment, so there's another reason to stay up.

THE PLANETS

  • Mercury: The reason Mercury will transit the sun this month is because it is going into inferior conjunction, or the point in its orbit where it passes in front of the sun. Because of Mercury's orbital tilt, we don't get a transit every time this occurs (four or five times a year) but only when the Earth and Mercury are exactly lined up in their orbits. On Nov. 1, Mercury is just above the western horizon at 6 p.m., right under Jupiter, but by the next few days will be too close to the sun to see at sunset. After the transit on Nov. 8, Mercury will reappear in the morning sky before sunrise.

  • Venus: Venus is still out of the picture as it makes its way back to the evening. Venus is between the orbits of Mercury and Earth, and isn't as quick to travel around the sun as Mercury. So in comparison to Mercury's 88-day "year," Venus travels around the sun in almost 225 Earth days. Keep in mind that a "day" on Venus is about 243 of our Earth days, making the Venus day longer than its year.

  • Mars: Mars is also traveling this month and not in the sky at all. Right now, it's behind the sun, from our perspective, and it will be at least another month before we see it in the sky again right before the sunrise.

  • Jupiter: The giant planet is just barely visible the first few days of November but is also heading toward the morning sky. It goes into conjunction with the sun on Nov. 21, so it is moving closer and closer toward the sun from our point of view and becoming more difficult to spot. It will re-emerge in the morning by early December.

  • Saturn: Thank goodness for Saturn coming back into the evening sky to give us some planetary sights this month. The ringed planet rises by 1:30 a.m. in early November, then just before midnight by Thanksgiving. With Venus creeping back into the evening sky as well, that gives us nighttime planet-watchers something to be thankful for.

    Use this map by holding it over your head so that its northern horizon points toward the northern horizon on the Earth. This illustration represents the sky at about 10 p.m. in early November, 9 p.m. mid-November and 8 p.m. in late November.

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