Mercury makes pass at sun

The Sky Guy

Posted: Sunday, November 05, 2006


  Graphic courtesy of Andy Veh

Graphic courtesy of Andy Veh

The most exciting astronomical event this month is the Mercury transit on Wednesday from 10 a.m. to 3 p.m. I will have telescopes set up on the Kenai Peninsula College front lawn, equipped with proper solar filters. Mercury will appear as a tiny disk against our sun’s huge disk. People stopping by at my telescopes are usually amazed by how huge our sun is compared to a planet (Earth wouldn’t appear much bigger).

Only the two inner planets, Mercury and Venus, can get between us and our sun. Because their orbits are tilted — and despite the fact that they only need 88 days and 225 days, respectively — such so-called transits are rare (because usually they orbit too high or too low). Mercury transits every seven years on the average but Venus only twice every 130 years or so. I was able to see a Venus transit in June 2004 from Barrow and plan on the 2012 one seen from Alaska, as well. In the meantime Mercury transits once more (after the recent ‘99 and ‘03), which can be seen at least partially during sunset or sunrise from all of the Americas, East Asia, Indonesia and Australia, and completely from Alaska, the Western U.S., Canada and Hawaii. Photos of the last Mercury transits in November 1999 and May 2003 can be seen at my Web page by clicking on my planet lecture. This is Mercury’s last transit until 2016.

Winter has almost arrived and that means that the bounty of the beautiful winter sky charms us once more. The accompanying chart is set for 10 p.m. in early evening and midnight in late November (notice also that south is at lower left), thus more stars will have risen in the earlier evening hours later this month.

Orion, Taurus, Gemini and Auriga are rising in the east. With them are the bright stars of winter: red Betelgeuse and Aldebaran, blue Rigel, yellow Capella and next to the twins’ Pollux and Castor appears Saturn, its rings nicely seen in a small telescope. Also included in the chart is the star cluster of the Pleiades, best viewed with binoculars, when up to 50 stars may be seen.

Soon the bright stars Procyon and Sirius will follow. Now in the Zenith are Cassiopeia’s W and the House of Cepheus. Always in the same place is the Little Dipper with Polaris, and toward the northern horizon appears the Big Dipper. The kite-shaped Bootes is now setting while the summer triangle consisting of Deneb (the Swan’s tail), Vega and Altair is getting closer to the western horizon but will be visible until January since Deneb and Vega are circumpolar in Alaska (they never set).

Apart from watching Mercury during an unusual time — broad daylight — Saturn is the only planet that can be easily seen this month. It rises in the northeast around midnight in early November and around 10 p.m. late in the month. High-power, stable binoculars or a telescope are needed to view its rings.

The Leonids, now a weaker meteor shower, will show during the night of Nov. 17/18.

Our moon will show us an interesting spectacle. On and around Tuesday (plus or minus two days), the moon will be almost full, will rise at 4:25 p.m. and not set until 2:45 p.m. the next day, which means the moon can be seen for 22.5 hours straight. I call this the “Midday Full Moon” as the winter moon’s answer to summer’s Midnight Sun. This can only happen in northern latitudes and only in winter.

For the same reason that the sun can stay up virtually all day when it is in Taurus in late June, the full moon appears in Taurus and Gemini and is up just as long. In fact, since its orbit is tilted by 5 degrees, that pushes the latitude of the midnight sun from the arctic circle (67 degrees, Coldfoot) to 62 degrees (Talkeetna) and even further south because atmospheric refraction makes the moon appear even above the horizon as seen from the Kenai. The same event repeats in early December. (See also an article about this by Ralph Hulbert, moon.htm, in the Anchorage paper two months ago.)

Andy Veh is the physics and astronomy instructor at Kenai Peninsula College. He can be reached at

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