Last modified: Tuesday, June 1, 2004
Venus to transit the sun on June 8
BLOOMINGTON, Ind. -- Venus will be sinking below the treetops in the west-northwest at nightfall as June begins. But on June 8 something extremely rare will happen: Venus will pass across the face of the sun as seen from Earth, an event called the transit of Venus. That hasn't been seen since 1882, when it caused great excitement among astronomers and the public.
The entire transit will be visible in most of Asia, Africa and Europe. Observers with suitable filters to protect their eyes will be able to see Venus as a black dot moving across the sun's bright disk for almost six hours. The planet will be three quarters through its crossing by the time the sun rises over the eastern coasts of North and South America. For a map of where the transit will be visible, see http://sunearth.gsfc.nasa.gov/eclipse/transit/venus/Map2004-1.GIF. More information about the transit of Venus, including how to observe it safely, is available at http://skyandtelescope.com/observing/objects/article_1258_1.asp.
Be sure not to look at the sun directly without a solar filter, such as a piece of No. 14 welder's glass, the traditional choice. This safe filter material can be bought for a few dollars at any welding supply store.
Normally, Venus is either slightly above or slightly below the sun's disk when it passes between Earth and the sun in its smaller, faster orbit. Only rarely does it pass directly across the face of the sun. There will be another transit of Venus in 2012, but the next after that will be in 2117.
The transit of Venus was important to 19th century astronomers because it offered a chance to accurately measure the distance from Earth to the sun. That was the basic unit of astronomical distance at the time. It has since been replaced by much larger units as the frontiers of astronomy have expanded outward into the universe.
After the transit of Venus on June 8, the planet will reappear during the last week of the month above the east-northeast horizon an hour before dawn, close to the bright orange star Aldebaran.
Jupiter will dominate the evening sky in the southwest after sunset during June, outshining all the stars in the constellation Leo the Lion. Jupiter will be easy to spot until it sets in the middle of the night.
Much lower in the west-northwest at dusk will be Saturn and Mars, in the constellation Gemini the Twins with its bright stars Pollux and Castor. Pale orange Mars will be below Pollux on the left (south), and much brighter Saturn will be roughly below Castor. As June progresses, Saturn will be lower each night while Mars will seem to hold its position. By the end of the third week, Saturn will be out of sight in the solar glare and Mars will form a nearly straight line with Pollux and Castor to its right.
Look well to the left of Saturn and Mars to spot the bright white star Procyon. Farther to the right of Saturn and Mars will be bright yellow Capella.
Mercury will be out of sight during June as it passes behind the sun.
Viewing information and graphics for the planets are available at http://www.space.com/spacewatch.
The brightest star high in the east-northeast after dark will be Vega. The brightest star to its lower left (north), by two or three fist-widths at arm's length, will be Deneb. About the same distance to Vega's lower right (south) will be Altair rising in the east. These three stars form the huge Summer Triangle, which will cross the sky high overhead during the night.
The sun will reach the June solstice on June 20 at 7:57 p.m. CDT (June 21 at 00:57 Universal Time), marking the start of summer in the Northern Hemisphere and winter in the Southern Hemisphere. For the next six months in the Northern Hemisphere the days will be getting shorter.
Officially the first day of summer, the June solstice is also referred to as Midsummer because it is roughly the middle of the growing season throughout much of Europe. Most societies in the Northern Hemisphere, ancient and modern, have celebrated a festival on or close to the June solstice. The themes common to all of these festivals are fertility and agriculture.
"Solstice" is derived from two Latin words: sol meaning sun, and sistere, to cause to stand still. This is because the sun rises higher in the southern sky each day until the summer solstice. On the day of the solstice it appears to rise to the same height as the day before, and in the days afterward it is lower, heading back toward its low point at the winter solstice. In this sense, the sun "stands still" for one day at the peak of its journey across the summer sky.
This time of year, between the planting and harvesting of the crops, was the traditional month for weddings. June remains a favorite month for marriage today. In some traditions, newly wed couples were fed dishes and beverages that featured honey for the first month of their married life to encourage love and fertility. The surviving vestige of this tradition is the name given to the holiday immediately after the ceremony, the honeymoon. The first full moon in June is sometimes called the Honey Moon.
The moon will be full on June 3, at third quarter on June 9, new on June 17 and at first quarter on June 25.