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Planets to huddle in western sky

A triad of planets dance together in the western sky at dusk this month. This beautiful and rare cluster of planets can be seen to change their relative positions as each new night unfolds. The brightest of the trio is Venus, followed by Jupiter and then the much fainter Mars.

My favorite time to observe would be on the evenings of the June 14 and 15 when the crescent moon also makes its debut _ then again on Monday, June 17 when they are all within 1.8 degrees. This is close enough that under low power all three may be seen at the same time in a telescope (or binoculars).

Compare the brilliant white of Venus with the cream of Jupiter and the orange-reddish hue of Mars.

Even though the trio appear close in the sky, they are many millions of miles apart in actual space. Venus is the closest, then Mars, and finally Jupiter is the most distant.

Venus is clearly the most brilliant evening star in the west. As the planet moves toward us, its angular size is increasing and its phase waning.

With a telescope it can be seen to undergo phases just like the moon and will be half full about the 12th. These phases were first seen by Galileo in the 1600s and gave evidence to the fact the Earth moves around the sun.

Venus will also be at greatest elongation on June 13, when it will be at its greatest angular separation from our sun. Venus is about the same size as the Earth and owes its brilliance to its close proximity to the Earth and its cloud-covered surface.

Jupiter will be seen as the second brightest evening "star" in the west.

If you are using binoculars, look for up to four bright points of light near it; these are its four largest moons. They are 2,000-3,000 miles across. Jupiter itself is more than 10 times the diameter of Venus, but it is by far the more distant.

In the beginning of the month it will be the highest of all three planets, and by the end of the month it will be the lowest.

Mars is clearly the faintest of our trio and also the smallest. It is only half the diameter of the Earth and is now at its greatest distance from the sun.

Look to see how close it is to Jupiter the evening of June 13. Get out your binoculars on June 6 and 7 and see Mars suspended in front of the Beehive Star Cluster (Praesepe) in the constellation Cancer. Mars is some 150-million miles away while the star cluster is 3,000-trillion miles away.

Saturn can be seen in the southern sky before dawn in the constellation of Capricornus. It rises about midnight during the first of the month and two to three hours earlier at the end of the month.

The sun will be found at its northernmost point on June 21, marking the summer solstice. You may wish to observe its setting a week before and a week after this date to see for yourself that it sets at its northernmost point on the horizon on this date.

It is at this time that we have the most hours of daylight in a 24-hour period. This begins summer in the Northern Hemisphere and winter below the equator.

Daryl L. Schrader is an astronomy and mathematics professor at St. Petersburg Junior College and teaches astronomy at the University of South Florida.

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