On Nov. 3, 1973, Mariner 10 was launched, becoming the first spacecraft to study the planet Mercury and also the first to use the gravity of one planet, in this case Venus, to “slingshot” it past one planet on the way to visit another. A more interesting first was that, as its fuel supply ran low, the solar wind was used as a means of locomotion as scientists manipulated the spacecraft’s solar panels as sails to make course corrections.

Mariner 10 made its initial flyby of Mercury on March 29, 1974, and two subsequent ones on Sept. 21, 1974, and March 16, 1975, each time photographing half of the planet’s surface, learning that 80 percent of the planet was a metallic core giving it a surprisingly strong magnetic field, and that temperatures at the surface ranged from 187 (day) to -183 (night) degrees Celsius. With its power source all but dead, Mariner 10 was shut down on March 24, 1975, and is still orbiting the sun.

Focus on the planets

Mercury is low in the northwest about an hour after sunset, situated far to the lower right of Jupiter. It is lost to view by the end of the first week of June.

Venus opens June low on the eastern horizon just before daybreak but rises a bit higher in the sky throughout the month. While still the brightest object in the morning sky but for the moon, surface features are indistinct even by telescope.

Mars is well up in the southwest as dusk deepens to nightfall and is four times brighter than its nearest neighbor, blue-white Spica of Virgo.

Although Earth is outdistancing its slower, outer neighbor, surface features of Mars are still distinguishable with a medium-sized telescope. Be sure to check out the close approach of Mars and the moon on June 7.

Jupiter rises in the west at dusk and sets three hours after the sun as June opens. This window of opportunity to view the giant planet and its moons decreases to less than an hour by month’s end. On June 1, Jupiter is situated just to the lower right of the waxing crescent moon with Castor and Pollux hovering above.

Saturn rises in the south at nightfall and remains in view through most of the night. The rings are tilted at 21 degrees to our line of sight, offering great viewing opportunities, as does its major moon Titan, which orbits the planets every 16 days.

Uranus rises in the east about an hour after midnight and its blue-green disk, located in Pisces, is observable with a good set of binoculars.

Neptune comes up in the east-southeast among the stars of Aquarius, where its blue-gray disk can be seen by telescope. Observers can visit the Sky and Telescope website, skypub.com/urnep, to help spot these far distant worlds.

June events

1 Sunrise, 4:53 a.m.; sunset, 8:14 p.m.

2 Jupiter dominates the western horizon about an hour after sunset with the Twins, Castor and Pollux, to its upper right. It is possible you might see faint Mercury very far to Jupiter’s lower right, hovering just above the horizon.

3 Moon at apogee, or farthest distance from Earth, today.

5 Moon in first quarter, 4:39 p.m.

7 Mars stands just to the upper right of the moon, high on the southern horizon, an hour after sunset.

10 Saturn is to the upper right of the moon, high in the south-southwest, an hour after sunset.

13 Full moon, 12:13 a.m. The full moon of June is called the Strawberry Moon or the Rose Moon.

15 The moon is at perigee, or nearest approach to Earth, today.

16 The June Lyrid meteor shower is listed for tonight, but they might not still exist, as the last sighting of a sparse shower was in 1996.

21 Summer solstice, 6:51 a.m. The sun has reached its northernmost point above the equator and will begins its journey south, bringing shorter periods of daylight and the inevitable approach of fall. The sun enters Gemini on the ecliptic and the astrological sign of Cancer.

24 Look to the pre-dawn eastern horizon for Venus and the crescent moon in close proximity.

27 The Bootid meteor shower peaks tonight. These last had a good display in 2004, with 50 meteors per hour, and not many are expected this year. However, their coinciding with a new moon will help see what few may appear. New moon, 4:08 a.m.

29 Jupiter is very low in the west about 45 minutes after sunset with the crescent moon to its upper left.

30 Sunrise, 4:52 a.m.; sunset, 8:25 p.m. The moon is at apogee for the second time this month.

Send astronomical queries to Clair Wood at cgmewood@aol.com.