July is the first full month of summer and we should have some great nights to view the heavens. The month is named after Julius Caesar.

Highlights include Earth being farthest from the sun, nice conjunctions of the moon with Mars and Saturn, three minor meteor showers, and the two biggest and brightest asteroids – Ceres, and Vesta – less than a quarter of a degree apart near Mars in the constellation of Virgo on the fourth of July.

Additional Images

SKY GUIDE: This chart represents the sky as it appears over Maine during July. The stars are shown as they appear at 10:30 p.m. early in the month, at 9:30 p.m. at midmonth and at 8:30 p.m. at month’s end. Saturn and Mars are shown in their midmonth positions. To use the map, hold it vertically and turn it so that the direction you are facing is at the bottom. Sky chart prepared by George Ayers

We will finally lose Jupiter early this month. The King of the Planets graced our evening skies all year. It will reach conjunction with the sun on July 24 and will turn up again in the morning sky next month.

Mars continues to fade as it falls farther behind Earth since its opposition in April. The red planet has been moving in its normal, direct, eastward motion since May and it will pass just over 1 degree north of Spica, the brightest star in Virgo, during the evening of Sunday, July 13. Notice that Mars is about twice as bright as Spica. Also be aware of the contrast with the orange-yellow hue of Mars and the bluish-white hue of Spica.

Located about 250 light-years away, Spica is a very interesting, rapidly rotating, blue giant variable star. That means that the light that left this star as you look at it this month left there around 1776, when we won the Revolutionary War.

It is also a double star, orbiting each other every four days. It is about 10 times the mass of the sun, 10,000 times as luminous as our sun, and four times its diameter. Greek astronomer Hipparchus used this star to figure out the precession of the equinoxes.

The first quarter moon will be less than half a degree below Mars and close to Spica on Saturday, July 5, one hour after sunset in the southwestern sky.

Then continue eastward along the zodiac into the next constellation, which is Libra. Saturn’s softly glowing golden hue will greet you there. The waxing gibbous moon will pass less than half a degree below Saturn on Monday, July 7, just two days after it passed very close to Mars. The ringed planet will end its westward or retrograde motion toward Mars and Virgo on July 21, one month after the start of summer. Mars is moving eastward much faster than Saturn, so it is catching up with the ringed planet at the rate of half a degree per day. Watch as the gap between these two planets shrinks from 28 degrees to 14 degrees this month. Mars will finally catch Saturn on Aug. 25.

Brilliant Venus rises about an hour and a half before the sun in the eastern sky in the constellation of Taurus, about 5 degrees above and to the left of Aldebaran, its brightest star. Located about 65 light years away, its name means “the follower,” since it rises just after the Pleiades. This orange giant star, which is about 40 times the size of our sun, is also known as the eastern royal star, one of four royal stars in the sky. If you could place Aldebaran where our sun is in the sky, it would cover 20 degrees of our sky. Its diameter is about 33 million miles, or one-third of the Earth-sun distance. It would reach about halfway to the orbit of Mercury, which is 36 million miles from the sun.

Venus will be at its faintest for the year this month, at magnitude minus 3.8. As it gets more illuminated by the sun, it also gets smaller and farther away from the earth. It will be 92 percent illuminated by the end of this month, approaching its superior conjunction.

Mercury will make an appearance below and to the left of Venus for most of this month. Notice that Mercury will be about 50 times fainter than Venus. It will be about half lit by the sun during the middle of this month.

The three minor meteor showers this month are the Alpha Capricornids, the Piscis Austrinids and the slightly better known Delta Aquarids, which peak on the 28th. Some early Perseid meteors will also be visible late this month, even though they don’t peak until Aug. 12.

Ceres and Vesta have been close together in the sky since May, but they will be only 10 arc minutes apart, which is one-sixth of a degree, on Friday evening, July 4. So when you watch the man-made, very short-term and nearby spectacle of the fireworks, think of the much more powerful, long-term and distant spectacle of these two largest asteroids. They are closer together from our line of sight that they have ever been in the history of humans on Earth.

Located safely in the asteroid belt between Mars and Jupiter, about 250 million miles away, both of these asteroids had the potential to become planets. The four largest asteroids make up half the mass of all the millions of asteroids in this belt.

Ceres is almost 600 miles in diameter, and Vesta is just over half that size. However, Ceres is not as bright as Vesta because it has much darker surface material and only reflects 9 percent of the sunlight back to us on Earth. Vesta has a medium gray surface and reflects 42 percent of the sunlight that strikes it, which is very high for an asteroid.

Ceres will be at magnitude 8.5 and Vesta will be at 7.2, so you will need good binoculars or a small telescope to see them for yourself. Completely invisible to even the largest telescope is the Dawn spacecraft that has already encountered Vesta and will take up a permanent orbit around Ceres to map its surface in the spring of 2015.

July highlights

July 3: Earth is at aphelion or farthest from the sun today for the year.

July 4: Pluto reaches opposition in Sagittarius tonight. It will only be 14.1 magnitude. On this day in the year 1054 the Crab nebula supernova was observed in the constellation of Taurus by all three major cultures on Earth at the time. It is still expanding quite rapidly almost 1,000 years later. On this day in 2005, the Deep Impact probe was purposely allowed to collide with Comet Temple 1. Ceres and Vesta will be only 10 arc minutes apart in Virgo tonight.

July 5: First quarter moon is at 7:59 a.m. EDT. Mars will be just south of the moon tonight.

July 6: Isaac Newton published his Principia on this day in 1687.

July 7: The moon will be just below Saturn tonight. The Mars rover Opportunity was launched on this day in 2003.

July 12: Full moon is at 7:25 a.m. This is also known as the Hay or Thunder Moon.

July 13: Mars will be just north of Spica tonight.

July 16: Apollo 11 was launched to the moon on this day in 1969. The first of 21 fragments of Comet Shoemaker-Levy 9 smashed into Jupiter tonight in 1994. The Dawn spacecraft went into orbit around Vesta to map this large asteroid and unveil some of its secrets on this day in 2011.

July 17: The first photo of a star was taken on this day in 1850. On this day in 1984, the Soyuz T-12 was launched, which became the 100th human space flight.

July 18: Last quarter moon is at 10:08 p.m.

July 20: On this day in 1969, Neil Armstrong and Buzz Aldrin became the first humans to walk on the moon.

July 22: The waning crescent moon will be close to the star Aldebaran in Taurus tonight.

July 24: The moon will be close to Venus and Mercury this morning. The Apollo 11 crew safely returned to Earth after its first lunar landing. The greatest and most meaningful thing the astronauts experienced was a true view of Earth floating in space and some of the profound implications that entails.

July 25: A thin crescent moon will be visible just below Mercury and Venus this morning.

July 28: The Delta Aquarid meteor shower peaks this morning.

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