The new moon arrives Friday (July 9), a day after the planet Mercury reaches its highest elevation in the morning sky.
The moon is officially new at 9:16 p.m. EDT (0116 July 10 GMT), when the moon is directly between the sun and Earth. Technically, both objects are in conjunction, meaning that they are on the same north-south line that passes through the celestial pole, near the star Polaris. (The term conjunction is also applied to other celestial bodies, such as planets). The timing of the lunar phase depends on where the moon is relative to the Earth, so the new moon occurs at the same time all over the world — the only differences being due to what time zone you are in — in Melbourne, Australia, for example, the new moon occurs at 11:16 a.m. on July 10.
Since the new moon is between Earth and the sun, it isn't visible unless there is a solar eclipse (when the new moon passes in front of the sun), and the moon and sun rise and set at nearly the same time. Solar eclipses don't happen with every new moon because the orbit of the moon is slightly tilted, by about 5 degrees, relative to the plane of the Earth's orbit, which means that it doesn't always pass exactly between the sun and Earth — the moon's shadow "misses" our planet. (The next solar eclipse isn't until Dec. 4, 2021).
Related: The brightest planets in July's night sky: How to see them (and when)
Visible planets
In the predawn hours of Thursday (July 8), the planet Mercury will be at its highest altitude above the horizon for this appearance, and it will also be in conjunction with the 28-day-old moon. The moment of conjunction happens at 12:39 a.m. EDT (0439 GMT), so the moon will be past its closest approach by the time the pair is visible in New York City, when they rise at 4:08 a.m. local time, according to sky-watching site In-The-Sky.org.
By sunrise Mercury will be at an altitude of about 14 degrees in the constellation Taurus, the bull, to the right of a very thin crescent waning moon. Mercury is about as bright as the star Vega; at magnitude 0. The best time to catch it will likely be about a half-hour after it rises when it is about 5.5 degrees above the horizon and will appear to the right of the moon. Take care when observing planets so close to the sun; even at sunrise accidentally focusing on the sun with a pair of binoculars can cause permanent retinal burns and possibly blindness.
Observers closer to the equator will have an easier time seeing Mercury. As one moves to low latitudes (either from the north or south pole) the ecliptic — the plane of the Earth's orbit projected on the sky — makes a steeper angle with the horizon. That means the planets, which all wander within a few degrees of the ecliptic, tend to reach higher altitudes. From Quito, Ecuador, for example, the conjunction occurs Wednesday (July 7) at 11:39 p.m. local time, and Mercury and the moon will rise at 4:50 a.m. Sunrise is at 6:16 a.m., and by 6 a.m. the two bodies will be about 16 degrees in altitude.
Venus, meanwhile, appears as an evening star for the next few months, and on July 9 will be visible after sunset from New York City until it sets at 10:01 p.m. local time. At sunset (8:28 p.m. local time in New York) the planet will be about 17 degrees above the west-northwestern horizon. An interesting exercise is to see how soon after sunset you can spot it. Mars will also grace the evening sky — on the night of the new moon the planet will be just to the left of Venus, though harder to spot as the Red Planet is fainter than Venus and won't be visible until at least 15 to 20 minutes after sunset; by that time the planet will only be 14 degrees above the horizon. The two planets will be about a degree apart, or two lunar diameters.
On Monday (July 12) the moon will make a close pass to both Venus and Mars. The new crescent moon will be in conjunction with Venus on July 12 at 5:09 a.m. EDT (0909 GMT) and passes about 3 degrees to the north of the planet. About an hour later, at 6:10 a.m. EDT (1010 GMT), the moon will pass just under 4 degrees (3 degrees 46 arcminutes) to the north of Mars. From North America the conjunctions won't be visible, but by sunset the two will be a little further apart but Venus will be to the right and below the moon.
If you live in Asia or the Western Pacific the moment of conjunction will be visible while Venus and Mars are above the horizon. In Tokyo, for example, the conjunction with Venus occurs July 12 at 6:09 p.m. local time, about 50 minutes before sunset, which happens at 7 p.m. local time. The conjunction with Mars is at 7:10 p.m.
In Melbourne, Australia, the Venus conjunction happens at 7:09 p.m. local time and the sun sets at 5:17 p.m., so by 5:30 p.m. the two will be about 18 degrees high in the northwest as the sky darkens. The Mars conjunction is at 8:10 p.m. local time.
Constellations
On the night of the new moon (July 9) Saturn rises at 9:45 p.m. in New York and is in the constellation Capricornus, the sea goat; it reaches the meridian (its highest point in the sky) at 2:39 a.m. local time on July 10. Capricornus is a relatively faint constellation, so in areas with a lot of light pollution Saturn stands out in the southern sky.
Jupiter, meanwhile, rises about 55 minutes later at 10:40 p.m. local time in New York; it is also located in a fainter constellation, Aquarius, the water bearer. From mid-northern latitudes Jupiter and Saturn will reach altitudes of about 35 and 31 degrees, respectively, and Jupiter will be to the left (east) of Saturn.
Antipodean skywatchers will get a much better view since the winter months mean that the ecliptic is at a much steeper angle relative to the horizon from places like Australia or New Zealand. From Melbourne, Jupiter will get as high as 64 degrees above the northern horizon in the wee hours of July 10, and Saturn will also be as much as 70 degrees high — nearly straight up by the time it crosses the meridian at 2:06 a.m. local time.
July is the time for summer constellations in the Northern Hemisphere, and that means that by 10 p.m. the Summer Triangle has cleared the horizon and is high in the eastern sky. The Summer Triangle consists of the stars Deneb, Altair, and Vega, which make a rough right triangle with Altair at the southern end. By 10 p.m. local time Vega is 63 degrees in altitude, and it is the highest of the three stars.
Looking north, one will see the Big Dipper to the left (west) of Polaris, the pole star. Following the "pointers" to Polaris and continuing straight across you encounter Cepheus, the king, and just below Cepheus the "W" shape of Cassiopeia.
In the other direction, follow the handle of the Big Dipper and "arc to Arcturus" (the brightest star in the constellation Boötes, the herdsman), and continuing downward you hit Spica, the brightest star in Virgo. Turning south, one sees the bright red star Antares, the heart of the constellation Scorpius, the scorpion, and in darker sky locations looking up (north) from Scorpius one sees the constellation Ophiuchus, the snake bearer.
In the southern latitudes, the sun sets earlier (it being austral winter) and by 7 p.m. the sky is dark and the Southern Cross constellation is high in the south. To the left of the Cross (east) is Alpha Centauri, our nearest stellar neighbor, and east of that is Scorpius, though upside-down (from the point of view of a Northern Hemisphere observer). In the southwest, the "ship's keel" Puppis, is setting and marked by Canopus, the second-brightest star in the night sky after Sirius. In the same region of sky are the Large Magellanic Cloud and Small Magellanic Cloud, two satellite galaxies of the Milky Way.
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