The July new moon offers dark skies to see 5 visible planets tonight (Image Credit: Space.com)
The new moon arrives on July 17, at 2:32 p.m. Eastern Time (1832 UTC), according to the U.S. Naval Observatory, two days before the waxing moon makes a close pass to Mercury.
New moons occur when the moon is directly between the sun and Earth. Technically, the sun and moon are in conjunction, on the same north-south line that passes through the celestial pole, near the star Polaris. Lunar phases’ timing depends on the moon’s location relative to the Earth, so they occur at the same time all over the world, with the hour changing according to one’s time zone: for Chicagoans the new moon is at 1:32 p.m. local time, while in Paris it is at 8:32 p.m., and in Tokyo it is at 3:32 a.m. July 18, and in Melbourne, Australia it is at 4:32 a.m. July 18.
New moons are not visible unless there is an eclipse; eclipses don’t happen every new moon because the orbit of the moon is tilted by about 5 degrees relative to the plane of the Earth’s orbit, and the point where the orbits intersect, called a node, moves relative to the Earth’s surface. That means the moon’s shadow “misses” the Earth most of the time. (The next solar eclipse is October 14, 2023).
And if you want to try your hand at photographing the moon and/or the night sky in general, check out our guide on how to photograph the moon, as well as our best cameras for astrophotography and best lenses for astrophotography.
Close passes to planets
On July 19, the moon will pass by Mercury as it emerges from the solar glare and becomes a thin crescent; the conjunction with the innermost planet will occur at 0857 UTC, or 4:37 a.m. in New York City. Neither the moon nor Mercury rises until after that, however – both rise at about 7:10 a.m. in New York according to In-the-Sky.org.
The moon will still be in close proximity to the sun; while it is possible, if challenging, to observe It during the day, that can be a dangerous thing to attempt – looking for objects near the sun with even modest optical aids can result in permanent eye damage and even blindness. It is far better to wait until sunset, which is at 8:23 p.m. local time in New York. At that point, the moon will be to the left of Mercury and above it; one can use the thin crescent, whose “horns” will be pointed away from the sun, to orient towards Mercury.
One will also see a bright planet to the left of the moon; that will be Venus, which is usually one of the very first objects to be visible in the sky as it gets darker. Mercury will still be hard to see; at sunset it is only about 9 degrees above the western horizon and the Sun is still likely to wash it out; the planet will only be about 4 degrees high by 9 p.m. local time when it should be just visible, but you will need a horizon that is relatively flat with no obstructions.
Spotting Mercury is somewhat easier as one moves to lower latitudes. As one moves closer to the equator (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 planets, which all move within a few degrees of the ecliptic, tend to reach higher altitudes. From Miami, for example, the conjunction occurs at the same hour (4:37 a.m.) as in New York City, but the sun sets slightly earlier, at 8:13 p.m. (Eastern Daylight Time) on July 19 and at that point Mercury is about 14 degrees high in the west, with the moon appearing about 5 degrees almost directly above it. About a half hour after sunset Mercury is about 7 degrees high and thus easier to spot than in New York.
From San Juan, Puerto Rico, the sun sets at 7:03 p.m. local time, when Mercury is 16 degrees high; Mercury is still 10 degrees above the western horizon by 7:30 p.m., with the moon directly above it and Venus to the left of both.
Southern Hemisphere observers will be able to see the pair earlier in the evening, as the days are shorter there (it being winter). From Buenos Aires, where the conjunction occurs at 5:57 a.m. local time, the sun sets at 6:03 p.m. on July 19, the moon will be 16 degrees high in the northwest, with Mercury a degree lower and to the left of the moon; Mercury will still be at 10 degrees by 6:30 p.m., before it sets at 7:33 p.m. local time.
While the two-day-old moon will pass Mercury, on the night of the new moon (July 17) with some luck and a flat horizon one can catch all five naked-eye planets over the course of the night. Mercury, for example, will be just visible in mid-northern latitudes after sunset, though without the moon to orient one might find it harder to see. For example, sunset in New York is at 8:24 p.m. and by the start of Nautical Twilight (when the sun reaches 6 degrees below the horizon) at 8:56 p.m. Mercury is only about 5 degrees above the horizon in the west.
Venus will be to the left, but it is much easier to see as it is about 4 degrees higher and some 45 times brighter than Mercury. Venus sets at 9:27 p.m. in New York; times will be similar in cities like Chicago, Columbus, Boulder, Colo., and Sacramento. Mars, meanwhile, will appear to the left of and above Venus; at sunset the planet is about 19 degrees high and sets at about 10:22 p.m. in New York. By about 9 p.m. local time one should be able to see Venus and Mars as a pair low in the west.
Saturn rises at 10:23 p.m., followed by Jupiter at 12:58 a.m. July 18. Both Saturn and Jupiter are in faint constellations; Saturn is in Aquarius and Jupiter in Aries, which means both will stand out – from most city locations (where the light pollution makes the sky background brighter) the two planets will be the easiest objects to see in their respective regions. Saturn reaches its maximum altitude at 3:52 a.m. and is about 39 degrees above the southern horizon; Jupiter doesn’t reach its maximum until after sunrise, but by 4:30 a.m. it will be about 39 degrees high in the east.
For the Southern Hemisphere’s mid-latitudes, the “evening stars” Mercury, Venus and Mars will be “flipped” with Venus almost directly above Mercury and slightly to the right, with Mars above Venus and to the right. For example from Melbourne, Australia, the new moon occurs July 18, and the sun sets at 5:21 p.m. local time. Mercury is 13 degrees above the northwestern horizon; by the end of civil twilight at 5:49 p.m. it is still about 9 degrees high.
Venus will still be 23 degrees above the horizon – the planet sets at 8:07 p.m. local time. Mars sets at 8:34 p.m. and is some 4 degrees above Venus. As Mars sets, Saturn rises, at 8:35 p.m., and Jupiter rises t 1:58 a.m. July 19. Both planets will be much higher in the sky than in the Northern Hemisphere; when Jupiter rises Saturn will b a full 62 degrees high above the northern horizon, reaching 63 degrees at 3:10 a.m. local time. Jupiter reaches an altitude of 37 degrees just before sunrise at 7:14 a.m. (the sun rises at 7:31 a.m. July 19).
For Northern Hemisphere skywatchers, July is the time for summer constellations. By 10 p.m. the Summer Triangle is high in the eastern sky; the “top” star is Vega, the brightest star in Lyra the Lyre, and it is almost at the zenith (about 68 degrees above the horizon). The other two stars in the Summer triangle are Deneb and Altair. Deneb is the brightest among a cross-shaped group of stars known as the Northern Cross; this is the backbone and wings of Cygnus, the Swan. Deneb marks the Swan’s tail – the very name means “tail” in Arabic (the word appears in similar names or other stars, such as Denebola, which is the tail of Leo the Lion). At about 10 p.m. Deneb will be to the left of and below Vega. Altair is the brightest star in Aquila, the Eagle, and is sometimes called its eye, with two fainter stars on either side of it marking the bird’s head. Altair will be to the right of Vega and below (south) of it; it’s the southernmost star in the Triangle and the last to rise. Deneb, Altair and Vega make a rough right triangle with Altair at the southern end.
Looking north (again at about 10 p.m. from mid-northern latitudes) one will see the Big Dipper to the left (west) of Polaris, the pole star. Following the “pointers” (the two stars in the front of the bowl of the Dipper, called Dubhe and Merak) to Polaris and continuing straight across you encounter Cepheus, the king, and just below Cepheus is the “W” shape of Cassiopeia; if one imagines the sky as a giant clock face, the Big Dipper is at 9 o’clock, Cepheus at about 3 o’clock and Cassiopeia at about the 4 o’clock position.
In the other direction, one can follow the handle of the big dipper and “arc to Arcturus” the brightest star in Boötes, the Herdsman, and continuing downward you hit Spica, the brightest star in Virgo, which will be in the southwest. Turning south (left), one sees the bright red star Antares, the heart of Scorpius, the Scorpion. Antares is relatively low in the sky; it won’t get more than 22 degrees high at the latitude of New York City.
That said, with a horizon free of obstructions one can see a curved string of stars extending from Antares down and to the left; this is the scorpion’s body and tail. In darker sky locations looking above (north) from Scorpio one can see a tall, thin, trapezoid of stars, which is the body of Ophiuchus, the Healer. To the left of Scorpius is a “teapot” shape of stars, this is Sagittarius the Archer (often rendered as a Centaur with a bow). Sagittarius is one of the southernmost constellations of the zodiac; from London (about 50 degrees north) it barely clears the horizon; from Stockholm only a few stars can be seen at all.
Moving back to Boötes, if one looks just above Arcturus, one can spot a rough pentagon of stars that is the Herdsman’s body or head (this depends a bit on the visualization one chooses). Just to the left of that is a medium bright star that is a medium-bright star called Alphecca; and it is part of a semicircle of stars that is Corona Borealis, the Northern Crown.
In the mid-southern latitudes, the sun sets earlier (it being austral winter) and by 7 p.m. the sky is dark and the Southern Cross is in the southwest – a full 61 degrees high. If one is facing south, to the left of the Cross (eastward) is Alpha Centauri, our nearest stellar neighbor, right next to Hadar (which is to the right, between Alpha Centauri and the Cross). Turning one’s gaze towards the horizon in the southwest, just about 13 degrees high is Canopus, one of the brightest stars in the sky. Canopus is also known as Alpha Carinae, as it is the alpha star of Carina, the Ship’s Keel. Looking just upwards is the large oval of stars that makes up Vela, the Sail – if one draws a line between Canopus and the Cross Vela is on the right side of the line.
If one turns eastwards from Alpha Centauri and Hadar one runs into Antares; from the southern skies the Scorpion is “upside down” but the constellation itself is much higher in the sky than from the Northern Hemisphere – Antares is about 61 degrees up from the latitude of Melbourne, Australia. If one follows the “hook” that is formed by the Scorpion’s body (this will trace a path roughly southeast) one encounters Sagittarius, which is about halfway to the horizon.
Next to Sagittarius on the right (west) is a fainter semicircle of stars that is Corona Australis, the Southern Crown. Further east the constellations are fainter – in a city location it is just possible to see Pavo, the Peacock, and to the right Octans, the Octant, which is near the Southern Celestial Pole; unlike the Northern Hemisphere there is no “pole star.” However, one can find the southern pole by using the Southern Cross; the long part of the Cross always points towards the pole, if not exactly, roughly five “cross lengths” away.