July New Moon 2018: See Mercury at Its Best in the ‘Moonless’ Sky | Innovation Tech
The new moon arrives on Thursday (July 12), and within a day, Mercury will be at its best for evening observers this summer — the waxing crescent moon will swing by the planet on July 14.
The moon is officially new at 10:48 p.m. EDT on July 12 (0248 GMT on July 13). A new moon occurs when the moon is between the sun and Earth. Technically, both objects are in conjunction, meaning they are on the same north-south line that passes through the celestial pole, near the star Polaris. (The term “conjunction” is usually applied to other celestial bodies, such as planets).
Because the new moon is between Earth and the sun, it isn’t visible unless there is a solar eclipse — that is, when the moon passes in front of the sun when viewed from Earth. 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, which means that it doesn’t always pass exactly between the sun and Earth, and the moon’s shadow “misses” Earth. July’s new moon happens to coincide with a partial solar eclipse, which will occur for observers in southern Australia and part of Antarctica. [Infographic: Earth’s Moon Phases, Monthly Lunar Cycles]
The new moon rises and sets at nearly at the same time as the sun. For viewers in the northeastern U.S., the new moon will rise at 5 a.m. local time in New York on July 12 and set at 8:08 p.m., while the sun will rise at 5:35 a.m. and set at 8:27 p.m., according to timeanddate.com. On the night of July 14, the moon will rise at 7:18 a.m. and set at 9:53 p.m. for viewers in New York. It will be a very thin crescent, most easily visible in the evening.
Conjunction of the moon and Mercury
Observers must take care when looking for objects so close to the sun so as not to damage their eyes, but once the sun sets, the crescent moon will make for some beautiful vistas. On the night of the new moon, Mercury will be visible in the evening, setting at 9:43 p.m. in New York. At about 9 p.m., it will be 8 degrees above the horizon. On July 14 at 6:04 p.m. EDT (2204 GMT), the moon will pass about 2 degrees north of Mercury, the “elusive” planet, which is often difficult to see because of its proximity to the sun. At this time, the moon will be in conjunction with Mercury, as the two objects will share the same right ascension, or celestial longitude. Observers in the eastern U.S. won’t be able to see the moment of conjunction because the sun will still be up, but after the sun sets at about 8:30 p.m., the moon and Mercury should become visible with a very flat horizon and a clear sky — the planet will be about 2 degrees, or four lunar diameters, above the western horizon.
Mercury is relatively bright, but until the sun gets at least a few degrees below the horizon, it won’t be visible. Generally, the brightest stars come out once the sun gets at least 6 degrees below the horizon, which is the end of civil twilight and the beginning of nautical twilight (which lasts until the sun gets 12 degrees below the horizon). On July 14, civil twilight will end at about 8:58 p.m. in New York, so at that point, one should start to see brighter stars, as well as some planets such as Venus (the third-brightest object in the sky after the sun and the moon).
According to heavens-above.com calculations, Mercury will be at magnitude 0.7, so it will be only a bit less bright than bright stars such as Vega (magnitude 0.0). (Lower magnitudes are brighter.) However, it will be only about 7.3 degrees above the horizon on July 14 at 9 p.m. in New York, or slightly less than the width of a closed fist. To spot it, one can use the moon, which by that time will be a about a degree (approximately two lunar diameters) east of the planet’s position. If you can spot the crescent and draw an imaginary line toward the sun, you should be able to see Mercury.
July 12 also happens to be the day that Mercury reaches its greatest eastern elongation, or its greatest angular distance east of the sun. The planet will be 26 degrees away from the sun — making it much easier to see, as it will linger in the sky longer after sunset. Mercury won’t get very far above the horizon for Northern Hemisphere observers because the plane of the ecliptic, where the planets roam, is tilted at an angle to the horizon as seen from Earth. In the summer months, that angle tends to be shallower for Northern Hemisphere skywatchers. So spotting Mercury, even with its relatively favorable position, will still be a challenge.
Although it is hard for Northern Hemisphere observers to see Mercury, those in the Southern Hemisphere might have an easier time. The moon will become officially new for eastern Australians at 12:48 p.m. local time on July 13. The sun will set at about 5 p.m. — earlier than in the Northern Hemisphere, since July is the middle of the austral winter. Nautical twilight will end at about 6 p.m., meaning the sky is just getting dark enough to see a few stars. The early sunset means Mercury is a few degrees higher above the western horizon than it will be from New York — about 12 degrees. That’s still a bit low, but it allows for more time for the sky to get dark enough for observers to see Mercury before the planet dips beneath the horizon at about 7:06 p.m. local time.
See Venus, the “evening star”
Mercury isn’t the only planet we will see in the evening sky. Venus continues its run as an evening star in July. The new crescent moon will pass Venus on July 15, a day after it passes Mercury. The moon and Venus will reach conjunction at 11:32 p.m. EDT (0332 GMT on July 16). For viewers in New York, the planet will have set already.
However, if you live in California, Washington state or Oregon, Venus will still be well above the horizon when the waxing crescent moon passes by. The moon will pass about 1.6 degrees north (about three lunar diameters) of the planet. For skywatchers in Los Angeles, Venus will be 22 degrees above the horizon when the conjunction occurs about a half-hour after sunset, though the sky will still be relatively bright, making the planet challenging to see. [Skywatcher Photos: Dazzling Views of Venus & the Moon]
More planets on parade
Planets farther from the sun than Earth is will also make an appearance on the night of the new moon. On the night of July 12, when the moon becomes officially new, Marswill rise at 9:48 p.m. for observers in New York City. Mars will be in Capricornus, a relatively faint constellation, so the Red Planet will be distinct from city locations.
Jupiter will be in the western half of the sky; it sets at 1:23 a.m. on July 13, according to heavens-above.com calculations. But it will be well-placed for skygazers in the city, as the planet’s whitish-yellow glow will be bright enough to be seen even in light-polluted areas. Jupiter is in Libra, which has no first-magnitude stars, so like Mars, the planet will be relatively obvious.
Saturn, meanwhile, will rise at 7:16 p.m. in New York City on July 12 and will set at 4:27 a.m. the next morning. Therefore, it will be visible all night, and the rings will be visible through even a modest telescope or a large pair of binoculars. The ringed planet is low in the sky for Northern Hemisphere observers, as it is in Sagittarius. Saturn will reach the highest point for midnorthern latitudes at 11:47 p.m. local time in New York City and will be only about 26 degrees above the horizon then. (To find when Saturn is highest in your time zone, check the time difference from New York; West Coast observers will see it get there at about 8:47 p.m., while people in London will see it happen at 4:47 a.m.).
Antipodean skywatchers will get a much better view, since during the winter months, the ecliptic is at a much steeper angle relative to the horizon from places like Australia or New Zealand. Saturn will also be as high as 79 degrees above the horizon — nearly straight up. Jupiter will be about 71 degrees high at 7:19 p.m. local time, and the sun will have already set. Mars will have an altitude of 81 degrees. Objects higher in the sky are often easier to see than those close to the horizon.
Editor’s note: If you have an amazing night-sky photo you’d like to share with us and our news partners for a possible story or image gallery, please contact managing editor Tariq Malik at [email protected]
You can follow Space.com on Twitter& @Spacedotcom. We’re also on Facebook and Google+. Original article on Space.com.