In January, the moon will make a close approach to several planets both before and after it enters its new phase on Jan. 24, offering some fine photo opportunities in a bright winter sky.
The new moon will occur on Friday (Jan. 24) at 4:42 p.m. EST (2142 GMT), according to NASA's SkyCal site. On Jan. 22, the waning crescent moon will make a close pass to Jupiter in the predawn sky, and on Jan. 28 the moon, just 4 days old in the evening sky, will swing by Venus and Neptune.
The new moon is when the moon is directly between the sun and Earth, which occurs about once every 29.5 days. The moon's orbit isn't perfectly lined up with Earth's, so even though the moon is between our planet and its star it doesn't block its light and create a lunar eclipse every month, as it did in December. Technically, the new moon is when the moon shares the same celestial longitude as the sun, also known as a conjunction. (The term conjunction applies to any two celestial bodies at the same celestial longitude).
The conjunction with Jupiter on Jan. 22 will involve a 28-day-old moon, which will be a thin crescent that rises before sunrise. The conjunction itself won't be visible from the United States, though the planet and the moon will still be close together in the sky.
The moon will rise at 6:25 a.m. local time on Jan. 23 in New York City, while the conjunction itself occurs at 9:42 p.m. on Jan. 22. By the time the sun rises at 7:13 a.m. on Jan. 23, the moon will be only 6.5 degrees above the horizon. However it will be surrounded by Jupiter on one side, which will be 10 degrees in altitude, and Saturn on the other, which will be about 4 degrees up, according to heavens-above.com calculations.
To catch the conjunction itself, you need to be in a place where the moon rises before 9:42 p.m. EST (0242 GMT) — the moment of conjunction — which means being east of Greenwich, England. One must also move south, so that the ecliptic (the plane of the planetary and lunar orbits projected onto the sky) is at a steeper angle to the horizon, putting the moon and Jupiter a bit higher up.
In Dubai, for example, the conjunction will occur at 6:42 a.m. local time, about 20 minutes before sunrise. The moon will pass within 21 arcminutes — just over two-thirds of a lunar diameter — of Jupiter, according to skywatching site in-the-sky.org. The two will be about 12 degrees above by dawn, which is at about 6:49 a.m. local time on Jan. 23.
Farther north catching the conjunction becomes more difficult. As one moves north the pair are closer to the horizon. For Southern Hemisphere skywatchers the situation is slightly better — from Sydney, Australia the conjunction will be during the day, at 1:41 p.m. local time Jan. 23, but the moon and Jupiter will be a bit higher, 18 degrees above the horizon by the time the sun rises at about 6:06 a.m. local time.
On the night of the new moon, for midnorthern latitudes, the outer planets will not be evident until just before sunrise. For example, in New York City, at 5 a.m. local time, the sky is still quite dark — sunrise isn't until 7:13 a.m. per timeanddate.com, and astronomical twilight (when the sun is no more than 18 degrees below the horizon) doesn't begin until 5:37 a.m. But only Mars will be up; it will be about 10 degrees above the southeastern horizon. On that morning Mars will rise at 3:57 a.m. local time. Jupiter will rise later, at 5:59 a.m. and Saturn, at 6:44 a.m., making catching planets difficult as the sky will be brighter by the time they peek above the horizon.
On the evening of Jan. 23, after sunset, Venus will be in the southwestern sky for observers in the northern hemisphere; its relative altitude will depend on how close to the equator one is. Earth's sister planet will still be a bright presence, shining at magnitude -4.0, making it the brightest object in the sky. In New York City, the planet will be about 30 degrees above the horizon at 5:10 p.m. local time — the sun sets at 5:02 p.m. At that point, it won't be quite dark yet, but Venus is bright enough that keen-eyed observers might catch it. The planet will set in New York at 8:12 p.m.
In San Juan, Puerto Rico, the sun will set later on Jan. 23 — 6:13 p.m. local time — but Venus is still quite high, a good 37 degrees. Venus will set at 8:58 p.m.
Mercury is also in the evening sky, though from New York City (and locations at similar latitudes such as Chicago) the planet is only about 5 degrees above the horizon at sunset. Not being as bright as Venus it will be harder to catch. As one moves south the situation improves; in San Juan the planet is at 7.3 degrees at sunset on Jan. 23. But count yourself lucky if you manage to see it.
If one has a telescope, a conjunction of Venus and Neptune will occur on Jan. 27. Venus will pass just 4 arcminutes south of Neptune. Visible in the evening sky just after sunset in the constellation Aquarius, the two planets will be close enough that a pair of binoculars or small telescope will show them together in the same field of view.
Neptune, though, is never visible with the naked eye — it is too faint at magnitude 7.9 (even people with excellent vision and a completely dark sky can't see anything dimmer than magnitude 6.5 or so). The actual conjunction occurs at 4:21 p.m. EST (2121 GMT). For skywatchers in the U.S., the conjunction occurs before sunset, which happens at 5:06 p.m. local time in New York City.
On Jan. 28, the now waxing crescent moon will make a close approach to Venus, passing about 4 degrees away. From New York City by about 5:30 local time, the pair will be in the southwestern sky, with the moon just to the east of Venus.
January's skies are winter skies in the Northern Hemisphere, which means that some of the brighter constellations are prominent. By about 6:30 p.m. local time, the constellations of Orion, Taurus and Gemini are all above the eastern horizon and so is most of the constellation Canis Major, which contains Sirius, the brightest star in the Northern Hemisphere sky. Orion also hosts the star Betelgeuse, which marks the hunter's left shoulder (as seen from the ground). Betelgeuse has made headlines recently among astronomers because it has noticeably dimmed, though it is still unclear why.
By about midnight on Jan. 23, the constellation Leo will be in the high eastern sky, with Orion just past the meridian. Taurus is above and to the left; its brightest star Aldebaran also marks the location of the open star cluster called the Hyades, which marks the bull's head. Also visible is Canis Minor, which can be found by drawing a line between Orion's shoulders and tracing it to the left (eastwards). Canis Minor, otherwise known as the Little Dog, contains the star Procyon, which is not only bright but a near neighbor to the sun, only 11.5 light-years away.
On the southern horizon to the east of Canis Major, skywatchers in the Northern Hemisphere can see Puppis, one of the three constellations that make up the ship, often connected with the famous Argo that Jason sailed. To see the rest of it, one has to go south, to the tropics or the Southern Hemisphere.
Those Southern Hemisphere residents will see Vela and Carina, the two other components of the ship, as well as Puppis. In Buenos Aires, the new moon will occur at 6:42 p.m. local time on Jan. 23, and the sun will set at 8:06 p.m. By midnight, Vela and Carina are both near the zenith, and the Southern Cross is just to the east of the meridian.
Editor's Note: If you snap an amazing night sky picture and would like to share it with Space.com's readers, send your photos, comments, and your name and location to email@example.com.
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