The Old Moon occults Pre-dawn Planets, and Missing Moonlight Enhances the Ice Giants and Orion’s Spectacular Sword!

The Moon and Planets

On Sunday afternoon, the moon reaches its Last Quarter phase, when it rises at midnight and appears half-illuminated — on its western side. For the rest of this week, the moon will be in the pre-dawn sky, leaving the night sky nice and dark for stargazing. The late rising moon will also linger to remain visible in the morning daytime sky, especially on the coming weekend.

For the second time during January, the old moon will visit Jupiter and Venus. Between about 5 am and dawn in the southeastern sky on Thursday morning, the old crescent moon will land 2.5 finger widths to the upper right of bright Venus and 5.5 finger widths to the lower left of somewhat dimmer Jupiter — making a lovely sight in binoculars and a photo opportunity. To top it off, just after 6 am local time, Saturn will rise to sit two fist diameters to the lower left of the trio.

That pretty chain of objects strung along the ecliptic should remain visible in the growing twilight until about 7 am local time. Later on Thursday, the moon’s eastward orbital motion will carry it even closer to Venus, allowing observers to find Venus in broad daylight. Folks in eastern Micronesia, Polynesia (except Hawaii), the Galapagos Islands, southern Central America, and northwestern South America will see the moon cross in front of (or occult) Venus in daylight.

Finally, on Saturday before dawn, the waning crescent moon will pass less than 3 finger widths to the lower left of Saturn. Hours earlier, centered on 19:50 GMT, skywatchers in northern and northeastern Africa, southern and central Europe, Middle East, western Asia, and parts of Southern Russia can see the moon’s orbital motion carry it in front of that planet, too!

Moon or not, those three bright planets will be in the same part of the sky all week. Jupiter will be rising after 4 am local time, Venus about 30 minutes later, and dimmer, yellowish Saturn last — at about 6:15 am local time, in a brightening sky. Saturn and Jupiter will be lowly moving farther from the sun every morning, but Venus will be descending toward the sun. Mercury is passing by the sun this week, and will join the evening sky next week.

Mars remains an ideal target for stargazers (or planet-gazers) this week. After dusk, the Red Planet will appear as a medium-bright, reddish pinpoint of light halfway up the southwestern sky. It will set at about 11:30 pm local time. Mars is slowly shrinking in size and brightness as we increase our distance from it.

Mars has been setting at about the same time all winter because it is travelling east in its orbit at about the same rate that the distant stars are migrating west due to Earth’s motion around the sun. As a result, the planet has been steadily traversing the dim water constellations. In December, Mars passed very close to distant Neptune in Aquarius (the Water-Bearer). In mid-February, Mars will pass quite close to Uranus in Pisces (the Fishes).

Speaking of those ice giants, the missing moonlight is a good reason to try and see those two dim and distant planets. Blue-green Uranus is about 1.25 finger widths above, and slightly to the left of the modestly bright star Torcular (or Omega Piscium). This week, Uranus will already be at its highest point, over the southern horizon (the best position for seeing it clearly) after dusk, then set after midnight. Dim, blue Neptune will set shortly after 8:30 pm local time, so look for it as soon as the sky is dark, while it’s higher. Neptune is sitting about three finger widths to the upper left of the modestly-bright star Hydor (Lambda Aquarii). Hydor, and a pair of stars to its east (upper left), form a sideways narrow triangle with Neptune inside of it.

Orion’s Spectacular Sword

This is a perfect week to grab the binoculars and check out Orion (the Hunter). The distinctive constellation will stand up over the southern horizon at 9 pm local time during late January evenings, and we can enjoy it until late March.

Orion’s spectacular sword is one of winter’s true astronomical treats. The sword is a few finger widths below Orion’s distinctive three-starred belt. Unaided eyes can generally detect three patches of light in Orion’s sword, but binoculars or a telescope quickly reveal that the middle object is not a star at all, but a bright knot of glowing gas and stars known as The Orion Nebula (or the Great Nebula in Orion or Messier 42, aka M42).

The Orion Nebula is one of the brightest nebulae in the entire night sky and, at 1,400 light-years from Earth, it is one of the closest star-forming nurseries to us. It’s enormous. Under a very dark sky, the nebula can be traced over an area equivalent to four full moons!

Buried in the core of the nebula is a tight clump of stars collectively designated Theta Orionis (Orionis is Latin for “of Orion”), but better known as The Trapezium, because the brightest four stars occupy the corners of a trapezoid shape. Even a small telescope should be able to pick out this four-star asterism, but good seeing conditions and a larger aperture telescope will show another two faint stars. The trapezium stars are hot young O- and B-type stars that are emitting intense amounts of ultraviolet radiation. The radiation causes the gas they are embedded in to shine brightly, by both reflecting off gas and dust as blue light and also by energizing Hydrogen gas, which is re-emitted as red light. That is why there is so much purple and pink in colour images of the nebula.

Within the nebula, astronomers have detected many young (about 100,000 years old) concentrations of collapsing gas called proplyds that should one day form future solar systems. These objects give us a glimpse into how our sun and planets formed.

Stargazers have long known about the stars in the nebula’s core, but detection of the nebulosity around them required the invention of telescopes in the early 1600’s. In the 1700’s, Charles Messier and Edmund Halley (both famous comet observers) noted the object in their growing catalogues of “fuzzy” objects. In 1880, amateur Henry Draper imaged it through an 11-inch refractor telescope, making it the first deep sky object to be photographed.

In your own small telescope, you should see the bright clump of Trapezium stars surrounded by a ghostly grey shroud, complete with bright veils and dark gaps. More photons would need to be delivered to your eye before colour would be observed, so try photographing it through your telescope or with a camera/telephoto lens on a tripod. Visually, start with low magnification and enjoy the extent of the cloud before zooming in on the tight asterism. Can you see four stars, or more? Just to the upper left of M42, you’ll find M43, a separate lobe of the nebula. It surrounds the unaided-eye star nu Orionis (ν Ori).

While you’re touring the sword, look just below the nebula for a loose group of stars, located 1300 light-years away from Earth, called Nair al Saif “the Bright One of the Sword”. This main star is a hot, bright star expected to explode in a supernova one day. It is surrounded by faint nebulosity, too. Astronomers believe that this star was gravitationally kicked out of the Trapezium cluster about 2.5 million years ago.

Sweeping down the sword and to the left (east) brings us to the star named Mizan Batil ath Thaalith (aka d Orionis) at the tip of the sword. This magnitude 4.7 star is near the limit for visibility in moonless suburban skies. About two finger widths to its right is another star of similar brightness, named Thabit, “the endurer”.

Moving upwards towards Orion’s belt, half a finger’s width (30 arc-minutes, or the moon’s diameter) above the Orion Nebula, you’ll find another clump of stars dominated by c Orionis and 45 Orionis. A larger telescope, or a long-exposure photograph, reveals a bluish patch of nebulosity around them that contains darker lanes forming the shape of a figure, called the Running Man Nebula. This is another case of gas reflecting light from the two stars mentioned.

Just above the Running Man sits a loose cluster of a few dozen stars best seen in binoculars. Then we jump higher — most of the way towards Alnitak (the eastern-most belt star), to check out a beautiful little grouping of stars collectively called Sigma (σ) Orionis. What makes this a special treat is that, in a small telescope, we find four or five stars crammed together. Check it out with your telescope — trust me, it’s pretty! It’s a bit more than a finger width to the lower right of Alnitak.

Astronomy Skylights for the week of January 27th, 2019 by Chris Vaughan.

Keep looking up, and enjoy the sky when you do. I love questions and requests — so, send me some!




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