What's In the Sky - September 2018

September nights are full of wonderful treats for amateur astronomers to enjoy with binoculars and telescopes. See some of Orion Telescopes and Binoculars' top September stargazing suggestions below:

Spiral Galaxies

The fall stargazing season kicks off in September with wonderfully placed spiral galaxies M31 in Andromeda, M33 in Triangulum, and M74 in Pisces. Use a big telescope to see these distant galaxies.

The Northern Milky Way

Early in the month, around 9 PM, the "Summer Triangle" of three bright stars, Vega, Deneb, and Altair, will be nearly overhead. In the northernmost portion of the Summer Triangle, you'll see a bright portion of the northern Milky Way. Point a telescope there, and you'll discover that the fuzzy outlines of the Milky Way will resolve into vast fields of stars to explore.

New Moon

For the best conditions to see the galaxies and clusters described above, plan a stargazing session for the night of September 9th, when the New Moon will provide dark skies. This is the best night of the month to observe the night sky since light from stars and faint deep sky objects won't have to compete with bright moonlight.

Three Globular Star Clusters

Off the western side of the constellation Pegasus, three globular star clusters almost line up in a row from north to south in September skies. These globular clusters are, from north to south, M15 in Pegasus, M2 in Aquarius, and M30 in Capricorn. From a dark sky site, you can easily find all of them in 50mm or larger binoculars.

Planetary Nebulas in the Summer Triangle

Use a star chart and see how many of these planetary nebulae you can find in September: the famous Ring Nebula (M57) in the constellation Lyra; the Dumbbell Nebula (M27) in Vulpecula; and the "Blinking Planetary," NGC 6826 in Cygnus. Not far outside the western boundary of the Summer Triangle is a small but intensely colorful planetary nebula, NGC 6572. All these can be seen in a 6" or larger telescope. Enhance your views of these distant clouds of dust and gas with an Oxygen-III filter.

The Great Andromeda Galaxy (M31) - Imaged by Insight Observatory on ATEO-1

The Galaxy Next Door

In early September, lurking low in the northeast sky is another galaxy, separate from our Milky Way - the Great Andromeda Galaxy (M31). From a very dark area without a lot of light pollution, the core of M31 is visible with the unaided eye as a slightly fuzzy spot in the sky. A pair of 7x50, 9x63 or larger binoculars will give you a much better view, and any telescope will help reveal some of the neighboring galaxy's subtle dust lanes.

Dip into the Whirlpool

If you haven't tracked down "The Whirlpool Galaxy," M51, just off the handle of the easily recognizable Big Dipper asterism, do it now while you still can! It will be too low for most to get a good view after September, and you'll need to wait until late winter or next spring to catch a good view of this truly picturesque galaxy. An 8" or larger telescope will help you see the faint details of M51 more clearly.

A Brilliant Open Star Cluster

Off the western end of the constellation Cassiopeia is the beautiful Open Star Cluster M52. You can find it with 50mm or larger binoculars from a dark sky site, but the view is definitely better in a telescope. With an 8" or larger scope, and with the aid of an Orion UltraBlock or Oxygen-III eyepiece filter, you may even be able to catch views of faint nebulosity surrounding M52.

Don't Miss the Double Cluster

If you enjoyed observing M52, you'll love the popular favorite "Double Cluster in Perseus." Lying between constellations Cassiopeia and Perseus is a bright, fuzzy spot in the Milky Way, and a binocular will reveal two bright open star clusters close to one another. For a real treat, use a telescope equipped with a wide-angle eyepiece to explore these sparkling clusters. In early September, the "Double Cluster" appears low in northeastern skies around 9 PM, but it becomes a real showpiece later in the evening as it climbs higher in the sky.

Planetary Viewing

Viewing planets is always rewarding, and September will provide ample opportunities. Mars and Saturn are still visible until late in the night (early in the morning). Jupiter is still up in the early evenings but will set fairly soon after dark. Go out and enjoy!

A Thinly Veiled Challenge

A challenging object to see in September is the supernova remnant called the Veil Nebula, located in the constellation Cygnus, which is nearly overhead as soon as it gets dark. With the help of a star chart, aim your telescope at the naked-eye star 52 Cygni. One branch of the Veil crosses over this star, and to the east are brighter segments of this roughly circular nebula. While the Veil Nebula can be seen in big binoculars by expert observers under very dark skies, you will likely need at least a 6" aperture telescope and an Orion Oxygen-III eyepiece filter if you are anywhere near city lights.

All objects described above can easily be seen with the suggested equipment from a dark sky site, a viewing location some distance away from city lights where light pollution and bright moonlight does not overpower the stars.

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The Solar System In a Night-Shell

Recently, you may have noticed an extra one or two very bright stars in the sky, just after sunset. That’s because we’re currently experiencing a rather special celestial treat: a relatively rare positioning of all eight planets (and, three minor planets!) into just a bit more than one side of the sky - at nearly the same time! Alignments like this aren’t exactly common, so, go outside and take a look - while it’s still not too late! (This celestial configuration will begin to deteriorate over the coming weeks).

Starting at sunset, in their order of appearance, relative to their apparent distance from the sun, and just to the west of the sun, is Mercury, the first planet out from the sun, which is now so close to our star, from our perspective, that it’s easily lost in the glare and a bit hard on the eyes for that reason, without a telescope, but it’s there -  just about 6 degrees to the southwest, at stellar magnitude +.60.**

Believe it or not, next up - we’re already at the outer reaches of the Solar system - minor, or dwarf planet, Pluto! But that’s because of its position against the sky, in the relative background, as compared to the other, and much closer planets. For now - just know that it’s there, about 15 degrees to the east of Saturn. It bottoms out at a dim +14.4 magnitude, accessible only in a moderate to large-sized telescope.

Next, moving, now, East of the sun is a dwarf planet, Ceres. You’ll need a small telescope to spot it. Ceres was discovered, telescopically, in 1801, and at that time, it was realized that Ceres was much closer to Earth than were the stars - but smaller than any planet; therefore, it was cataloged as an asteroid. And, it kept that label, until relatively recent years when it was re-labeled a minor planet. Under that heading is the sub-heading of, ‘dwarf planet’, and that’s where Ceres currently resides, "taxonomically", anyway. The reasons for the changes to Ceres, 4 Vesta, and Pluto as dwarf planets are entirely logical and valid; you’ll have to take my word for that. You’ll find Ceres if you dare - and, if you have a medium-sized telescope - between the sun and Venus, at a dim, +8.8 magnitude.

Now, on our way to Venus. Venus, the second planet from the sun - is the brightest thing in the sky (sans the moon and sun). Seemingly hanging there, low in the west, Venus shines its stunning, white brilliance down on us - at a staggering magnitude -4.4, and at about 12 degrees east of the sun. If you miss it - well, you’re just not paying attention!

Now - look down at the ground by your feet. There sits Earth, the third planet from the sun. If you were to see yourself standing there, from the perspective of the orbiting, International Space Station, you’d first note that you were standing, nearby some dividing line - the line delineating light from the darkness: the terminator, dividing night from day. You are just about, literally, to enter and cross into, the "Twilight Zone"! (Now, how many people can say that they’ve, knowingly, done that - hmmm?!) And this is a good thing because it represents the progression of time, and the rotation of Earth on its axis and, thereby, rolling you - or, perhaps, dragging you - into the deep, dark night. But this is an even better thing because the passage of the early evening hours will bring, up into the sky, from over the eastern horizon, three of our Solar system's showpieces; Jupiter, Saturn, and Mars.

First, sitting, watchfully - almost “king-like” - and due South, at an elevation of around 30 degrees, is His Deified Majesty, Jove - also known by the Romans, as Jupiter. With just about any pair of binoculars, you’ll get to see four of, giant Jupiter’s, giant moons - Callisto, Europa, Ganymede, and Io - that is, unless one or two of them happen to be in Jupiter’s shadow at the time of your observation. But don’t worry; they don’t stay in the shadow behind the planet long! With a telescope, you may also see some, very pastel, cloud bands, near the planet’s equatorial region. Jupiter is now, the third brightest light, in the sky, at a bright, white-ish, magnitude of -2.70.

Have you ever seen ‘rings’ around any celestial object before?; I mean, for yourself - with your very own eyes?! Probably, you haven’t - so now’s your chance! - that is if you happen to have access to, at least, a small telescope, or high-powered binoculars.

If not, don’t worry about it; you still cannot help but notice Saturn, anyway, because it’s now such a  bright, yellowish-white, at an apparent magnitude of +.70: one of the very brightest lights currently in the sky, best seen around 9:00PM. But in a telescope, you will make out Saturn’s ring system, currently lying at an oblique angle to its plane of rotation, so that they will appear to be, almost, “wide-open” at this time around the planet - and that is a wonderful, and rare thing, indeed; Saturn’s rings go through long cycles of appearing open or closed, from our perspective, about every 27 years! Right now they are “wide-open” - you may never get to see this, again…

After Saturn is another object out there, just worth noting, and going unseen without a telescope: dwarf planet, and former asteroid, 4 Vesta. Its feeble light, just creeps through our atmosphere at a dismal +6.4 magnitude, well beyond the abilities of the average, human eye.

Now, comes Mars. Make sure you identify this small-ish, ruddy world for long-term memory: Mars is closer to Earth than it has been in 157 years! Though the red planet closes in on Earth every two years, due to the proximity of the orbits of both planets, there is another component to the Martian orbits’, slightly elongated shape which brings it even closer, periodically. This happens when the point in its orbit that lies closest to the sun, is in sync with the Earth’s position - and that is right about now!

Mars is currently experiencing one of the relatively rare, long-duration, global sandstorms that it's known for. The raging storm has been going on, for about 3 months now. I saw Mars through the telescope about two weeks ago, at high magnification. Though the planet, normally, has a variety of surface features to offer the observer, in the form of dark grey patches, volcanic calderas, white polar caps, and such, it now presents a uniform, planet-wide rust color, as atmospheric particulates from the dust storm circulate around its small, thin blanket of air. However - Mars is the second brightest thing in the sky, right now, after Venus - looking more like a reddish "blob", hanging in the air, toward the South than it does a star or a planet. There is a distinct perception of a disk to this orb, due to its slightly larger angular size in the sky than that of the other planets and, due to its current proximity to Earth. Mars is now glowing, distinctly reddish, at magnitude -2.6, rising at around 8:30PM and well placed for viewing, high up in the sky, by 11:00PM. It’s worth the view, with or without a telescope or binoculars!

And, nearly last, but not, nearly least - by any stretch - are Uranus and Neptune - the seventh and eighth planets of our Solar system - far beyond the reach of the unaided eye, but within telescopic range. They are nearby each other, well into the small hours, at around 30 degrees and 60 degrees, east, of Mars, and +5.7 and +7.8 magnitudes, respectively.

This leaves our own, familiar moon, Luna, now (at the time of this writing), as a dainty, waxing crescent, sitting just above Venus, but moving progressively toward the east, as the nights of the month wear on. And, there you have It - our entire Solar system, in a “night”-shell (well, you just know I couldn’t resist that one!)

** The system used by astronomers to denote the relative, apparent brightnesses in celestial objects, is the Stellar Magnitude Scale. Beginning at 0, the scale uses both positive and negative numbers: those in the minus range, are brighter than those in the plus range. Though it's called the ‘stellar’ magnitude scale, it is used to mark the brightnesses of all celestial objects; stars, planets, comets, and asteroids included. On that note, the consistently, brightest point of light that can be seen from the Earth, is the star, Sirius, in the constellation Canis Major (the 'Big Dog'). It is given the negative magnitude number, -1.4. The planet Venus, currently, is at magnitude -4.3 - several times brighter than Sirius - but Venus’ albedo varies over time, and,  although Venus is the brightest object in the sky, after the sun and moon - it is a planet.  On the plus side of the scale, the human eye can see stars down to about, a fairly dim, magnitude +6, on a very dark, clear night. And so, the answer to the oft-asked question: “What is the brightest star in the night sky?”, is, technically, the star Sirius, at magnitude -1.4.

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2018 Mars Opposition

Like all the planets in our solar system, Earth and Mars orbit the sun. But Earth is closer to the sun and therefore races along its orbit more quickly. Earth makes two trips around the sun in about the same amount of time that Mars takes to make one trip. So sometimes the two planets are on opposite sides of the sun, very far apart, and other times, Earth catches up with its neighbor and passes relatively close to it.

During opposition, Mars and the sun are on directly opposite sides of Earth. From our perspective on our spinning world, Mars rises in the east just as the sun sets in the west. Then, after staying up in the sky the entire night, Mars sets in the west just as the sun rises in the east. Since Mars and the Sun appear on opposite sides of the sky, we say that Mars is in "opposition." If Earth and Mars followed perfectly circular orbits, the opposition would be as close as the two planets could get.

Artist's concept of Mars Opposition on December 24, 2007. The distances between the sun, the planets, and the distant nebula are not to scale. Image credit: NASA.

Of course, nothing about motion in space is quite that simple! Our orbits are actually elliptical (oval-shaped), and we travel a little closer to the sun at one end of our orbits than at the other end.

Mars oppositions happen about every 26 months. Every 15 or 17 years, opposition occurs within a few weeks of Mars' perihelion (the point in its orbit when it is closest to the sun). This year, Mars opposition occurs on July 27, 2018.

An opposition can occur anywhere along Mars' orbit. When it happens while the red planet is closest to the sun (called "perihelic opposition"), Mars is particularly close to Earth. If Earth and Mars both had perfectly stable orbits, then each perihelic opposition would bring the two planets as close as they could be. That's almost the way it is.

NASA's Hubble Space Telescope captured this striking image of Mars during the 2016 opposition and an illustration of the relative 'tilt' in the orbits of Earth and Mars. Image credits: NASA.

But once again, nature throws in a few complications. Gravitational tugging by the other planets constantly changes the shape of our orbits a little bit. Giant Jupiter especially influences the orbit of Mars. Also, the orbits of Earth and Mars don't lie in quite the same plane. The paths the planets take around the sun are slightly tilted with respect to each other.

So, with all these added factors, some perihelic oppositions bring us closer together than others. The 2003 opposition was the closest approach in almost 60,000 years!

Mars's orbit is more elliptical than Earth's, so the difference between perihelion and aphelion is greater. Over the past centuries, Mars' orbit has been getting more and more elongated, carrying the planet even nearer to the sun at perihelion and even farther away at aphelion. So future perihelic oppositions will bring Earth and Mars even closer. But we'll still have bragging rights for a while. Our 2003 record will stand until August 28, 2287!

Article Source: Mars in Our Night Sky - Mars Opposition

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