August Night Sky
Sky events for this month & objects for observation and can be found here.
A larger printable version of this chart can be found here.
As can be seen on this months chart for August, there is a parade of planets visible in the evening southern sky. Venus will be visible shining brightly just after sunset in the west, but sets by the time full darkness occurs at about 10:30 pm. Jupiter, Saturn with its beautiful rings, and Mars are all in view for most of the evening hours, and Mars is particularly bright as it makes a close "perihelion" (close to the Sun) approach in its highly elliptical orbit:
The biennial close approaches between Mars and Earth are not all the same. Mars’ orbit around the Sun is highly elliptical; the proximity to Earth can range from 56 million kilometers (35 million miles) to 101 million kilometers (63 million miles). In the diagram above the distances between the Earth and Mars for different oppositions are listed in "astronomical units" - with 1 au being the average distance of the Earth to the Sun - 150 million kilometers (93 million miles). Oppositions occur because about every two years Earth’s orbit catches up to Mars’ orbit, aligning the Sun, Earth, and Mars in a straight line, so that Mars and the Sun are on "opposing" sides of Earth. This phenomenon is a result of the difference in orbital periods around the Sun between Earth’s closer orbit and Mars’ farther away orbit.
While a bright and beautiful amber diamond in the sky, unfortunately for telescopic observers, perihelion oppositions of Mars are low in the sky for northern hemisphere observers, and the Earth's sometimes turbulent atmosphere can often impair viewing of significant detail. Additionally, a large dust storm which began in June has engulfed the planet, which while it has made the planet even brighter in the sky, has also made the subtle shadings of the surface (greatly enhanced in the images below) more difficult to observe:
If past planet-wide dust storms are any indication, the current dust storm will last at least a couple of months. As you observe Mars in the sky in the weeks ahead, remember how much data and information scientists are gathering to better understand the mysterious weather of the Red Planet. While it is a bit disappointing for telescopic observers, the spacecraft orbiting Mars and the landers exploring the surface are gathering a tremendous amount of data that could aid in future explorations and result in discoveries about how the mysterious weather of Mars takes place.
Visible all this month, and peaking on the evening of August 12-13, is the venerable Perseid meteor shower, resulting from the dusty debris of comet Swift-Tuttle which orbits the Sun every 133 years, and passes very near to the Earth. Click the image below for a 3D graphical representation of the Perseids:
Meteors - mostly small grains of dust and rock which enter the atmosphere at speeds ranging from 11 km/sec (25,000 mph), to 72 km/sec (160,000 mph) and burn up in our atmosphere - can occur at any time on any night and appear in any part of the sky. On a dark, moonless night you might see a half dozen of these sporadic (random) meteors per hour. However, whenever Earth encounters a stream of gritty debris left in space by a passing comet, the result is a meteor shower.
The Perseid meteor shower can deliver at least one meteor per minute under pleasant summer skies. But the shower's peak performance is relatively brief, so timing is important. Fortunately, the midpoint of this range falls during the night of August 12-13 for North America. Moreover, the Moon will be new, so observing conditions are about perfect! Like all meteor showers, it's best seen after midnight, but can be seen any time after twilight ends on the evening of the 12th and the radiant (near the Double Cluster in Perseus) clears the northeast horizon. You might be rewarded with bright firefalls that skim Earth's atmosphere and create long, dramatic streaks in the sky.
1. In the evening hours you won’t see as many meteors, but you still might catch an “Earthgrazer,” which is a slow-moving and relatively long-lasting meteor that travels horizontally across the sky. If you see one, you’ll have a new appreciation for evening meteor-watching.
2. After midnight, the part of Earth you’re standing on has turned into the meteor stream, which means the radiant point for the shower will be above your horizon. After the radiant rises, more meteors are flying … and for 2018, in a moonless sky.
3. Make yourself comfortable. Sprawl out upon a reclining lawn chair, with an open view of sky. Bring along a blanket or sleeping bag. Your eyes can take as long as 20 minutes to adapt to the dark, so give yourself at least an hour of observation time.
4. Avoid city lights. This goes without saying, but just a reminder. A wide open area – a field or a lonely country road – is best if you’re serious about watching meteors.
5. Watch with friend or friends, and try facing in different directions so that if someone sees a meteor, that person can call out – “meteor!” – to the rest.
6. Notice the speed and colors of the meteors. The Perseids are known to be colorful! The Perseids are swift-moving, entering Earth’s atmosphere at about 60 km (35 miles) per second.
7. Watch for meteor trains. A meteor train is a persistent glow in the air, left by some meteors after they have faded from view. Trains are caused by luminous ionized matter left in the wake of this incoming space debris. Bright Perseids are known to leave persistent trains. They linger for a moment or two after the meteor has gone.
8. Embrace the night. Most people bubble with excitement about seeing meteors in all sorts of conditions – moon or no moon – city lights or no city lights. The Perseids, in particular, tend to have a lot of fireballs. So camp out and make a night of it!
9. Enjoy the shower as much as possible this year, as the next good opportunity will not occur until 2021 due to the phase and brightness of the Moon.