Skywatch August 2016

Skywatch August 2016

August 2016 features a gathering of planets just above the sun at dusk, and the return of the most famous meteor shower. There is a chance to catch all five naked-eye planets at the same time in the early evening, and Venus and Jupiter have their closest gathering since the year 2000 at the end of the month.

Planets in August

Planetary pile-up in the evening sky

In mid-July it became possible to see all five naked-eye planets in the early evening sky; that phenomenon continues through August. The situation is divided into two groups: the planets Jupiter, Venus and Mercury hanging low in the west at dusk, and Saturn and Mars shining in the south. That said, since the western planets set by 8 p.m., you’ll have only about 30 minutes, from 7:30 to 8:00 p.m., to collect the full set of planets.

Venus, Jupiter and Mercury together at dusk

The two brightest planets, Venus and Jupiter, gather low in the west with Mercury at dusk throughout August. To see this gathering in early August, look west between 7:15 and 8:00 p.m. Venus shines brilliantly in the west, at minus 3.88 magnitude; by the time you pick it out, around 7:15 p.m., it will be only about ten degrees above the west horizon, or the width of your hand at arm’s length. Venus sets by 8 p.m.

Early in the month, draw a line from Venus up to Jupiter, the second brightest dot in the sky. As it gets dark, look for Jupiter about two hand-widths above Venus, shining at minus 1.75 magnitude. Jupiter sets around 9:15 p.m. in early August, well over an hour after Venus.

If you draw a line from Venus to Jupiter in the first week of August, the planet Mercury will be in between the two brighter planets. Mercury shines at around zero magnitude, as bright as a very bright star. It appears closer to Venus than Jupiter at the start of the month, and almost exactly in between the other two planets by the 7th.

Of particular note: look for the very, very slender crescent moon low in the west on August 4; it will be just to the left of Mercury that night. The following night, August 5, the moon will be just to the left of Jupiter.

From August 8 through 23, the three planets will, night by night, appear to change from a line into a triangle. Venus will continue to appear about 7:15 p.m. every night, and will remain about 10 degrees above the horizon at first darkness through the month. However, every night Jupiter will appear a little lower and a little closer to Venus at dusk; meanwhile, Mercury will appear more and more to the left of a line drawn between Venus and Jupiter.  By August 21, the three planets will make a very striking triangle: Venus on the bottom, Jupiter five degrees above Jupiter, and Mercury about six degrees (three fingers) to the left of Venus.  The whole tight triangle should be visible by 7:30 p.m., very low in the west, and sets at 8 p.m.  By August 23, the three planets make a very compact, almost equilateral triangle.

From then to the end to the month, Venus seems to get closer and closer to Jupiter; on the night of August 27 the two planets are side by side in a very tight gathering, less than 1/4th of a degree (half the width of the moon) apart. This will be the tightest gathering of the two brightest planets since the year 2000; it may appear that they are practically fused into a single light!  On this night, as throughout the month, you only have about 45 minutes to catch this lovely sight, from dusk till the planets set together at 8 p.m.  Make sure you have a clear, flat horizon to view this close gathering.

After this close gathering on the 27th, Venus will appear above Jupiter throughout the final days of August, as Mercury fades in brightness to the lower left of the two brighter planets. By the last day of the month, we’ve lost Mercury, and the triangle will be gone as Venus and Jupiter shine together in the western skies at dusk.

Mars, Saturn and Antares: the triangle continues

The other two naked-eye planets, Saturn and Mars, are also visible in the evening sky this month. As it get dark in early August, look due south; Mars is the orange dot to the right of the orange star Antares, the brightest star in the constellation of the Scorpion. Saturn is directly above Antares; the two stars and the planet form a compact triangle at the start of August.

As the month goes on, Mars will appear closer each night to a line drawn from Antares to Saturn; due to this, what was a nice triangle on August 1 will squish itself into a straight line running from Antares to Mars to Saturn by August 23. (This is the configuration of Antares, Mars and Saturn you see on our August sky map, with a straight line between the orange star Antares, the orange planet Mars, and Saturn.)

From August 24 to the end of the month, Mars will appear a little more to the left of Antares and Saturn night by night; by the end of the month, there anothernice triangle between the three dots of light, now with Mars on the left side of the triangle.

In early August, Mars sets by 1 a.m. and Saturn sets by 1:45 a.m. By the end of the month the two planets set together, at midnight.

Saturn keeps its brightness through the month, fading just slightly from 0.34 to 0.48 magnitude between the first and last of the month. While Mars remains brighter than Saturn, Mars’ brightness drops considerably as the month goes on, from minus 0.75 at the start of August to minus 0.28 at the end.

Look for the moon, around first quarter, next to Mars and Saturn on the nights of August 10 and 11.

Other sky events in August

Perseid Meteor Show

The Perseids are the most famous meteor shower of the year, with up to 80 per hour. The peak of the shower occurs early in the morning on August 12, from 12:01 am till dawn; and again early in the morning of August 13, 12:01 a.m. till dawn. The moon should not be too much of a problem this year; the moon is waxing gibbous during this shower’s peak, setting by 1 a.m. on August 12 and before 2 a.m. on August 13. So, the moon gets out of the way right as the shower starts picking up.

To view shooting star showers, just find a dark location (as little city light as possible) and get comfortable (a lawn chair is a good idea). While many meteors seem to be coming from the constellation of Perseus, which rises in the east around midnight, check the entire sky out for streaks of light.

As with all meteor showers, the viewing of the Perseids will be better after midnight. These repeating annual events are caused as the earth enters into debris left over from a specific comet; in this case, Comet 109 P Swift Tuttle. As the earth goes around the sun, our planet runs into the same debris at the same time each year. This is why these showers occur at the same time each year. After midnight, the part of the earth that you are on is facing toward the debris that causes the meteor shower.  With the Perseids, this comet debris is located in the direction of the constellation of Perseus the hero; because the streaks of light seem to come from that part of the sky, the shower is called the Perseids shower.

August star map

Like all of our monthly maps, this one is good for 10 p.m. on the first day of the month, 9 p.m. for the middle of the month, and for 8 p.m. at the end.

The Scorpion (“Maui’s Fishhook” in the Hawaiian Islands) is prominent in the south on the map, and is visited by both Mars and Saturn.

The summer triangle – three stars pulled from three different constellations – approaches the very top of the sky, with the brightest of the three, Vega, nearly overhead.

The Big Dipper is getting quite low in the north by August, and in fact will set only about an hour after map-time. The Big Dipper points to the North Star and is on exactly the other side of the North Star from Cassiopeia; usually at our low latitude in the Hawaiian Islands we see either the Big Dipper or Cassiopeia, but not both.  Here in August, at map-time, you can see both famous constellations at the same time.

Among the constellations missing from the map are the Southern Cross, which is visible in the islands only from December through June; and Orion, which comes up in August just before daybreak.

Moon phases (Hawaiian Time zone):

New: August 2, August 31
First Quarter: August 10
Full: August 17
Third Quarter: August 24

[contentblock id=visitorsidebar][contentblock id=6]
2017-06-05T12:05:13+00:00Monthly Astronomy Article|