Star Calendar – August 2016

Star Calendar

August 2016

Star Calendar Planets:

Moon passes just out of reach of Earth’s sizable shadow on the 18th as it sets at dawn. It is very close to being, or not being, a technical penumbral encounter – but nothing observable will occur. Some eclipse tables will list this event, others will not. Both are correct! An annular solar eclipse will cross Africa and Madagascar on September 1st when the Moon’s shadow doesn’t quite reach the Earth.

Mercury makes its widest excursion from the Sun this month but does so doubly disadvantaged from our point of view. Firstly the ecliptic is dropping dramatically to the left of the Sun (aka the coming decent into fall) and secondly Mercury is passing rather south of the ecliptic line. At greatest elongation on the 27th, Jupiter and Venus have a lesser elongation but stand higher than Mercury in the evening – as they are north of the ecliptic just now.

Venus sets at 9:PM on the 1st and then about one minute earlier each day thereafter – but the Sun sets even earlier, gaining about a minute and 21 seconds each day – so Venus is a little higher each evening twilight relative to sunset but is lower each evening relative to the clock. During this month she will pass Regulus, Jupiter and Mercury.

Sun stands in the middle of Cancer as the month begins, crosses into astronomical Leo on the 9th and reaches Regulus on the 21st. If you recall where Jupiter stood (beneath the belly of Leo) at the extremity of his last loop (stationary on May 9), the Sun will reach that spot on September 5th.

Mars will make a striking equilateral triangle with Saturn and Antares, in the south on the 11th, but the Moon standing directly above him will make a distracting lozenge – or possibly blot out Antares. So perhaps on any other day it is a good time to contrast Mars with Antares as they approach one another. They are conjunct on the 23rd/24th.

Jupiter is in direct motion, meaning that he appears further leftwards each day against the stars. The Sun and Moon epitomize this motion and the planets execute variations and contrasts to this theme. Venus is moving more quickly than the Sun, Jupiter more slowly – and Venus will catch up on the 27th for a very close and very bright conjunction. That would be a night to find a 10 to 30 power telescope with either not too large an aperture or fitted with some filters, for Venus will be so close that she’ll mingle amongst the Moons of Jupiter. The pair will be low and due West at 8:15 PM at the very beginning of Nautical Twilight conditions. Find a good spot ahead of time.

Saturn is within the meridia of Scorpius, (though astronomically in Ophiucus) and stands above (north of) Antares. Mars will cut between the two on the 23rd/24th.

Perseid meteors statistically peak mid-month, but the gibbous Moon presents a liability then. There have been known to be earlier outbursts however, so gazing Perseus/Cassiopeia-wards earlier in the month may reward. The Aurigids peak in better conditions at the end of the month – but are above the horizon in the pre-dawn hours – raying from above Orion’s shoulder.

Star Calendar Days:

  1      Sunrise/sunset in Spring Valley at 5:52/20:12 (14h20m daylight)

  2      New Moon

  4      Mercury to right of young Moon, 8:45PM in West

          Also, lower to right, Venus

  5      Venus and Regulus conjunct in evening, latter probably washed out by sunset

  6      Moon just beneath Jupiter, setting by 9:30 PM in West

11      Moon, Mars, Antares, Saturn make a lozenge in SSW at 9:PM

12      Perseids peak – by statistics of the past

13      Saturn stationary to direct motion

16      Mercury at largest (but very low) angle from Sun for this appearance, 27 degrees

18      Full Red Moon (5:27 AM) sets in slight penumbral eclipse in early morning

23-25 Mars passes between Saturn and Antares, SSW in evening

27      Venus and Jupiter pass very close in West as Sun sets – should be quite bright

30      Mercury stationary to retrograde

31      Sunrise/sunset in Spring Valley at 6:22/19:30 (13h8m daylight)

About the Recent Lunar Eclipse

By the Dark of the Moon …

… indeed the last eclipse was darker than most — but not as dark as I had hoped for.


“LUNAR ECLIPSE DETECTS GLOBAL COOLING (BUT ONLY A LITTLE): On Sept. 27th, people on five continents watched the Moon pass through the shadow of our planet. Most agreed that the lunar eclipse was darker than usual. Little did they know, they were witnessing a sign of global cooling. But only a little.

Above: “The eclipse was truly dark,” says photographer Giuseppe Petricca of Pisa, Italy

Atmospheric scientist Richard Keen of the University of Colorado explains: “Lunar eclipses tell us a lot about the transparency of Earth’s atmosphere. When the stratosphere is clogged with volcanic ash and other aerosols, lunar eclipses tend to be dark red. On the other hand, when the stratosphere is relatively clear, lunar eclipses are bright orange.”

This is important because the stratosphere affects climate; a clear stratosphere ‘lets the sunshine in’ to warm the Earth below. At a 2008 SORCE conference Keen reported that “The lunar eclipse record indicates a clear stratosphere over the past decade, and that this has contributed about 0.2 degrees to recent warming.”

The eclipse of Sept. 27, 2015, however, was not as bright as recent eclipses. Trained observers in 7 countries estimated that the eclipse was about 0.4 magnitude dimmer than expected, a brightness reduction of about 33 percent.

What happened? “There is a layer of volcanic aerosols in the lower stratosphere,” says Steve Albers of NOAA. “It comes from Chile’s Calbuco volcano, which erupted in April 2015. Six months later, we are still seeing the effects of this material on sunsets in both hemispheres–and it appears to have affected the eclipse as well.”

Volcanic dust in the stratosphere tends to reflect sunlight, thus cooling the Earth below. “In terms of climate, Calbuco’s optical thickness of 0.01 corresponds to a ‘climate forcing’ of 0.2 Watts/m2, or a global cooling of 0.04 degrees C,” says Keen, who emphasizes that this is a very small amount of cooling. For comparison, the eruption of Pinatubo in 1991 produced 0.6 C of cooling and rare July snows at Keen’s mountain home in Colorado.

“I do not anticipate a ‘year without a summer’ from this one!” he says. “It will probably be completely overwhelmed by the warming effects of El Nino now under way in the Pacific.”

This lunar eclipse has allowed Keen measure the smallest amount of volcanic exhaust, and the smallest amount of resultant “global cooling” of all his measurements to date. And that is saying something considering that he has been monitoring lunar eclipses for decades.

“This is indeed the smallest volcanic eruption I’ve ever detected,” says Keen. “It gives me a better idea of the detection capabilities of the system (eclipses plus human observers), so when I go back into the 1800s I can hope to find similarly smallish eruptions in the historical record.”

Paul Davis

Star Calendar – September, 2015

Star Calendar

September 2015

Star Calendar Planets:

Moon will be waning as September opens and the ecliptic especially steep to the horizon in the morning. This circumstance will show especially thin and horizontal crescents on the 11/12th. New Moon begins the Hebrew new year (Rosh Hashanah) 5776 Anno Mundi. Moon’s ascending node currently lies where the Sun stands on the 24th, making this month an eclipse season. On the 13th the New Moon will be at an extreme apogee and its shadow will not reach the earth; a partial solar eclipse (for those near South Africa and the proximate part of Antarctica). However the Full and most perigee Moon of the 27–28th may well yield an especially dark lunar eclipse. A dark Moon is hard to see and is much more creepy than a red/yellow one; it looks like a giant stone hanging in the sky.

Mercury makes a large angle from the evening Sun on the 4th — but suffers from a shallow ecliptic. One may catch a peek around then, low in the west at 8PM. Mercury begins retrograde motion on the 17 and crosses the nearside of the Sun on the 30th.

Venus brightens to a maximum magnitude (for the year) of -4.8 on the 20th. She is receding from us and waxing in phase but is brightest while still crescent. The angular area Venus occupies in the sky diminishes as she recedes, that area being maximal on the 21st — when the waxing phase briefly overtakes the diminishing of receding distance.

Sun crosses the celestial equator on the 23rd, its center crossing at 4:21AM. The day of equinox is still 3 minutes longer than night though, a 12-hour-night waits for the 25/26th. Success in balancing eggs on their ends at equinox only indicates a greater patience and diligence in the attempt. There is no special gravity or balance-energy that day. Sorry.

Mars defers to Venus these mornings and passes (slightly dimmer than and) close to Regulus on the 25th, while bracketed by Venus above, Jupiter below.

Jupiter will be noticed emerging from his sunbath some fine morning this month, appearing below and much brighter than Regulus in the east. Weather and horizon permitting, look for it while scouting for old crescent Moons in the east at 6AM on the 11/12th.

Saturn is in the lower SW in the evening, and is the brightest celestial object in the vicinity. The Moon will be nearby on the 18th. Continue reading