September Moon At Ascending Node #1

1sep-ascending-node   Thursday September 1st the new Moon will be crossing the plane of the ecliptic moving north relative to the ecliptic. This is known as the ascending node, one of two intersections the Moon’s orbital path has with the ecliptic. The ecliptic is actually the Earth’s orbit and the Moon’s orbit is inclined about 6o from the ecliptic. So there are two node intersections, the ascending and descending nodes.

   Coincidentally the new Moon and the Sun will also be together for an annular solar eclipse.

   Does our Moon actually go around the Earth as many graphics show? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*

*Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

September Annular Eclipse

node-close_up   The solar eclipse on Thursday September 1st, will have been brought to us by the nodes. No the nodes are not a scientific nor a musical group, but rather the nodes represent an intersection between the orbital path of our Moon, or another planet, with the Earth’s orbital path, the plane of the ecliptic.
   There are two nodes or intersections, the ascending node and the descending node. There are two nodes because the planets as well as our Moon do not orbit the Sun on the same level, or plane as does the Earth. Their respective orbits are inclined (tilted) away from the plane of the ecliptic by varying amounts such that they will at times appear below or above the plane of the ecliptic. There will be two times each orbit around the Sun where the planet or our Moon will be on the plane of the ecliptic as it crosses moving from below setting up the ascending node or from above toward below, setting up the descending node.
   So what is the significance of the nodes? The significance is all about timing. If the time of the new Moon phase, for example, occurs at or near the time for a node crossing then there will be a solar eclipse. Remember that at this moment the Moon is on the plane of the ecliptic and is more or less directly between the Earth and the Sun. More importantly, if the times are exact or very close there will be either a total solar eclipse or an annular solar eclipse. 29april-annular_eclipse-ani   During an annular eclipse the Moon is somewhere near its apogee, or most distant point for that particular orbit. This annular eclipse happens 5 days before the Moon reaches apogee on September 6th but the Moon is still far enough away so that its apparent diameter is less than the Sun’s apparent diameter. Both are around 0.5o or 30′ in apparent diameter, however for this annular eclipse the Moon will be about 3% smaller and not be able to completely cover the Sun at mid-eclipse. Instead at mid-eclipse there will be a ‘ring of fire’, the annulus, around the Moon.
   Thursday September 1st the new Moon phase is at 9:03 UT and the Moon is at its ascending node about 6 hours later at 15:27 UT. The Moon makes first contact with the Sun at 6:23 UT; maximum or mid-eclipse is at 9:06 UT; and the eclipse officially ends with last contact at 12:00 UT.
   To sort of complete this story, if there is a solar eclipse, no matter how total or less than total, there will be a lunar eclipse two weeks away at full Moon phase. Eclipses occur in pairs so this pair will be completed with the penumbral lunar eclipse at full Moon on September 16th.Moon Grazing the Earths ShadowFull Moon on September 16th is at 19:05 UT, about 19 hours after the Moon is at its descending node, 11:57 UT September 15th. Because of the time difference, the angle the Moon follows through the Earth’s shadows does not cross the dark inner umbral shadow but rather only takes it across the less noticeable outer penumbral shadow. Unless you knew about it you may not notice a slight dimming of the reflected moonlight.

   For an outstanding web site about all eclipses including information for these two eclipses go to the Hermit Eclipse web site.
   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

Mercury Begins to Retrograde

mercury-retrograde-ani   The innermost planet Mercury is about 2 weeks after its Greatest Eastern Elongation on August 16th. As the name suggests Mercury has been on the east (left) side of the Sun and visible in the evening skies after sunset. From a combination of the Earth’s and Mercury’s orbital speed and angle relative to each other Mercury is now seen as moving westward toward Inferior Conjunction on September 12th. Mercury will continue moving westward until it reaches its Greatest Western Elongation on September 28th.
   Retrograde or westward motion is probably best known as it relates to the apparent motion an outer planet relative to the Earth has. mars-retrograde-aniThis apparent westward motion comes about as the Earth, moving faster than an outer planet, catches up with and passes the slower moving outer planet. As this happens the outer planet appears to slow down, pause, then move westward for a period of time lasting from days to weeks. At some point the angle between the Earth and the outer planet has shifted enough so that it appears as if the westward motion has ended and the outer planet resumes its direct or eastward motion around the Sun.
   For an outer planet this is an apparent motion relative to the stars in the background, while for the two inner planets they really do move westward as they orbit the Sun between eastern and western elongation, and along the way passing between the Earth and the Sun at inferior conjunction.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

Moon Near Beehive Cluster


   Monday morning August 29th the thin waning crescent Moon will be a few degrees away from the open star cluster known as M-44, or the Beehive Cluster.

   
   
   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

Triple Planetary Conjunction

    Over the next few evenings the inner planet Venus and the planet Jupiter will pass each other coming as close as about 0.07o. That is considerably smaller than the diameter of the full Moon. As this graphic shows the planet Mercury is also part of the scene and the three planets are within 5-6o of each other. With binoculars the planetary trio is easily seen, and through the eyepiece of a telescope you can easily fit Venus and Jupiter.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

Moon Near Aldebaran

Thursday morning August 25th watch for the last quarter Moon to be either close to the star Aldebaran or occulting Aldebaran – depending on your location. This occultation will be visible from around Hawaii across the Pacific Ocean toward the southern United States of America and Estados Unidos de Mexico.
   Aldebaran is the reddish and brightest star in the constellation of Taurus the Bull and from mythology Aldebaran represents the angry eye of the bull. Aldebaran is also part of the v-shaped group of stars forming the face of the bull, and this group of stars, the Hyades, is also an open star cluster – a group of stars clustered together by their respective gravitational forces. The Pleiades, looking like a small dipper, is another nearby open star cluster and part of the Taurus constellation.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

2 Planets and 1 Star


   Wednesday evening August 24th the planet Mars will be within about 4o from the planet Saturn and 2o from the reddish star Antares in Scorpius the Scorpion. This is about the closest the three will be to each other this year.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

Sun Not In Virgo

   
According to the pseudoscience of astrology the Sun enters the constellation of Virgo the Maiden on Monday August 22nd. When in fact the actual position of the Sun today is toward the west and still within the boundaries of the constellation of Leo the Lion.

   Read a little more about how astrology has the Sun incorrectly placed in a previous blog, and in another blog discussing the effects of precession.
   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

August Moon at Perigee

   The Moon reaches perigee, (minimum distance from Earth), this month on Monday August 22nd. At that time the Moon will more or less be at a distance of 28.77 Earth diameters (367,050 km or 228,074 miles) from the Earth.
   Does our Moon actually go around the Earth as this graphic shows? From our perspective on the Earth the Moon appears to circle around the Earth. However, in reality, the Moon orbits the Sun together with the Earth*


   On the day of the lunar perigee the 19.6-day old waning gibbous Moon rises a couple of hours before midnight and is over the southern horizon at sunrise the following morning. Interestingly the Moon is sort of surrounded by planets – both kinds.
   
   
   
   
   
   
   *Click here to read my 2006 Scope on the Sky column “The Real Shape of the Moon’s Orbit”. (PDF)

   Read this very informative article about the Earth-Moon system and their orbital motions, written by Joe Hanson. “Do We Orbit the Moon?”

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.

August Moon at Descending Node

apr5-descending-node
   Friday August 19th the waning gibbous Moon will be crossing the plane of the ecliptic moving south. This is known as the descending node, one of two intersections the Moon’s orbital path (dark green line) has with the ecliptic.
   
   
   
   

   On the day of the node crossing the 17-day old waning gibbous Moon rises before midnight local time and is over the southern horizon at sunrise.

   
   
   

Click here to go to the Qué tal in the Current Skies web site for monthly observing information, or here to go to bobs-spaces.