Skywatch April 2005

by Julene M Johnson

Skywatch Stargazing Archives

A fairly rare hybrid or annular/total solar eclipse occurs this month, followed by a penumbral lunar eclipse. This month’s article will explain why some New Moons are solar eclipses and others are not, as well as explaining just what this Hybrid Eclipse is anyway.

Mercury, Mars, Jupiter & Saturn are visible during April. Venus is still traveling too close to the Sun to observe. The annual Lyrid Meteor Shower occurs, though it is dampened by a Full Moon.

SOLAR ECLIPSE MECHANICS
Solar Eclipses occur when the New Moon (Moon & Sun) is conjunct either the North or South Lunar Node. The Lunar Nodes are points in space where the Moon’s orbit crosses the Ecliptic and the Earth’s orbital plane. When the Moon conjuncts its Node, it too is on the same plane as the Sun and Earth. This allows the Moon to pass between the Sun and Earth and cover the Sun. The orb of the conjunction determines whether a total or partial eclipse occurs.

Here a few figures of when we can expect a Solar Eclipse to occur. If the conjunction between the New Moon (Moon & Sun) and either Lunar Node has an orb of 9 degrees 55 minutes or less, either a Total or Annular Solar Eclipse will occur. If the conjunction of the New Moon and one of its nodes is between the previous orb and 11 degrees and 15 minutes, then the eclipse can be either total or partial. If the orb is beyond 11 degrees and 15 minutes and up to 15 degrees and 21 minutes the eclipse will be partial. It is possible, but not always probable, for a Partial Solar Eclipse to occur when the New Moon is as far as 18 degrees and 31 minutes from the Lunar Nodes.

During a partial eclipse the Moon only covers part of the Sun’s disk because the orb is too wide for the Moon to fully pass in front of the Sun as she rotates with the Earth even though all are on the same plane. During both a total and annular eclipse, the Moon passes fully in front of the Sun. With a Total Solar Eclipse the Moon fully covers the Sun’s disk, while an Annular Solar Eclipse will leave a ring of the Sun’s disk showing around the Moon when she passes in front. Which one occurs depends on whether or not the apex of the Moon’s shadow reaches the Earth. When the apex of the Moon’s shadow reaches Earth, a Total Eclipse occurs. When the Moon is too far away for the apex of her shadow to reach Earth, an Annular Eclipse occurs where a “ring of fire” becomes visible around the Moon as she passes in front of the Sun.

HYBRID ECLIPSE
Now in Hybrid or Total/Annular Eclipse, such as the one occurring on April 8th, both total and annular results occur within the eclipse. If we think of hybrid plants being a cross germination between two different varieties, the name makes sense. This mechanics of a hybrid eclipse make sense when you consider that the difference between a Total and Annular Solar Eclipse is based on how far the Moon is from the Earth and whether or not her shadow can reach. When both total and annular occur during the same eclipse it is the curvature of Earth that comes into play to create that phenomenon. Some points of the Earth’s surface along the eclipse path are close enough to the Moon for her shadow to reach while other parts of the Earth’s surface are not. Usually Hybrid Eclipses begin as annular, become total and then go back to annular. This is the case on April 8th; but you would have to be on a ship in the South Pacific somewhere between Tahiti and Costa Rica to see the total portion of this eclipse. That is where the small portion of Earth’s surface curves up to reach the Moon’s umbral shadow. These hybrid eclipses seem to occur with inconsistent frequency. The next one won’t be until November 3, 2013. The last one occurred on March 29, 1987. Another occurred a half a year before that on October 3, 1986. The one prior to that was on April 28, 1930.

SOLAR ECLIPSE OF APRIL 8TH’
The Annular Eclipse (path of the Moon’s umbral shadow) begins southwest of New Zealand, crosses the South Pacific where it briefly becomes total for less than a minute, extends in its annular state to Central America and ends in Venezuela where observers will see a ring of fire around the setting Moon -- which will be at sunset, of course. A Partial Eclipse (path of the Moon’s wider penumbral shadow) will be visible in New Zealand, Antarctica, Caribbean, South America, and the southern United States. If you live in the US and wonder if you can see part of the eclipse, do this: draw a curved line beginning in mid New Jersey, go through Kansas City and end in San Diego. The farther below that line you live, the greater the percentage of the eclipse you will see. The eclipse begins at 17:51 GMT and ends at 23:20 GMT. Mid-totality occurs at 20:15 GMT.

MOON DATA
A Third Quarter Moon occurs on April 1st at 7:50 p.m. EST. Those of us who observe daylight savings time will turn back our clocks on April 3rd at 2:00 a.m. The Moon reaches perigee on the 4th at 7:11 a.m. EDT. She will be 228,970 miles from Earth. The New Moon occurs on April 8th at 4:32 p.m. EDT and is a Hybrid Solar Eclipse. The First Quarter Moon occurs on April 16th at 10:37 a.m. EDT. Later that day the Moon reaches apogee at 2:41 p.m. and will be 251,223 miles from Earth. On the 22nd, the Moon occults Jupiter over the South Indian Ocean, the southern half of Africa and part of Antarctica. The Full Moon occurs on the 24th at 6:06 a.m. EDT and is a Penumbral Lunar Eclipse or an Appulse. On April 26th the Moon occults Antares the red hued alpha star of Scorpius who rivals Mars and is the heart of the Scorpion. A second perigee occurs this month on the 29th at 6:13 a.m. EDT. This time the closest distance she reaches to Earth is 229,304 miles.

LUNAR ECLIPSE OF APRIL 24TH
The lunar eclipse begins at 7:49 GMT and ends at 11:59 GMT with the mid-eclipse being at 9:54 GMT. During a Lunar Eclipse, the Earth is between the two luminaries. The Earth casts a shadow on the Moon. An Appulse occurs when the Moon only enters the penumbral shadow of the Earth. A penumbral shadow is the space of partial light and partial shadow that exists between full light and full shadow (umbra). The beginning of this eclipse is visible over the Americas, New Zealand, Eastern Australia, Eastern Indonesia, and Antarctica. The end of the lunar eclipse is visible over western North America, Mexico, Indonesia, New Zealand, Australia, Eastern Asia and Antarctica.

LYRID METEOR SHOWER
The Lyrid Meteor Shower peaks on April 22nd. Occurring just 2 days before the Full Moon, the peak display will not be so great, yielding only about 10 visible meteors per hour. The meteors radiate from the constellation Lyra the Harp of Orpheus that could lull the wildest beasts. Lyra lies high above the Ecliptic between Cygnus the Swan and Hercules. Lyra rises above the northeast horizon of North America around 9:30 p.m. on the evening of April 21st and gains enough height for observing the shower in the early morning hours of the 22nd. The best bet to catch a falling star is on the morning of the 22nd after 2:00 a.m. Observers in Australia will not likely catch a glimpse of the Lyrid Shower. Lyra does not rise until about 2:30 a.m. and remains very low along the horizon until dawn.

MERCURY VISIBILITY
Mercury is a morning star this month. Australian observers will have much better luck observing the messenger than those in North America. Start watching for Mercury to rise over Australia around 5:00 a.m. on the 15th. From then until the end of the month, you should have about an hour to catch a sight of the innermost planet. Mercury reaches greatest western elongation on the 26th at 1:00 p.m. EDT. He will be as far west from the Sun as he can travel: 27 degrees.

Observers in North America can try to catch sight of him on that morning, but he rises just 30 minutes before the Sun and the encroaching glow of dawn will make him very hard if not impossible to see. Mercury begins the month retrograde and stations direct on the 12th at 3:46 a.m. EDT.

VENUS
Venus is not visible this month. She is “combust” or conjunct the Sun within an orb of 8 degrees. When a planet is combust, it is not visible under any conditions. Next month Venus will move from combustion status, to fall “under the Sun’s beams”. Under the Sun’s Beams is applied to planets that are within an 8 to 17 degree orb from the Sun. Planets under the sun’s beams can be seen if they are very bright and the atmospheric conditions are good. Venus is the brightest planet so tune in next month and see what you can see.

MARS VISIBILITY
Mars moves 21 degrees this month making his eastward direct motion across the fixed stars of the zodiac constellations quite apparent. He begins the month midway through Capricornus and ends the month in Aquarius. Remember that the constellations represent the sidereal zodiac and ayanamsha (the difference between the two zodiacs) is currently about 23:55:50.

Observers in North America will find Mars rising around 4:00 a.m. in the beginning of April and around 3:00 a.m. by month’s end. The red planet will remain observable until the sunrise brightens the morning sky, diminishing his visibility.

Observers in Australia will find Mars rising around 1:30 a.m. this month and remaining visible until dawn.

JUPITER VISIBILITY
Jupiter moves about 3.5 degrees backwards or west this month against the fixed backdrop of the sky. This small retrograde movement is not likely to be that noticeable. Jupiter will be visible all night long this month, rising with the setting Sun. Jupiter reaches aphelion on April 14th. This is the farthest he can be from the Sun on his orbital path. The distance is 507.2 million miles.

North American observers will find Jupiter rising around 7:00 p.m. at the beginning of the month, though you may have to wait until the skies darken to find him above the eastern horizon. As Jupiter climbs higher in the evening sky, notice the bright star below him. That will be Spica the alpha star of the constellation Virgo that rises almost straight up out of the east. Jupiter will cross the sky through the night to set around 6:15 a.m. on the 2nd. The glow of dawn will prevent the observation of Jupiter dipping below the horizon until a bit later in the month. By month’s end, Jupiter will rise over North America around 5 o’clock, while it is still good and light out. At sunset, Jupiter will be well above the eastern horizon. On the 30th he sets before dawn at around 4:15 a.m. Facing west, Spica will be to the left of Jupiter as Virgo, heads sideways into the western horizon.

Australian observers will find Jupiter rising around 6:30 at the beginning of the month and will also have to wait for the skies to darken to locate him above the eastern horizon. He rises early and earlier as the month progresses. By month’s end he will rise around 4:30 p.m. and be higher above the eastern horizon at sunset. Facing east, Spica will be the bright star to the right of Jupiter, as Virgo climbs sideways over the horizon. Jupiter sets over Australia around 6:45 a.m. on April 1st and around 4:30 on April 30th as Virgo heads almost straight upside-down into the western horizon.

SATURN VISIBILITY
Saturn stationed direct last month and is still moving too slowly to be noticeable. He will cover only a little over a degree of eastward movement through the constellation Gemini. At sunset, Saturn will be high in the darkening southwest North American sky near the Midheaven. He sets around 2:15 a.m. on April 2nd. By month’s end, Saturn will be fairly high in the western sky at sunset about midway between the Zenith and the horizon – in about the 8th/9th house cusp area. By April 30th, he sets around 12:30 a.m.

Observers in Australia will locate Saturn near the highpoint of the ecliptic in the north on the 1st at sunset. He sets around 11:45 p.m. on the 1st. Saturn will be lower along the north-northwest horizon at sunset by month’s end – in about the mid 8th house area. He will set around 9:45 p.m. on the 30th.

THE MOON DANCES WITH THE PLANETS in N.AMERICA
The Moon will rise to the right of Mars around 3:45 a.m. on the morning of the 3rd in the southeast sky. As the skies darken on the 15th, look for Saturn just below and to the right of the Moon. By the time Saturn sets around 1:30 a.m. the Moon will be almost directly above. On the evening of the 22nd, look for Jupiter to the left of the Moon. By the time the glow of dawn approaches, the Moon & Jupiter will be nearly set, with Jupiter dancing above and slightly left of the Moon. By the evening of the 23rd, the Moon will have danced on past in her eastern direction. At which time Jupiter will be to the right of the Moon.

THE MOON DANCES WITH THE PLANETS in AUSTRALIA
On the morning of the 4th, the Moon will rise just ahead of Mars around 1:00 a.m. As the pair climbs higher into the eastern sky, Mars can be located slightly below and to the left of the Moon. By the morning of the 5th, the Moon will have moved considerably past Mars, who will now dance above the luminary and to the left. The Moon passes Mercury on the 7th and will be just below the planet on the morning of the 8th. It is doubtful that sunrise will allow you to spot Mercury hanging just above the New Moon this morning. On the 16th as the skies darken after sunset, look for Saturn above and to the left of the Moon. The pair will set side by side around 10:45 p.m. with Saturn to the left. On the 22nd, look for Jupiter just right of the Moon. As the pair dance across the sky through the night, culminate and begin to descend, you’ll notice the Moon nearly on top of Jupiter around 1:30 a.m. The pair set together around 5:00 a.m.

SKY MAPS ARE LOCATED IN THE OCA MAIN PUBLIC LIBRARY OF…..
Moon & Mars over the northern hemisphere on the morning of April 3rd.
Moon & Mars over the southern hemisphere on the morning of April 4th
Moon, Jupiter & Saturn over the northern hemisphere after sunset on the 22nd
Moon, Jupiter & Saturn over the southern hemisphere after sunset on the 22nd
http://www.astrocollege.com/campus/libraries.cgi

Happy Stargazing! Remember stars twinkle because they generate their own light and planets don’t because their atmosphere reflects the light of the Sun. Please remember not to look at an eclipse with your naked eye or with the aid of binoculars or a telescope as the results can be blinding.