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SKY REPORTER: June 2012

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Sky Data

Earth and Crescent Moon from ISS

Waning crescent Moon viewed from the International Space Station September 5, 2010.

Credit: NASA


Friday June first, sunrise is at 5:27 a.m. Eastern Daylight Time. That evening the Sun located in the constellation Taurus sets at 8:21 p.m.

On June 20, our longest day of the year, sunrise is at 5:25 a.m. and sunset arrives at 8:30 p.m. On this date the Sun is above the horizon for 15 hours and six minutes.

The last day of the month the Sun is in Gemini, rising at 5:28 a.m. and setting at 8:31 that evening.

In New York City at the start of June the Sun is above the horizon for 14 hours, 55 minutes. On the longest day June 20 that number rises to 15 hours and six minutes. Then time between sunrise and sunset begins to diminish and we lose three minutes of direct sunlight by the end of June. On our first day of summer Earth’s northern rotation axis is at its maximum tilt toward the Sun. The Sun’s position at solar noon that day reaches its annual peak of 72.7 degrees of arc above the horizon at our location.

Average overnight temperatures in Central Park rise from 59 degrees Fahrenheit on the first of June to 67 degrees on the last day of the month.

Principal Phases of the Moon are:

Full Moon June 4
Last Quarter June 11
New Moon June 19
First Quarter June 26

Sky Cast

On June 1 the planets Mercury, Venus, Mars, and Saturn are all above the horizon at sunset. Mercury and Venus are near each other low in the west as twilight fades. Both are too close to the Sun to be casually observed. Mars is high in the southwest during early evening and does not set until 1:45 a.m. the next morning. Saturn is near the meridian after sunset on June 1 and remains above the horizon until 3:21 a.m. Uranus is near the border between Pisces and Cetus and rises at 2:30 a.m. Neptune, now considered the most distant of the Sun’s family of planets, is in the constellation Aquarius and rises at 1:08 the morning of June second. Jupiter is now also visible before dawn rising at 4:42 a.m.

During the evening of June 1 the waxing gibbous Moon is near the border of Virgo and Libra, 17 degrees of arc southeast of Saturn. First magnitude star Spica, 260 light years from us, appears five degrees south of the slightly brighter spectacularly ringed planet.

The evening of Sunday June 3, a bright waxing gibbous Moon (indistinguishable from a Full Moon by most observers without the help of optical aid) is in Ophiuchus, about five degrees north of first magnitude Antares, brightest star in Scorpius. Antares is a red supergiant in the last stages of its existence, located about 600 light years from Earth.

June 4 is the night of the Full Moon, traditionally known as the Full Strawberry Moon or Full Rose Moon.

Venus on Sun's Edge During Transit

Disk of Venus at Sun’s edge during 2004 Transit.

Credit: D. Kiselman, et al. (Inst. for Solar Physics), Royal Swedish Academy of Sciences


This year’s long anticipated Transit of Venus across the disk of the Sun occurs in the early evening of Tuesday June 5, beginning with first contact of the Venusian disk with the Sun’s apparent edge at 6:03:50 p.m. EDT. Second contact, when the planet’s outer edge reaches the Sun’s disk, is predicted for 6:21:22 p.m. Regardless of our local weather, you’re welcome to join us at the American Museum of Natural History beginning 5:30 that afternoon in the Cullman Hall of the Universe. We’ll be watching the transit event in real time via NASA simulcast from a high altitude site on Mauna Kea volcano, Hawaii. The event is free with Museum admission. Enter at 81st Street (Rose Center – Hayden Planetarium). I look forward to seeing you there.

Astrophysicist Jackie Faherty provides more Transit details and NASA’s transit/eclipse guru Fred Espenak gives additional information at his website.

Transits of Mercury and Venus were first predicted by Johannes Kepler 385 years ago based on his laws of planetary motion. These are rare events, occurring in pairs separated by more than a century. During the 18th and 19th centuries Transits of Venus held promise for triangulating the distance to that planet thereby determining the size scale of the Solar System. However, a visual distortion called the “black drop effect” attributed to Earth’s atmosphere, small telescope size, limb darkening of the Sun’s edge, or some combination of these, prevented precise timing required for such measurements.

In a way, the transit of Venus is similar to annular eclipses of the Sun such as that seen last month. During an annular eclipse the amount of sunlight reaching observers is significantly diminished but not entirely blocked. During such events the moon is too far from Earth to completely obscure all direct sunlight, as would be the case in a total solar eclipse. As a result a bright ring of light is visible around the eclipsing Moon. During transits of the Sun Venus, although four times the diameter of the Moon is many times further from us than our lunar neighbor and the Venusian disk looks tiny compared with that of the Sun. Nevertheless, Venus does block some light and the brightness of the Sun is diminished by a miniscule, but measureable amount. Timing the event’s stages from widely separated points on Earth, could allow us to determine Venus’ distance from us, thereby assigning a specific value to relative distances of other planets. That scenario would be practicable if not for the black drop effect that often seems to smear views of the Venusian disk immediately after second contact and before third contact of the planet’s edge with that of the Sun. During past centuries some astronomers travelled thousands of miles eager to discover the size of the Solar System and were frustrated by the annoying black drop. These distortions are not always seen, but have been also reported in several space satellite observations of Mercury’s solar transits. However, highly precise determinations of Venus’ distance are now made using radar.

However, transit observations of distant stars currently provide great results discovering and learning about extra-solar planets. The Kepler space observatory (see our September 2011 and January 2012 posts) facilitates using this technique in the quest to find planets orbiting stars beyond the Solar System. Observations of this month’s Venus Transit from above the atmosphere using the Hubble Space Telescope, as well as studies of future transit events seen via Cassini mission cameras orbiting Saturn, are expected to help refine details of Kepler mission extra-solar discoveries.

Care must be taken during any attempt to directly view solar phenomena, otherwise blindness can occur. Repeating our advice from last month, only observers experienced with high quality solar filters, or capable of safely projecting the Sun’s image onto a surface to view the transit indirectly, should make such an attempt. Otherwise, it is advised to follow the event via internet or television.

The evening of Friday June 8 at 10 p.m. the brilliant star Arcturus with an apparent magnitude of -0.05 is at the meridian at an altitude of 68 degrees above the southern horizon. This star, one of the brightest in our sky, is about 37 light years from us.

Our earliest sunrise for this year is on Wednesday June 13th at 5:24 a.m.

In darkening twilight on the evening of Friday June 15, Mercury is low in the west. This elusive planet is now in Gemini and sets at 10:02 p.m. Mars then is in Leo and sets at 1:06 a.m. the morning of Saturday June 16. Next in the zodiac planetary progression is Saturn, seen among stars of Virgo and setting at 2:29 a.m.

At 12:16 a.m. June 16, Neptune in Aquarius rises at 12:16 a.m. It is followed into the eastern sky by Uranus on the border between Pisces and Cetus at 1:39 a.m. Next, Jupiter arrives in the eastern sky at 4:00 a.m. Then at 4:39 Venus makes its appearance above the east-northeast horizon.

Five a.m. in the twilight sky of Sunday June 17, a very thin crescent Moon is about three degrees to the upper right of Venus, becoming increasingly apparent in the early morning sky after its recent transit of the Sun. Jupiter, on the early morning of the 17th, is one degree of arc to the upper right of the crescent Moon.

Waning crescent Moon viewed from the International Space Station September 5, 2010. Credit: NASA

Summer starts in the northern hemisphere Wednesday June 20 at 7:09 p.m. At that time the Sun is directly above a point in the Pacific Ocean 593 miles west-northwest of Honolulu, about halfway between Kauai and Midway Island. The Sun is then in eastern part of Taurus, close to that constellation’s border with Gemini.

A half hour after sunset on June 21, the thin two day old crescent Moon is eight degrees above the western horizon and about seven degrees to the lower left of Mercury. Binoculars are a considerable help when searching for this planet.

The evenings of June 25 and 26, the waxing Moon is near Mars. Wednesday June 27 we have our latest sunset of the year at 8:31p.m. and during the evenings of the 27th and 28th the gibbous Moon is in Virgo near Saturn and Spica.

Sky Lore

In Africa within the Great Zimbabwe stone city it is believed early second millennium ancestors of the present day Shona people marked astronomical events such as the solstices with an observatory structure comprising a ring of stone walls over 200 feet in diameter, containing platforms and petroglyphs oriented to rising and setting of bright stars as well as the annual north-south traverse of the Sun. Richard Wade of the Nkwe Ridge Observatory in South Africa proposes that a large conical tower in the complex was constructed around 1300 A.D. to align with a supernova said to have occurred at that time. The Sena people of Zimbabwe have an oral tradition indicating their ancestors migrated to that region from the north, attracted by an unusually bright star seen in southern skies.

Brilliant Arcturus in the constellation Bootes has many mythological associations. In Shawnee legends it is linked to a warrior named White Hawk, who one day came upon a circular pattern of footsteps made in a forest clearing. He was mystified by the lack of any foot prints leading to the circle. After days and nights of observing he discovered the prints were made by a group of young women who descended and departed from the clearing in an airborne basket. Myths tell that these dancers were associated with the circlet of stars forming the Northern Crown, Corona Borealis.

The name Arcturus is derived from its ancient Greek description, The Bear Guardian, or Bear Driver. It alludes to the star’s proximity to stars of Ursa Major and Ursa Minor, the Great and Little Bears.

In 1933 beams of light from Arcturus were focused on photoelectric devices at four observatories to help inaugurate Chicago’s Century of Progress World’s Fair. It was thought light from this star, emitted during the city’s Columbian Exposition in 1893, had been en route to Earth during that entire 40 year interval. Now thanks to distance refinements provided by the European Space Agency’s Hipparchus astrometry satellite launched in 1989, we know light from Arcturus arrives at Earth after a journey of 36 years eight and a half months.

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