What’s Up in the Sky June, 2008
By Peter Burkey

We live in a more or less placid, stable world. Changes occur, but slowly. Although recent events may indicate otherwise, most of us live full lives never encountering a natural disaster more violent than a storm and so we are fairly complacent. The geological record, however, is clear – widespread devastation and major catastrophes are common occurrences albeit on a very long time scale. But in just the last century, there have been bizarre natural events. One such event happened 100 years ago next month.

Early in the morning of June 30, 1908, the Tungus people of central Siberia were violently awakened by a giant fireball racing across the sky. Soon thereafter an enormous explosion shook the ground, followed by searing winds and a huge forest fire. Some folks were thrown into the air, even knocked unconscious. Horses bolted, windows shattered, and thousands of trees were leveled. The explosion produced an atmospheric shock wave that circled the Earth twice. So much dust was kicked up into the atmosphere that for two days Londoners could read a newspaper at night illuminated by the scattered light.

Little was known about the Tunguska Event, as it came to be called, since the Czarist government in Russia considered it to be of little importance, having occurred in such a remote area among backward inhabitants. In fact, it wasn’t until 1930 that an expedition of scientists journeyed to the area to gather evidence and hear eyewitness accounts. Slogging through endless swamps and plagued by voracious mosquitoes, they found complete devastation with trees burned or stripped bare lying on the ground, all pointing away from the point of impact. What they did not find, however, was an impact crater or any evidence of pieces of the original object.

Many hypotheses were proposed to explain the event. Among the more interesting were a piece of antimatter completely annihilated when striking the normal matter of Earth, or a mini black hole that passed through the Earth in Siberia and out the other side. Some even postulated than an alien spacecraft from an advanced civilization experiencing engine trouble crashed. More plausibly it was thought to be a comet fragment that exploded high above the ground, hence no crater.

The most recent theory, based on our better understanding of atmospheric meteorite explosions and supported by new evidence, suggests that it was an exploding stoney meteorite. No matter what its cause, we should be glad it happened in a distant remote area or it packed the wallop of a large H-bomb. Perhaps the next time we will have advanced warning and be able to avoid the devastation caused by uninvited visitors from up in the sky.

Here are this month’s viewing highlights:
Planets this month: Mars closes in on Regulus and Saturn low in SW in the early evening. Jupiter continues to dominate the southern predawn sky.

June 3: New Moon – closest of the year.
June 7-9: Watch Moon pass line of objects Mars, Regulus, Saturn.
June 10: First quarter Moon.
June 18: Full Moon.
June 26: Last quarter Moon.
June 30: Mars and Regulus form close pair.

What’s Up in the Sky May, 2008
By Peter Burkey

It was Saturday, September 15, 2007, at 11:45 a.m., when 74-year-old Justina Limache, a farmer in Carancas, Peru, not far from Lake Titicaca, heard a “thunderous roar from the sky.” Scared, she ran into her house clutching her 8-year-old granddaughter. For the next few minutes, she feared her house would be destroyed by rocks raining down on the roof. What Justina Limache did not know was that a meteorite had fallen near her home in the little farm community of about 2,000 people near the Bolivian border. The impact left a crater some 45 feet across and spewed debris as far as 500 feet! Luckily, no one was injured.

Was this a rare, isolated event or a reminder of the potential danger we face living on planet Earth? Yes. Meteorite impacts are relatively rare but every now and then one poses a real threat.

Clearly, impact events are common in the solar system. One look at our Moon reveals a surface pockmarked with craters and just about every other planetary satellite we have imaged shows the same characteristic features. Here on Earth, most meteorite craters have been wiped out by wind, water, or geologic activity with some notable exceptions such as the Barringer Meteor Crater in Arizona. However, astronomers believe that Earth must have been impacted numerous times throughout history, with most being of the small, localized nature, but a few causing global devastation.

Could it happen again? Probably. But the fact that most of the debris left over from the solar system’s formation has already been swept up makes the probability of such an event extremely small – but not zero. For this reason, a small number of scientists are constantly monitoring the skies for “NEOs” – near Earth objects, mostly asteroids whose orbits intersect (or come close to) that of Earth. Several such objects have been discovered in recent years and some have passed as close as the Moon. There have even been discussions regarding ways to deflect or destroy such harbingers of disaster (remember the movie “Armageddon”?).

Given the remote possibility of such an event, we probably have ample time to come up with a plan to protect us from uninvited visitors from up in the sky.

This month in history:
May 1: One of Neptune’s moons, Nereid, discovered by Gerard Kuiper – 1949
May 6: Neil Armstrong ejects safely before Lunar Landing Research Vehicle crashes – 1968
May 24: Mercury astronaut Scott Carpenter becomes first American to eat food in space – 1962
May 28: Rhesus monkeys Able and Baker are first primates in space – 1959
May 31: European Space Agency formed – 1975

Here are this month’s viewing highlights:
Planets this month: Saturn and Regulus in Leo form a striking close pair all month. Mars fading in west at dusk. Mercury visible low in WNW at dusk first half of month. Jupiter continues to dominate southern predawn sky.

May 5: New Moon.
May 6: Mercury between thin crescent Moon and Pleiades – one hour after sunset.
May 11: First quarter Moon
May 19: Full “Blue” Moon – third Full Moon of the season.
May 21-24: Use binoculars to see Mars pass through Beehive cluster.
May 27: Last quarter Moon.

What’s Up in the Sky April, 2008
By Peter Burkey

This month marks the anniversary of an event not well known outside the astronomical community. On April 20, 1920, the Shapley-Curtis debate was held at the National Academy of Sciences in Washington, D.C. The topic was the nature of “spiral nebulae” which astronomers had observed since the 1840’s. On one side was Harlow Shapley from the Mount Wilson Observatory, who argued the spiral nebulae were relatively small objects located in our own galaxy. Opposing him was Heber D. Curtis of the University of California’s Lick Observatory and a proponent of the “island universe” theory that each nebula is a rotating star system similar to the Milky Way and located far beyond its boundaries.

The problem was neither side could produce conclusive evidence to determine the distances to the spiral nebulae. A young man then studying astronomy at the Yerkes Observatory near Chicago would finally make such a determination four years later. That young student was Edwin Hubble.

It may seem strange, but distances in astronomy are very difficult to measure. The problem is that in order to know how far away something is you have to know how bright it is really (its intrinsic brightness).

Assisted by Milton Humason, Hubble observed a certain type of pulsating star, called a Cepheid variable, whose intrinsic brightness is related to its rate of pulsation. Their measurements enabled them to calculate the star’s actual brightness – 10,000 time that of the sun! In order for it to appear as dim as it did in their photographs it had to be very far away – 2.5 million light years -well beyond the confines of the Milky Way. The Shapley-Curtis “debate” was settled.

Today astronomers still expend great energy and build amazing instruments to measure stellar and galactic distances with ever increasing accuracy. These data have unveiled mysteries of the universe long sought by humans. In addition to its size and structure, the history, evolution, and future of the universe can now be studied. All this is possible through the careful measurements of what’s up in the sky.

This month in history:
April 5: Pioneer 11 launched – 1973
April 11: Apollo 13 launched – 1970
April 12: Yuri Gagarin becomes first human in space – 1961
April 12: Columbia is first space shuttle to be launched – 1981
April 17: Apollo 13 returns to Earth – 1970
April 20: Shapley-Curtis debate – 1920
April 24: China is fifth nation to launch satellite – 1970

Here are this month’s viewing highlights:
Planets this month: After sunset Saturn is in SE, left (east) of the star Regulus and Mars is in the SW, just below the twins Castor and Pollux. Mercury becomes visible near western horizon at month’s end. Jupiter dominates predawn southern sky.

April 4: Thin crescent Moon near Venus just before sunrise – challenging.
April 5: New Moon.
April 8: Watch crescent Moon pass in front of Plieades – spectacular.
April 12: First quarter Moon.
April 20: Full Moon.
April 28: Last quarter Moon.

What’s Up in the Sky March, 2008
By Peter Burkey

A parade of planets dominates the sky this month and my two favorite constellations are both easily visible.

If you face south, Mars is nearly overhead. Saturn follows close behind below the constellation Leo, the Lion, just east of the star Regulus. For the other three naked-eye planets, Mercury, Venus, and Jupiter, you have to wait until the hour before sunrise. Jupiter will be the brightest object in the southeast. In the east Venus is even brighter but much lower and harder to spot as the month progresses. Much dimmer Mercury is just to the right of Venus. They are joined by a thin crescent moon on the 5th. Use binoculars for that one.

On the few clear nights we have had in February you probably saw Orion, the Hunter, standing tall in the southwest but you may have missed the Big Dipper which was lower and less conspicuous in the northeast. This month they can still be found on opposite sides of the sky but now the Big Dipper, standing upright on its handle, is also about halfway up and easier to pick out.

Technically the Big Dipper is not a constellation but a star pattern that is part of a larger constellation, in this case Ursa Major. But comparisons between it and Orion are interesting. Both contain seven main stars with distinctive three-star patterns within – the belt of Orion and the handle of the Big Dipper. Also, the majority of stars that form each are themselves members of the same cluster with those in the Dipper about 80 light years (LY) away while Orion’s stars average 1000 to 1500 LY.

One major difference between the two is their neighbors. The Big Dipper sits alone, far from other bright constellations, while Orion traverses the sky surrounded by friends.

Orion’s departure to the west and the Big Dipper’s ascent in the northeast usher in the constellations of spring, soon to be up in the sky.

This month in history:
March 1: George O. Abell born – 1927
March 5: Voyager 1 makes closest approach to Jupiter – 1979
March 13: Uranus discovered by William Herschel – 1781
March 16: Carolyn Herschel born – 1750
March 18: Soviet rocket explosion at launch pad kills 48 workers – 1980
March 22: Comet Hale-Bopp passes closest to Earth – 1997
March 23: Russian space station, Mir, reenters atmosphere -2001
March 29: First fly-by of Mercury made by Mariner 10 – 1974

Here are this month’s viewing highlights:

Planets this month: Venus and Mercury form a close pair near the eastern horizon 30 minutes before sunrise, best viewed early in the month. Saturn remains close to the star Regulus. Mars is just west of the stars Castor and Pollux. Jupiter shines brightly in the SE at dawn.

March 5: Use binoculars to see thin crescent Moon close to Venus and Mercury very low in the east just before dawn
March 7: New Moon
March 14: First quarter Moon.
March 20: Spring begins at 1:48 a.m. EDT when the Sun reaches vernal equinox.
March 21: Full Moon.
March 29: Last quarter Moon.