by Kim Malville
The skies of July
During the warm nights of July the Milky Way is at its best. The constellation of Scorpius lie to the south. It’s a wonderful area of the sky because it actually looks like a scorpion with a curved tail containing pinchers (also called “cats eyes”). Its brightest star, Antares, which is the beating red heart of the scorpion, is a red supergiant, one of the largest stars in the Milky Way galaxy, some 700 times larger than our sun. Its golden orange color can be enhanced and enjoyed by using binoculars. Just to the west of Antares is a globular cluster, M4, a mere 7200 light years from us. It is one of the most beautiful clusters to be seen in binoculars. Give it a try some evening. The area of Scorpius is full of star clouds and star clusters of the Milky Way, all of which will show up nicely in binoculars.
Further to the east of the scorpion is the constellation of Sagittarius, which becomes nicely visible in the early evening next month. It contains the center of the galaxy and even more brilliant star clouds and nebulae. Sagittarius is also the area of the sky where Pluto now resides. The New Horizons Spacecraft is heading toward Sagittarius, where it will rendezvous with Pluto next year.
Off to the west is where the action is taking place this month. In the constellation of Virgo, Mars is moving rapidly eastward toward its brightest star, Spica. Because Mars is our closest planetary neighbor beyond the earth, you can discern its movement with respect to the background stars, over a period of days. At the beginning of July it is well to the west of Spica, but on July 13, it achieves conjunction with Spica. It should be a great sight, blue-white Spica and yellow-orange Mars, practically colliding with each other.
The constellation of Scorpius
July 3: Earth is at its farthest distance from the sun, some 3.3% further than in January. If the axis of the earth were not tilted, this would be our winter season, all over the earth. But the tilt dominates and results in much more energy reaching the northern hemisphere on June than in December.
July 5: The half moon is very close to Mars and will actually cover it as seen from Hawaii and parts of Latin America.
July 7: Look for the moon close to Saturn tonight. In the southern part of South America the moon will cover Saturn.
July 13: Mars moves north of fainter Spica.
July 14: A year from now we will get our first close-up view of Pluto thanks to New Horizons spacecraft.
July 28: A modest meteor shower comes out of Aquarius for a few days around this date.
Pluto, the fascinating dwarf
On July 14, 2015, the Pluto system is due to be visited by a spacecraft from earth for the first time, when the New Horizons probe will fly within 6000 miles of the surface of the dwarf plant. The space craft, which was launched in January 2006, will be moving with a speed of 30,000 miles per hour. It now is only some 280 million miles away from Pluto, having already covered some 3 billion miles. When that magical moment of rendezvous arrives, can you imagine the incredible stress upon the astronomers who organized the mission?
Pluto was demoted to the status of a dwarf planet by a vote of astronomers at a meeting of the International Astronomical Union in Prague in 2006. In the interest of full disclosure, I was at the meeting and was among those who voted to demote Pluto. The fact that the New Horizons probe had been launched to Pluto just six months earlier played no role in this decision. Regardless of what we choose to call it, Pluto is still a very interesting object that had not yet been explored.
Pluto has five known moons: Charon, the largest, with a diameter about half that of Pluto, and tiny Nix, Hydra, Kerberos, and Styx. Because Pluto and Charon are so close in size and distance they can be considered a binary or double planet. The only other planet and moon in the solar system which could be a double planet are the Earth and our moon. The best explanation is that there was a colossal collision with another object some billions of years ago. In the case of the earth, a blob of semi-molten matter condensed to become our moon. In the case of Pluto, which is a mixture of rock and ice, much of that ice may have evaporated in the collision to become an object more rocky than Pluto. Our moon seems to be made of material very similar to the Earth’s crust and not like our more metallic interior. Mercury appears also to have suffered a major collision, which tore off its crust but didn’t result in a moon. Mercury is the only planet without a moon.
Charon and Pluto are also unusual in that each is tidally locked to the other. Charon always presents the same face to Pluto, and Pluto always presents the same face to Charon. From any point on the surface of Pluto facing Charon, the moon never moves from its position in the sky. On the other hemisphere of Pluto, Charon would never be visible.
Recent measurements have revealed that Pluto has a thin atmosphere of nitrogen, methane and carbon monoxide. Considering that its temperature of minus 229°C, it is surprising that it has any atmosphere at all. All of the gas should have frozen out years ago. Further adding to the mystery, it appears that gas may flow back and forth between Pluto and its moon. If this is confirmed, Pluto and Charon would be the first known example of a planet and moon that share a common atmosphere. The gas of its atmosphere could come from geysers on either Pluto or Charon or be the result of a recent comet impact. Only a dwarf and perhaps a jester, Pluto will have a good story to share next year.