by Kim Malville

Sky almanac

Mars and Saturn appear low in the western skies after sunset. Mars is moving eastward in the constellation of Libra toward Scorpio. Saturn is moving slowly eastward in Virgo. Jupiter rises in the late evening in Taurus. Brilliant Venus rises well before the sun and is about one-third of the way up in the eastern sky as the sky brightens. It lies between Gemini and Leo.

September 8: Look to the east about an hour before sunrise to see Jupiter above the moon.

September 12: Another treat for early risers: Venus, even brighter than Jupiter, will be close to the crescent waning moon.

September 19: In the fading twilight, about 45 minutes after sunset you can see the young crescent moon close to ruddy Mars.

September 22: Autumnal equinox occurs at 8:49am. This is when the sun crosses the celestial equator and the sun rises due east when viewed from an island on the equator.

Retrograde loop of Mars from October 2011 to July 2012. The center of the loop lies in Leo. 
photo by Tunc Teael an amateur astronomer in Turkey and a member of Astronomers without Borders.

The retrograde loop of Mars

This composite of images spaced some 5 to 7 days apart from late October 2011 (top right) through early July 2012 (bottom left), traces the last retrograde loop of Mars as viewed from Earth. These retrograde loops do not actually take place, but they are optical illusions that occur when the earth overtakes a planet and passes it, much like the illusion when your train is pulling out of the station and another train parked on a adjacent track appears to move backward. On March 4, 2012 Mars was opposite the Sun in Earth’s sky and closest to us. It is visible in the picture as the centermost and brightest image of Mars. This was also when the planet appeared to be moving backward (to the west) as its fastest apparent speed.

Curiosity lands on Mars

Curiosity descending beneath its parachute toward Mars. Photographed by the high resolution imager on the Mars Reconnaissance Orbiter. courtesy NASA

I stayed up until 11:31 to watch the whoops of joy by the folks at the Jet Propulsion Laboratory in Pasadena as Curiosity was lowered onto the surface of Mars by its flying crane. Without wishing to sound too jingoistic, it was a feat that only NASA could have accomplished. Russia has failed many times to reach Mars.  One thing I didn’t see that night was this photo taken by the Mars Orbiter showing Curiosity hanging below its huge white and orange parachute. The atmosphere of Mars is 100 times less dense that of Earth, so that it had to be a huge parachute, 70 feet in diameter.

The Mars Reconnaissance Orbiter was originally launched on Aug. 12, 2005. It arrived near Mars and has been orbiting the planet since March 2006. Its purpose was to document evidence for water on Mars. Now Curiosity is continuing the hunt for evidence of water on ancient Mars by studying the lower sedimentary layers of nearby Mount Sharp. Mount Sharp is only about 8 km away from Curiosity’s landing site as the crow flies. NASA says the rover will actually travel a few kilometers more because it will have to drive around obstacles. Curiosity can travel about 100 meters per day, meaning it will take about three months for the journey. Eventually working like a geologist with a rock hammer, Curiosity will climb upward, checking out each layer for water and past life.

An artist’s depiction of the central galaxy of the Phoenix Cluster. Hot gas is falling along ribbons into the galaxy and condensing into stars. courtesy NASA

The Phoenix cluster of galaxies

The visible universe is structured by gravity into three systems of increasing size:

• solar systems in which planets revolve around stars (there are more than a 1000 known solar systems in our galaxy);

• galaxies in which stars revolve around a center nucleus, which often is a immense black hole;

• and clusters of galaxies in which each galaxy revolves around a center of mass of the cluster.

Beyond clusters of galaxies, the attractive force of gravity loses out to the repulsive force of dark energy and because of that the universe will be accelerating outward for all future time.

Last month, on August 15, the largest cluster of galaxies yet discovered in the universe was announced with a great flurry of excitement. The paper is published in the journal Nature with many, many authors.  The cluster is known as the Phoenix, partly because it is in the constellation of Phoenix but, also, very symbolically, because new stars are being born out of its fires.  The cluster was first discovered in 2010 in Antarctica at the South Pole. Since then many telescopes have been used to study it.

Everything is immense about Phoenix. Here are the numbers:

2.5 Quadrillion: It is 2.5 quadrillion more massive than our own sun. That’s larger than our national debt! Astronomy reigns supreme (for a little while)!

3 Trillion: Number of stars in its central galaxy, compared to the 200 billion stars in our own Milky Way.

10 Billion: The black hole in its center contains the mass of at least 10 billion stars, perhaps making it the biggest black hole known in the universe. The black hole in the center of our own Milky Way galaxy contains a paltry 4 million solar masses.

5.7 Billion: Distance in light years. We are viewing it as it appeard 5.7 billion years ago.

740: Number of new stars created every year in the central galaxy of Phoenix, compared to one or two new stars formed in our own galaxy every year. Some of those new stars in Phoenix will be lost, falling in the black hole, making it more colossal year by year.

83: Number of authors of the paper announcing its discovery.