August 25, 2013

What's Up in September: Signs of a season changing in the night sky

By BERNIE REIM

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Nova Delphini is already fading again, but it will be very interesting to keep watching it to see how rapidly it will fade. I was lucky to first see this nova just hours after it first exploded. It was a faint, 17th magnitude star in Delphinius the Dolphin that suddenly became 100,000 times brighter. It reached its brightest magnitude of 4.2 on Aug. 16. This is called a recurrent nova and the mechanism that causes its sudden outburst is fascinating. It consists of a white dwarf, which is what our sun will turn into in 5 billion years, along with another star in that binary system that has hydrogen gas spiraling onto the surface of the white dwarf. As this gas gets thicker and denser on the surface of the white dwarf star, it will suddenly explode in a runaway hydrogen fusion reaction. It will then expel this thin, earth-sized shell of a hydrogen bomb, leaving the white dwarf intact. This could happen many times with a period of tens of years up to tens of thousands of years.

In the extreme case, if a red giant is spiraling vast amounts of hydrogen gas onto the very dense surface of a white dwarf, it will completely blow apart both stars as it reaches a critical mass of 1.44 solar masses, also called the Chandrasekhar limit after the astronomer from India who first discovered the laws governing this phenomenon. This is called a Type 1A supernova. It always explodes at exactly that mass, so it can be used to accurately determine distances to far away galaxies in our universe. Thousands of Type 1A supernovae were recently used to figure out that our entire universe is expanding at an ever-increasing rate.

I recently attended the Stellafane astronomy convention in Springfield, Vt. This is an annual pilgrimage for thousands of amateur astronomers. They always have great practical workshops and excellent speakers to further inspire everyone's interest in astronomy, which is really obtaining that greater cosmic perspective that we all need to better understand where we are in space and even to understand what is actually happening right here on Earth.

The Milky Way was just incredible over Breezy Hill at 1,300 feet above sea level. I could easily see thousands more stars than I can usually see even from a good location in southern Maine. It seemed to engulf the entire scene in its great beauty and energy. Everyone needs to really experience a wonderful dark sky like this more often to better appreciate our connection to it and how all these stars directly provide for our lives.

We also saw a dozen or so good Perseid meteors from that fantastic location. Around 2 a.m., one brilliant and memorable meteor created a twisted trail that seemed to pulsate in the sky for a few seconds before it faded out and the night once again returned to its native blackness.

SEPTEMBER HIGHLIGHTS

Sept. 3. On this day in 1976, Viking 2 landed on Mars.

Sept. 5. New moon is at 7:36 a.m. Voyager 1 was launched on this day in 1977.

Sept. 8. The moon passes less than half a degree below Venus this evening.

Sept. 9. The moon passes just south of Saturn this evening.

Sept. 12. First quarter moon is at 1:08 p.m.

Sept. 15. The moon is at perigee -- its closest to Earth -- at 228,286 miles today.

Sept. 18. On this day in 1977, Voyager 1 took a photo of Earth and the moon from deep space.

Sept. 19. Full moon is at 7:13 a.m. This is also called the Harvest Moon. It will rise only about half an hour later each night instead of the usual 55 minutes later, due to the shallow angle of the ecliptic to our horizon at this time of year in the evening sky in this hemisphere.

Sept. 22. Pioneer 10 left the solar system on this day in 1990. Fall starts at 4:44 p.m.

Sept. 23. On this day in 1846, J.G. Galle discovered Neptune.

Sept. 26. Last quarter moon is at 11:55 p.m.

Sept. 27. The moon is at apogee -- its farthest from Earth -- today at 251,225 miles.

Sept. 28. The moon passes 5 degrees south of Jupiter this morning at 5 a.m.

Bernie Reim of Wells is co-director of the Astronomical Society of Northern New England.

 

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