Greetings stargazers.
This has been an eventful month. From my backyard I got to see an aurora and a comet with my naked eyes. Yes, the camera showed both of those much more clearly, but it was fun seeing these rare events without assistance.
I have seen several bright comets, but Tsuchinshan-ATLAS had by far the longest tail I have seen unaided. If you missed seeing it, you will have another chance in about 80,000 years. That makes it one of the long-period comets from the Oort cloud, rather than a short-period comet from the Keiper belt.
The solar system is filled with small objects that are leftovers from its formation. These leftovers are the objects that were lucky enough to be in orbits that didn’t cross too near a planet that could pull them in for a collision or deflect their trajectories into the sun. If their stable orbits were inside that of Jupiter, they were close enough to the sun to be heated so all the very light, or volatile molecules, such as water or carbon dioxide were evaporated leaving a rocky shell behind. These are the asteroids.
If the orbits of the debris are farther away from the sun, then their volatile materials stay frozen to the surface. Likely most of the mass of the more distant objects consists of lighter materials, so the description of them as dirty snowballs is quite appropriate.
If their orbits happen to get deflected by some slight gravitational tug from a planet or other piece of solar system debris, they may head toward the sun. Once they are close enough to the sun to be heated, the volatile materials evaporate, and the released clouds that are lit up by the sun are what we recognize as comets.
About half all comets are from the region known as the Keiper belt. This is a disk aligned with the solar system (but not quite as flat) that lies beyond the orbit of Neptune. The most famous Keiper belt object is the dwarf planet Pluto. If Pluto was somehow deflected toward the inner solar system, there is a good chance it would develop quite a tail. Comets that originate in this part of the solar system have periods that are measured in decades rather than millennia and are seen multiple times. Halley’s comet is the most famous of this type.
The other repository of comets is called the Oort cloud. This vast cloud is thousands of times more distant and much more spherical than the Keiper belt. Objects there are only very loosely bound to the sun, and the only evidence we have of its existence is that we regularly get very long-period comets such as Tsuchinshan-ATLAS.
Comet Tsuchinshan-ATLAS is leaving the inner solar system but should be visible through binoculars or telescopes for a few more weeks.
Venus keeps getting higher every night as the evening star and will be in the southwestern sky after sunset for the next few months.
Saturn is visible in the southern evening sky and is approaching the time when its rings will be edge-on as viewed from Earth. This happens every fourteen years or so, and in March of next year it will appear to be just another ringless disk in a telescope. Maybe like a smaller, dimmer version of Jupiter.
Jupiter is rising in the East soon after sunset and will reach opposition, its closest approach to Earth in early December. The four Galilean moons are always a fun binocular target.
All year we have been waiting for the expected nova outburst of T Coronae Borealis, the Blaze Star, but the constellation is setting before 8:00 now. Maybe it will hold off on exploding until it comes out from behind the sun again in the morning sky early next year.
The sun is still very active, so there could be more aurora visible here at any time.
Useful links
Comet Tsuchinshan-ATLAS
https://www.astronomy.com/observing/comet-tsuchinshan-atlas-will-soon-move-into-the-evening-sky/
Keiper Belt
https://en.wikipedia.org/wiki/Kuiper_belt
Oort Cloud
https://en.wikipedia.org/wiki/Oort_cloud
Astronomy picture of the day
http://apod.nasa.gov/apod/
An Astronomer’s forecast for Durango
http://www.cleardarksky.com/c/DrngoCOkey.html?1
Old Fort Lewis Observatory
http://www.fortlewis.edu/observatory
hakes_c@fortlewis.edu
Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory.
