By Andy Veh, for the Redoubt Reporter
Compared to September, the scene in the night sky has shifted somewhat toward the east, with Bootes setting in the northeast. Its brightest star, Arcturus, can be seen in the early evening on the northeastern horizon.
Prominent constellations and stars this month are the Big Dipper low in the sky, and the Little Dipper (part of Ursa Major) high in the north, Cygnus with Deneb, Lyra with Vega, and Aquila with Altair still high in the west. These three stars form the summer triangle. It’s perhaps comforting in Alaska that we can see this summer triangle all winter along, albeit on the horizon.
Cassiopeia appears overhead, near the zenith, and Pegasus’ square/diamond is high in the south. Very late in the evening Orion rises with Betelgeuse and Rigel in the east, following Taurus with Aldebaran and the Pleiades star cluster.
Mercury, Venus and Saturn are not visible this month because they are setting and rising at about the same time as the sun.
Jupiter rises in the east between 10 and 11 p.m. Due to its glaring brightness, you can’t miss it. Jupiter will be visible during the late evening and into dawn all month and all evening during the entire winter. The third quarter moon joins the giant planet Oct. 24 and 25.
Mars rises in the east around 2 a.m. The moon’s waning crescent joins the red planet Oct. 1 and Oct. 29. The most exciting pairing, though, is that of Mars and Leo’s Regulus on and around Oct. 15, as Mars passed the star within just one degree. Both of them are equally bright as seen from Earth, though Mars, at 200 million miles, is much closer than the star, at 450 trillion miles. Thus, Regulus being a star is truly much, much brighter than the planet, as Mars is just reflecting our star’s (i.e. the sun’s) light. Furthermore, during October, Mars is moving right to left past Regulus, and through its constellation Leo, the lion, mostly near its front paw. That shows that planets indeed move — and that’s what the name planet means, a “wanderer.”
If you’re an early riser and look south at any time before dawn, you will see, from west to east, red Aldebaran in Taurus, bright Jupiter, then Mars and/or Regulus in Leo.
Uranus and Neptune are still visible. The best way of finding them is using a finder chart (such as in the February issue of Sky & Telescope, http://media.skyandtelescope.com/documents/Uranus-Neptune-2013.pdf), then to star hop with stable binoculars (I recommend propping your elbows on a car’s roof).
This month’s issue of Astronomy magazine contains a cover story about the “top 10 exoplanets.” The top-10 list includes the closest (four light years), fastest (600,000 mph, a six-hour orbit), hottest (12,500 degrees Fahrenheit), least massive (0.44 Warth masses), oldest (13 billion years) planets, and the ones with the longest orbit (900 years), with most planets (three) in the habitable zone, the planet with the most host stars (four), a planet with possible layers of diamond and graphite, and planets orbiting pulsars (they apparently survived the supernova explosions).
Until about 1992, only nine planets had been known — the ones in our solar system. Twenty years ago detection methods had become so sensitive that, in our galaxy, planets orbiting other stars could be discovered.
The most prominent method uses the Doppler effect (which is also popular among law enforcement to catch speeders) — the spectral lines of a star shift to a higher or lower frequency when that star is approaching or receding. It would do so periodically if a planet orbiting it kept tugging at it. (Radar speed guns use the frequency shift of micro- or radiowaves to compute a vehicle’s speed.)
The star’s velocity, computed from the frequency shift, combined with the period of its wobble yields the minimum mass of the orbiting planet. The more massive that planet is, the better the effect shows up, hence most exoplanets discovered so far are the size of Jupiter or Saturn.
As of Monday, 997 extrasolar planets have been discovered. At the current rate there should be newspaper headlines around Sept. 29 announcing the 1,000th.
For lots more data, check exoplanet.eu.
Andy Veh is an associate professor of physics, math and astronomy at Kenai Peninsula College.