Night Sky Highlights for October-December, 2015
Solar System
Mercury
The innermost planet will be visible in the east before dawn in mid-October, with the best views around October 16. It will be in the western sky just after sunset in late December, with the best views around December 29.
Venus
Throughout the fall, Venus will be shining brightly in the eastern sky before dawn. Its greatest western elongation, when it will be highest in the sky, is on October 26, but it will be readily visible through the rest of 2015 and into the beginning of 2016. During the morning of December 7 (in daylight), the crescent Moon will occult Venus. This could be interesting to watch with binoculars or a telescope (as always, being very careful not to point your telescope anywhere near the Sun!).
Mars
This is not a good year for observing Mars because it is far from the Earth, but it can be seen in the pre-dawn sky this fall, with the best views in December when it is highest in the sky.
Jupiter
Along with Venus and Mars, Jupiter will also be visible in the early morning hours throughout the fall, located in the tail end of Leo, the Lion. By December, it starts to rise before midnight, so it can be viewed very late in the evening.
Saturn
The ringed planet is in Scorpius, and it will still be observable during October low in the southwest sky just after sunset. After that, it will start to disappear in the glow of the western sky at dusk, and it will not be visible for the rest of 2015.
Uranus and Neptune
After Saturn disappears from view in early November, none of the bright planets will be visible in the evening sky, so this fall is the perfect time for viewing Uranus and Neptune, especially if you have never seen them through a telescope. They can be a challenge to find and observe, but a challenge that can be accomplished with a little effort. Both can be viewed in even small telescopes or binoculars if you have a chart showing you where to look. These planets move very slowly against the background stars, so once you have learned to locate them, you can show these outer planets to your friends or to fellow astronomy enthusiasts at a later time. For many people, this will be the first time they have seen these outer planets in the night sky.
Both Uranus and Neptune have a blue or green tint that helps to distinguish them from stars in the vicinity. Once you locate them, use high power to view their small disks. With large telescopes, some of the moons of Uranus can be dimly seen, and so can Triton, the largest moon of Neptune.
Uranus is in Pisces and Neptune is in Aquarius. These finder charts from Sky & Telescope can be used to locate them:
http://www.skyandtelescope.com/wp-content/uploads/WEB_UrNep_Finders.pdf
Geminid Meteor shower
Peaking on December 13-14
It should be a good year for the Geminids because they reach maximum around the time of the new Moon. This is a very strong and reliable meteor shower, and at its peak, from 50 to over 100 meteors per hour can be seen under ideal conditions. The best time to watch in in the early morning hours, but these meteors can be seen in the mid to late evening as well.
Deep Sky Objects
Every deep-sky object on this list for the fall season can be seen with the naked eye under some conditions, although they vary from very easily visible objects to those that are so dim that they require very dark skies and good eyesight. Of course, most of them are a much better sight in binoculars or a telescope.
Star Clusters and Associations
Perseus Double Cluster
Pair of open clusters in Perseus
With the naked eye, these two clusters appear as a faint oblong cloud. Through a telescope, hundreds of stars can be seen, including several red giant stars (which have an orange-red tint). This is almost certainly the most impressive pair of open clusters in the night sky.
Alpha Perseus Association
Stellar association in Perseus
Find the brightest star in Perseus, and look closely around it with the naked eye. You should see a number of dimmer stars in the vicinity. These are hot, blue-white stars in a loose group or association. This group is also called the Perseus OB1 Association because the spectral classification of these stars are O and B. This is a good target for binoculars; the group is too large to view well through a telescope.
Messier 45, the Pleiades
Open cluster in Taurus
This group is also known as the Seven Sisters, and it is probably the best-known star cluster. An observer with good eyesight can see seven or more stars under good conditions. Even under light polluted skies, about five stars can be seen in a tiny dipper shape. This is a great object for binoculars or a telescope with a wide-angle eyepiece.
The Hyades
Open cluster in Taurus
This cluster appears large because it is relatively close to us, at about 150 light years. The reddish first-magnitude Aldebaran marks the location of this cluster, but Aldebaran is actually closer to us and not part of the group. Several of the other brightest stars form a V-shape that represents the head of Taurus, the Bull.
Galaxies
The Milky Way
Portions of our home galaxy can be seen throughout the fall. In October, look for the bright sections of the Milky Way in the southwest in the constellations Sagittarius, Scutum, and Aquila. Later in the fall, look in Cygnus, Cassiopeia and Perseus.
Messier 31, the Andromeda Galaxy
Spiral galaxy in Andromeda
The nearest spiral galaxy to our own is fairly easy to see with the naked eye on a dark clear night. We have seen it and pointed it out to visitors many times at public observing sessions at Young’s Pond Park in Branford. Through a telescope, its two largest satellite galaxies (M32 and M101) can also be seen.
Messier 33, the Triangulum Galaxy
Spiral galaxy in Triangulum
This is the most difficult object on this list to observe with the naked eye, and it may not be possible from the light-polluted skies of Connecticut. However, at magnitude 5.7, M33 is bright enough to see under very dark skies, and many observers have seen without optical aid. It should look like a very diffuse glow about the size of the Moon. Since it is a bit farther away than the Andromeda Galaxy, for most people it is the most distant object visible to the naked eye. (But there are exceptions, and some expert observers with very good eyesight have seen more distant galaxies.)
Variable and Multiple Stars
Algol (Beta Persei)
Variable star in Perseus
Algol is an eclipsing binary star, and it has been known to be variable since ancient times. Normally it is magnitude 2.1, the second brightest star in Perseus. But the dimmer of the two stars eclipses the brighter every 2.85 days, and for about 10 hours Algol’s brightness decreases, dropping to magnitude 3.4 at its minimum.
Algiedi (Alpha Capricorni)
Double star in Capricornus
Look closely at the star at the western tip of Capricornus, and you should be able to detect that it is a double star. The two components are separated by about 1/10 degree (or about 1/5 the diameter of the full Moon). This is an optical double–a chance alignment of two stars that are not really close together.
Omicron 1 Cygni
Triple star in Cygnus
This multiple star system, about 5 degrees to the west of first-magnitude Deneb, is well worth checking out. With the naked eye you might be able to detect that it is a double star if you have good eyesight, but it is not easy. It is just about one degree from a similarly bright star, Omicron 2. But in binoculars or a telescope, three stars of different colors can be seen. The brightest is yellow or orange, and next to it is a dimmer blue star. On the opposite side, a little farther away, is the third component, mainly white. This is a very attractive group through a low power eyepiece.