The November Meteors, Chromolithograph by Étienne Léopold
The November Meteors, Chromolithograph by Étienne Léopold Trouvelot, 1868

This Week’s Sky: November 17 to 23

Leo’s meteors, neighbourly M31 and double Gammas

November 18

From midnight to dawn, the annual Leonid meteor shower reaches its peak with a predicted Zenithal Hourly Rate (ZHR) of some 15 meteors per hour. Although the shower competes with a gibbous Moon this year, the Leonids are still worth a look.

In 1833, this event turned into a storm of 100,000 meteors per hour. Another major storm occurred in 1966. In recent years, Jupiter seems to have changed the orientation of the debris trail of Comet Tempel-Tuttle, the Leonids’ source, so the latest storms happened back in 1999 and 2002.

November 19 to 23, 9 p.m.

For naked-eye and binocular observing, mid-week evenings provide Moon-free views of our nearest spiral galaxy neighbour. From a reasonably dark-sky site, Messier 31, the Andromeda Galaxy, presents to the naked eye as a hazy dash of light directly overhead. Look for it atop a stack of three modestly bright stars in Andromeda. Start with second-magnitude Beta Andromedae, also called Mirach. Look above that to Mu Andromedae, then above Mu to Nu Andromedae. Directly above Nu, M31 shows as a fuzzy, elongated slant of light of magnitude +3.4. From a very dark site, M31 may appear 0.5 degree across, about as wide on the sky as our Moon. Telescopic observers can see M32 and M110, M31’s elliptical satellite galaxies.

While you’re looking up, consider how the Andromeda Galaxy is 2.5 million light-years away. In 1925, astronomer Edwin Hubble was the first to resolve its variable stars, using Mt. Wilson’s 2.5-metre telescope to prove M31 is a gigantic galaxy like ours. Remember, too, our Milky Way galaxy and M31 are “rushing” toward a collision with each other—in about three billion years!

All Week, 11 p.m.

After last week’s transit and lunar activity, telescope users can enjoy the quiet sight of some fine double stars in the constellations Andromeda and Aries.

Gamma Andromedae, also called Almaak, is an excellent example of contrasting colours within a binary star system. Like Albireo of our summer nights, Gamma And’s two main components shine orange and blue. The fainter blue component is itself a binary, but at magnitude +5.0, splitting this close pair may not be easy even at high magnification. The brighter star is a K-type giant of magnitude +2.3. The pair’s contrast shows us how a star’s colour is dependent on its surface temperature. The orange-tinted star is really the cooler of the two, while the bluish component radiates hotter and more energetically. Our star’s temperature is roughly between the two, so the Sun shines with a moderate, white light.

Just below Almaak is Gamma Arietis, also called Mesarthim. This binary features blue-white components shining at +4.6 and +4.7—an almost evenly matched pair of hot, A-type stars. Astronomer Robert Hooke was the first to describe this double in 1664. Can your eye tell which of the two is brightest?