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  D e s e r t   E x p o s u r e   January 2009

Constellation of the Month: Fornax, the Furnace


Our constellation this month is another creation of French astronomer Nicolas Louis de Lacaille .In the early part of the 18th century, de Lacaille cataloged almost 10,000 stars in the far southern sky. The catalog was published posthumously in 1763 as Coelum Australe Stelliferum.

Fornax small map

Click the image for a larger map


Down in our southern sky shortly after sunset you can find the constellation of Fornax, the Furnace. There are no bright stars in this constellation, but Fornax contains a number of interesting, though faint galaxies. These include a nearby dwarf galaxy, the Fornax Cluster of Galaxies, and a very distant blue galaxy. The blue galaxy glows from the light of many young stars that have recently formed in it.

It organized the newly cataloged stars into 14 new constellations, which have since become accepted by the International Astronomical Union (IAU), the organization that decides all things astronomical. This grouping of stars in the southern part of our January sky was originally called Fornax Chemica, the "chemical furnace," supposedly a small solid-fuel heater used for heating chemical experiments.

The brightest stars in Fornax are fourth magnitude — led by Alpha Fornacis at an unspectacular magnitude 3.87 — so this constellation does not stand out in our evening sky. What this constellation does have is the Fornax Cluster of Galaxies. First recognized in 1943 by Harlow Shapley, the Fornax Cluster is the second-largest cluster of galaxies in our region of the universe, after the Virgo cluster. It covers about 40 square degrees in the southeastern end of Fornax, spreading into Eridanus. There are more than 300 galaxies in this cluster, which is about 53 million light-years away.

At the cluster's center is NGC (New General Catalog) 1399. From Earth, this elliptical galaxy is magnitude 9.4 and measures 6.9 by 6.5 minutes-of-arc across. But it is a gigantic galaxy, some 30 times the mass of our Milky Way. The larger galaxies are usually elliptical, rather than being spiral or barred-spiral like the Milky Way. The elliptical shape is attributed to the absorption of other nearby galaxies, pulled in by gravity. In fact, the heart of NGC 1399 is a black hole estimated to be 500 million times the mass of our Sun.

Another galaxy on its way to being an elliptical is NGC 1316, a lenticular galaxy that has some unusual dark dust bands across its glowing surface. These may be left over from NGC 1316's absorption of other galaxies: When a larger galaxy absorbs a smaller one, the individual packets of gas that made up the smaller galaxy become trapped in the larger one, but these packets continue to move at their original velocity — making them crash into other gas clouds much more frequently

All this extra gas floating around helps fuel the massive black hole at the center of NGC 1316. Not all of the gas that falls toward the black hole is pulled into it. For reasons we do not yet understand, some of the gas is shot out in two oppositely pointed, fast-moving jets, one from each pole of the spinning black hole. These jets, moving near the speed of light, squirt out of the galaxy, forming two large lobes on either side. As the jets knock off and accelerate electrons from the ambient gas, "synchrotron radiation" is generated and the electrons emit radio waves. These radio waves can be detected by radio telescopes here on Earth.

NGC 1316 is the fourth-strongest radio source in the sky. Since it is the brightest source in Fornax, it is designated Fornax A. When it was first detected, radio telescopes were too crude to carefully measure the location of the source in the sky, so radio astronomers used designations like Fornax A. Later, more refined radio telescopes could pinpoint the location of the radio source in the sky, allowing astronomers to associate the radio source with objects already cataloged from visual telescopes. So we now know that galaxy NGC 1316 is the same as radio source Fornax A.

The Planets for January 2009


Watch the Skies
(all times MST)

Jan. 4
4:56 a.m.— First Quarter Moon
7 a.m. — Mercury farthest east of the Sun (19 degrees)

Jan. 5
8 a.m. — Earth closest to
Sun for 2009

Jan. 10
8:27 p.m. — Full Moon

Jan. 14
2 p.m. — Venus farthest east
of the Sun (47 degrees)

Jan. 17
7:46 p.m. — Last Quarter Moon

Jan. 21
6 a.m. — Moon 0.3 degree
north of Antares

Jan. 26
12:55 a.m. — New Moon
(annular eclipse in the
south Indian Ocean)

As it gets dark, three planets will be low in our western sky. Mercury will move eastward (up) away from Jupiter. Brilliant Venus will be well above those two, almost as a guide to finding them in the bright twilight. The Messenger of the Gods passed Jupiter last month. They are both in Capricornus, and by Jan. 10, Mercury will stop moving eastward and head back west again. Midmonth will find both Jupiter and Mercury too close to the Sun to be visible. On Jan. 1, Mercury is 6.4 second-of-arc across and 67 percent illuminated at magnitude -0.6. It will get larger and more of a crescent as the month goes on. Meanwhile, Jupiter is 32.6 seconds-of-arc across, glowing at magnitude -2.0. It is a very poor telescopic target with a low altitude of only five degrees as it gets dark.

Venus starts the month in Aquarius and passes the bowl of Pisces by month's end. Venus at midmonth is 24.6 seconds-of-arc across and is exactly half illuminated. It will continue to get larger and become more of a crescent as the month goes on. Venus shines at magnitude -4.4 and sets around 9 p.m.

Saturn pops over the eastern horizon around 9:45 p.m. It stands still among the stars of southeastern Leo on Jan. 1, but over the next few months it will start moving westward again. Emitting its yellow glow at magnitude +0.9, Saturn is 18.9 seconds-of-arc across with the rings 42.8 seconds-of-arc across. The rings are still showing their southern face, but are tilted up only 1.0 degrees. This makes them look very thin, and they will soon be completely disappearing.

Mars is still too close to the Sun to be observed, but a year from now we will be observing a reasonably good opposition, so start thinking about what you would like to see on the Red Planet, and "keep watching the sky"!

An amateur astronomer for more than 35 years,
Bert Stevens is co-director of Desert Moon Observatory in Las Cruces.


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