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(Pronunciation: Se - fee - us) On cool September
nights, shift your attention to the north. If your skies are dark and
moonless you can see the Milky Way, which runs diagonally through this
map. To find this month's target constellation, use the familiar W-shape
of Cassiopeia, then find Polaris, the North Star. Finally, locate bright
Deneb in the northwest. Right smack in the middle of the large triangle
you made lies Cepheus, the King.
Cepheus is a constellation that originates in Greek mythology. The King plays a small role in the story of Perseus the Hero, Andromeda the Maiden, and Cassiopeia the Queen. Cass boasted that she and her daughters were more beautiful than the Nereids, or Sea Nymphs, which were the daughters of Poseidon (or Neptune). When Poseidon heard about it he wasn't happy, and sent floods to punish vain Cassiopeia. Then, good old Cepheus consulted an oracle, who told him the only way out of the jam was to sacrifice one of his daughters. (Aren't you glad Cepheus wasn't your dad?) So poor Andromeda was chained to a rock as a snack for Cetus the sea monster, but she was saved by Perseus, the son of Zeus. (Credit for this info: Chris Dolan's Stars and Constellations webpage.
Modern stargazers see Cepheus as a house with a really steep roof, or as the traditional throne (which in the above map is upside down) that Cepheus occupies.
In this larger, more detailed view, (adapted from Norton's Sky Atlas 2000.0), we'll take a closer look at some of the interesting sights in Sagittarius. Our tour goes in order of Right Ascension, which is right to left on this map. The symbols below show how an object is best viewed:
with your naked eye;
with binoculars,
and
with a telescope.
NGC 6939.
One half of a pairing of very different objects, this open cluster
is dense, rich, and contains about 80 stars.
NGC 6946. The
other half of the pair is this face-on spiral galaxy. At magnitude 8.9,
it sounds fairly bright, but its brightness is spread over a large
area, so it will appear faint in medium sized (6 to 10 inch) scopes. More
info on NGC 6946.
IC 1396. You
haven't seen that "IC" in Constellation of the Month before. It stands
for Index Catalog, an appendix to Dreyer's original NGC Catalog. IC 1396
is a combination of open cluster and diffuse nebula. The nebulosity only
shows up well on photos, while the cluster is large and loose, embedded
in the Milky Way. More
on IC 1396.
NGC 7235.
Another open cluster, in between Epsilon (e)
and Zeta (z) Cephei. This cluster is small,
dense, and well defined.
NGC 40. An unusual
red planetary nebula with an 11.6 magnitude central star. This object is
a challenge for small to medium sized scopes.
Double and Variable Stars
Mu (m) Cephei. The "Garnet Star". This
is one of the most beautiful, and most reddish colored stars in the sky.
Delta (d) Cephei. Another famous star,
which has a whole class of stars named after it. Delta is giant yellow
white "variable" star that swells and contracts with time. It has a regular
period of 5 1/2 days. If you observe Delta with a telescope over several
consecutive nights and compare its brightness to the stars nearby it, you
can easily see the change in brightness. "Cepheid variables" are remarkably
constant all over the universe, and have played a key role in determining
the distances to other galaxies
Omicron (o) Cephei. This double star's
components are magnitudes 4.9 and 7.1, respectively. They are also very
close together, separated by only 2.8 arcseconds. This double is a test
for your telescope's optics!