This month’s star chart shows the southern sky at 10:00 PM on June 13,
the night of the new moon. Mars is well placed about 45 deg above
the horizon, halfway to the zenith, shining at mag -0.8 (remember, negative
mags are brighter than positive ones). Mars reached opposition on
April 24, when its disk subtended about 16 arcseconds. Tonight its
apparent diameter is about 13 arcsec. Near its closest opposition
Mars subtends about 25 arcsec, so on occasion it offers nearly twice as
large an image as we see at this time.
Scorpius, our most prominent southern constellation, is now rearing his
head above the horizon near the beginning of evening twilight. I’ve
always liked Scorpius because it’s one of the few constellations that really
resemble what they’re supposed to be. As spring gives way to summer,
more and more of the creature’s body will become visible. Eventually
the recurving tail will rise well above the horizon in early evening.
The red giant Antares, sometimes called the Heart of the Scorpion, is the
prominent star in the body. Antares varies in brightness from about
mag 0.86 to 1.06. Located about 520 LY away, Antares is about 600
million miles in diameter – larger than the orbit of Mars. If Antares
changed places with the sun, then where would the earth be?
Omega Centauri, a little east of south, is another of the glories of the
southern sky this time of year. Located 17,000 LY away, this is the
largest globular in the sky. >From a good location, this globular
is visible to the naked eye as a fuzzy “star” about 9 deg above the horizon.
It is readily visible in binoculars and a fine object in a telescope.
The cluster is about 300 LY in diameter and has about 1 million stars.
The globular clusters form a roughly spherical halo around the disk of
our Milky Galaxy. It is possible that Omega Centauri and some of
the other large globular clusters may be the remnants of the cores of
other galaxies torn apart by the gravity of the Milky Way.
In the central part of Omega Centauri, the stars are only about 1/10 LY
apart, compared with the distance of about 4 LY from the earth to the nearest
star, after the sun. If there are any planets in the middle of a
big globular cluster, there may never be any night. Do you suppose
the Omega Centaurians, if there are any, ever get any sleep?
You can print a copy of this star
chart so you can take it outside.
