akersfield Night Sky – March 3, 2012
By Nick Strobel
This month's sold-out evening show "Black Holes" explores the two basic types of the ultra-compact objects: stellar-mass black holes that form at the cores of dying massive stars and the supermassive ones that are hundreds of thousands to billions of times the mass of the Sun and reside at the centers of galaxies. Astronomers are beginning to find some black holes with intermediate masses that "bridge the gap" between the two groups. A stellar-mass black holes forms when a star with a mass at least 25 times the mass of the Sun dies. The core of the star collapses and the shockwave from the collapse blasts the outer layers of the star outward in a huge explosion called a supernova. Only the big stars do this—the more common lower-mass stars like our Sun do not die this way. Stars like our Sun will end their lives with a much gentler death where the outer layers puff outward to form what's called a planetary nebula and the core forms a dense object called a white dwarf.
In typical celebrity-worship fashion, the popular media focuses on the flashy rare deaths of stars born with a lot of material (bling) and ignores all of the common calmer deaths of ordinary smaller stars. Sigh! However, I have to admit that I am one of "them" and I'm just as fascinated with those flashy deaths as the next person (uh...star deaths that is). The really big black holes are cool too, though actually they can be quite hot astronomically speaking as gas spiralling into them forms a disk of super-hot material heated by the friction of the disk material bumping against other material in the disk. Our galaxy, the Milky Way, has a supermassive black hole at its center with a mass of about 4 million or so times the mass of our Sun. Though that might seem like a pretty hefty beast, it is small compared to most other supermassive black holes we have discovered so far and certainly very small compared to the mass of the rest of the Milky Way. The Milky Way is at least hundreds of times more massive than the supermassive black hole at its core so even if the super-massive black hole was not there, the stars of the Milky Way would still orbit pretty much as they do now because of their mutual gravity pulling on each other. You can find out more about black holes, including how we find them by going to my free online textbook at www.astronomynotes.com (just enter "black hole" in the search field).
Right here on Earth we have some cool things to look at in our sky too. The brilliant pair of planets, Venus and Jupiter, in the southwest evening sky continue to close on each other as shown in the first chart below. Tonight they are slightly less than a fist-width at arms length apart from each other. Between March 12th and March 14th, they will be about the same distance apart on our sky as your knuckles when seen at arm's length (see the inset of the first star chart below). After mid-March Jupiter will slowly fade as the Sun catches up to it (or rather, as the Earth moves to the opposite side of its orbit behind the Sun with respect to Jupiter). Venus will continue to climb up away from the Sun until March 26th after which Venus will head back toward the Sun, crossing the Sun's disk on June 5th (the last such crossing or "transit" for 105 years). This evening after sunset also try to spot Mercury low in the west. It is a little more than a spread-out hand width (pinky tip to thumb tip) at arm's length below and slightly to the right of Venus. Tomorrow evening marks its greatest separation from the Sun on our sky and after that it will quickly plunge back toward the Sun, lost in the twilight glow by mid-March.
The Waxing Gibbous Moon will be visible starting in the afternoon today and will be high up in the southeast with the stars of Gemini at sunset. A little over a week ago the thin Waxing Crescent Moon was between Venus and Jupiter, a gorgeous sight. I managed to get a couple of good pictures. A month later near the end of March, the Moon will give a repeat performance as a thin crescent between the two planets but their positions will be reversed with Venus above Jupiter.
Tonight Mars is directly opposite the Sun on our sky so it will be rising as the Sun is setting. Mars will be closest to the Earth on Monday, March 5th. Mars is moving swiftly backward just under the stars of Leo toward Regulus at the end of the Sickle. The Full Moon will pass south of Mars on the night of March 7th and three nights later the Waning Gibbous Moon will slide south of Saturn—see the second chart below. The Moon will be at Third Quarter phase on the evening of March 14th. Saturn becomes visible in the east at about 9:45 PM tonight. Saturn is also moving backward (retrograde) toward the brightest star of Virgo, Spica, but its retrograde loop is much smaller than Mars' because of its much larger distance from us. The planets farther from Earth have less noticeable retrograde loops for the same reason your thumb appears to have a smaller shift when you hold it at arm's length and look at it with one eye and then the other eye as compared to when you hold your thumb just beyond your nose. Saturn will be up highest due South at about 3 AM. The third chart below shows pre-dawn sky at 5:30 AM.
Next Saturday evening, don't forget to move your clocks forward an hour for the start of daylight-savings time. The appearance of Leo in our early evening sky and the "springing" forward of our clocks tells us that spring is on its way. The official beginning of spring happens on the night of March 19th when the Sun crosses the Celestial Equator heading northward toward the June solstice. The Celestial Equator is the projection of the Earth's equator onto the sky, splitting the sky into north and south halves.
Want to see more of the stars at night and save energy? Shield your lights so that the light only goes down toward the ground. See www.darksky.org for how.
Director of the William M Thomas Planetarium at Bakersfield College
Author of the award-winning website www.astronomynotes.com