Bakersfield Night Sky – April 18, 2015
By Nick Strobel
Well, the tax returns are now all done, so we can now relax under a starry sky and enjoy the sights. April is Global Astronomy Month and one of the ways to participate is Globe at Night. This program is an international citizen-science campaign to measure the night sky brightness from all over the globe and, in the process, raise public awareness of the impact of light pollution.
This month you can use the constellation Leo to determine how dark is our sky. Go outside more than a hour after sunset (so tonight, observe after 8:45 PM). Make sure the Moon is not up and give your eyes about ten minutes or so to get used to the dark. Match your observation of Leo with one of the star brightness (magnitude) charts on the Globe at Night website (www.globeatnight.org) and note the amount of cloud cover. The "Report" link on the website will automatically enter the date, time, and location of your observation if you allow it to use the location feature of your computer, tablet or phone.
An easy way to locate Leo is to use the Big Dipper part of Ursa Major. The Big Dipper is always somewhere in the northern sky and the asterism is bright enough to see even from most of Bakersfield. The star chart below shows the Big Dipper and Leo. The two end stars in the bowl part of the Big Dipper will point to the North Star, Polaris. Going in the opposite direction, those pointer stars will point you to the middle of Leo.
Look for a backward question mark on the sky. (It was known as "the Sickle" in past decades.) That is the head and chest part of the Lion. The bright star, Regulus, is at the bottom of the question mark, so perhaps it is the heart of the lion. The name means "the little king". Regulus is a blue-white star only 79 light years away. The star is near the end of its healthy adult stage of its life, fusing hydrogen to make helium in its core.
Regulus shines with a luminosity of about 360 times the Sun and it has a mass about 3.4 times the Sun. Because its mass is more than the Sun, it will have a shorter life than the Sun. The more massive stars are the gas-guzzling SUVs of the cosmos. Regulus is roughly 250 million years old, much shorter than the 4.6 billion year age of the Sun and much less than the 10 billion year lifetime of the Sun.
Regulus is actually a quadruple star. The easiest-to-see companion orbits the main star at about 100 times the distance that Pluto orbits the Sun with a period of at least 125,000 years. That companion is actually a double-star system! Those stars orbit each other from a distance of a little over twice Pluto's distance from the Sun. Both stars are smaller and dimmer than the Sun, one an orange-warm star and the other a cooler red star.
The fourth star of the system orbits very close to Regulus in a time of just 40 days. It appears to be a white dwarf, the dead remains of a star that used to be slightly more massive than the main star. We know it once was more massive than Regulus because more massive stars live shorter lives than lower mass stars and the former star very, very likely formed at the same time as Regulus. When the former star went through its dying red giant phase, it dumped gas onto Regulus which is why Regulus is spinning so fast today and is also why the white dwarf has such an unusually low mass, just 30% of the Sun.
In the middle of the question mark (Sickle) part of Leo is Algieba, a double giant with at least one planet orbiting the brighter giant. The giants are 131 light years away and orbit each other at an average distance of more than four times the distance between Pluto and the Sun. The two stars are in the dying stages of their lives having bloated outward to diameters of 29 and 12 times the diameter of the Sun. They have masses of 3.0 and 2.5 times the mass of the Sun.
To the left of the question mark (Sickle) part of Leo is a triangle of brighter stars. The top right star of the triangle is Zosma which means "girdle" and it is at the hip of the lion. Zosma is only 58 light years away and has a luminosity of 23 times the Sun. It has 2.2 times the mass of the Sun and it is over halfway through its billion-year long lifespan.
The far left star of Leo is Denebola, which appropriately means "tail of the lion". Denebola is a white-hot star just 36 light years away. It is in its healthy adult stage fusing hydrogen in its core. Denebola has a luminosity of 14 times the Sun and is surrounded by a dusty disk that could be forming planets.
Another easy way to find Leo that will work for the next several months is to look for Jupiter high up in the southern sky at 9 PM. Jupiter shines brighter than any star in the night sky, so you'll have no trouble finding it. Leo will be to the left of Jupiter. To the right of Jupiter, see if you can spot the Beehive Cluster at the heart of the dim zodiac constellation, Cancer. Jupiter had almost reached the Beehive Cluster when Jupiter was doing its retrograde motion earlier this year but now Jupiter is moving toward Leo, reaching Regulus in August. "Reaching Regulus" is not literal, of course, since Jupiter is about 1.25 million times closer to us than Regulus.
The next couple of nights will be good nights for the Globe at Night observations (depending on the weather) because the Moon is at New Phase today. Tomorrow the very thin Waxing Crescent will already have set by the time the sky is dark enough for the observations. The First Quarter Moon will pass beneath the Beehive Cluster on April 25th.
Further west you'll spot the only planet that outshines Jupiter, our nearest neighbor, Venus. Venus is now at the head of Taurus and by the end of the month you'll see it at the tip of the horns.
Another thing to do in this coming week of Astronomy month is to enter your ideas for names of features on Pluto and its moon Charon. Go to www.ourpluto.org to submit your suggestions and to vote for your favorites. The ballot will close on Friday, the 24th. On July 14th, the New Horizons spacecraft will fly past Pluto and Charon, snapping pictures and madly taking hundreds of measurements as it flies past at 31,300 mph.
Right now, Pluto is just a fuzzy blob in New Horizon's cameras but the New Horizons team wants to have a ready list of names to give the craters, cracks, cliffs, plains, etc. that will be visible by the end of June. New Horizons will be the first spacecraft to get to Pluto. NASA launched New Horizons on its fastest rocket nine years ago. It reached the orbit of the Moon in just nine hours. If there had been a delay in its launch, it would not have been able to swing by Jupiter to get a gravity boost that shaved six years off its journey.
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