Bakersfield Night Sky – April 4, 2015
By Nick Strobel
Tomorrow is Easter and the end of our spring break. Easter happens on the first Sunday after the Paschal Full Moon for that year which is usually the full moon as astronomers determine it after March 20th. The calculations are based on observations from Jerusalem instead of from Greenwich. The Paschal Full Moon was this morning and we had a brief total lunar eclipse to mark the exact time of Full Moon.
Usually, the Full Moon is not exactly directly behind the Earth, so lunar eclipses do not happen every month. This is because the Moon's orbit is tipped five degrees with respect to the Earth-Sun plane ("the ecliptic").
Last spring break we also had a total lunar eclipse and since our spring breaks always end on Easter, the question arises if lunar eclipses always fall on or near a Jewish or Christian religious holiday. Scanning NASA's Eclipse website at http://eclipse.gsfc.nasa.gov that Fred Espenak curates (Espenak is THE eclipse man), the short answer is "No." This morning's total lunar eclipse was the third in the current "tetrad" for four lunar eclipses coming every six months. The fourth will be September 28th. After that we'll have to wait until January 31, 2018 for another total lunar eclipse. The one following that is July 27, 2018. As far as I know, neither of those dates is a religious holiday.
Before 2018, there will be three penumbral lunar eclipses when the Full Moon misses the Earth's shadow umbra, so we'd be hard pressed to notice a change in the appearance of the Moon. The penumbral lunar eclipses are March 23, 2016, September 16, 2016 and February 11, 2017. Easter next year is March 27th which is close to the March 23rd penumbral lunar eclipse but the September 16th and February 11th eclipses aren't near a religious holiday. A partial lunar eclipse when part of the Full Moon touches the Earth's shadow umbra will happen on August 7, 2017. No religious holiday then either but school teachers will be in full swing of preparing for the coming school year.
On April 8th, Jupiter will stop its retrograde motion just shy of the Beehive Cluster in Cancer and begin moving its normal eastward drift among the stars towards Leo. Retrograde motion happens as the Earth catches up to and passes by an outer planet, so the outer planet appears to move backward relative to the celestial landmarks of the stars. For the rest of the spring and summer Jupiter will inch its way towards Leo. By the first week of August, Jupiter will have moved to being just above the bright star Regulus at end of the Sickle part of Leo (looks like a backward question mark on the sky). Jupiter is the super-bright "star" high up in the southeast after sunset and due south at 9 PM.
Earlier in the evening, Venus blazes away in the western sky after sunset. Venus climbs higher away from the Sun every week this month. Therefore, the time interval between sunset and Venus sets increases from three hours at the beginning of the month to about 3-1/2 hours by the end of the month. Tonight Venus is 8 degrees (slightly less than a fist at arm's length) below the Pleiades cluster at the shoulder of Taurus. On April 11th and 12th, Venus will be just a couple of knuckles at arm's length from the Pleiades. Venus will pass about half a fist width to the upper right of bright orange-red Aldebaran at the eye of Taurus on April 19th. The first star chart below is oriented to show both Jupiter, Venus, and the celestial landmarks I described at 9 PM.
Saturn is now undergoing retrograde motion among the stars of Scorpius. Saturn rises a little before midnight. It is now at the head of Scorpius. Its rings are tipped by almost their maximum extent, making Saturn even brighter than usual. Saturn's rings are made of trillions of small chunks of water ice, so they are especially reflective.
Around 3:30 AM, the constellation Sagittarius rises. The brightest stars of Sagittarius make a shape that looks like a teapot. Just below the lid of the teapot was the brightest nova since 2013 and the brightest nova in Sagittarius since 1898. Nova Sagittarii 2015 No. 2 was bright enough a couple of weeks ago that you could see it without any optical aid under dark skies (so definitely binoculars for the skies of Bakersfield). After that it faded to the very edge of naked eye visibility near the end of March it brightened again, so perhaps it is still visible to the naked eye under dark skies.
A nova happens in a binary star system where one of the stars has run through its life cycle and turned into a white dwarf. A white dwarf is the exposed super-compressed core of a former star with about as much mass as the Sun squeezed into a volume as small as the Earth. If the white dwarf in the binary system is close enough to its companion, it can suck up some gas from its companion. That gas piles up onto the white dwarf's surface getting hotter and denser as it does so. Eventually, the piled up gas gets hot and dense enough to undergo nuclear fusion. That burst of energy blows off some of the gas, relieving the pressure and the nuclear fusion shuts off. The gas builds up again and the cycle repeats with a period as short as a few years and as long as tens of thousands of years. The period of the cycle depends on the mass of the white dwarf with the more massive white dwarfs having shorter nova periods.
The second star chart below shows the 4 AM sky with Saturn's position and the position of Nova Sagittarii 2015 No. 2 marked. At the time of writing there was one ticket left for the Earthquake show on April 16th and many tickets left for the Dynamic Earth show on April 23rd. Get tickets from the BC Ticket Office or online from the link on the Planetarium's website.
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