Bakersfield Night Sky - March 2, 2013

By Nick Strobel

Just a few more weeks to Spring Break at schools across the city, including Bakersfield College.

Spring Break is early this year because Easter is early this year. The timing of Easter is tied to the first Full Moon after the northern hemisphere spring equinox.

Easter happens on the Sunday following the first Full Moon after the spring equinox. The spring equinox for the northern hemisphere is when the Sun crosses the celestial equator (projection of the Earth's equator onto the sky) heading northward.

Since the Earth is tipped by 23.5 degrees with respect to its orbit path around the Sun, the Sun's apparent motion among the stars (the “ecliptic”) is a great circle tipped by 23.5 degrees with respect to the celestial equator and the two great circles intercept at the points called “equinoxes” since every place on the Earth will have twelve hours of daylight and twelve hours of night (equal night = “equi-nox”).

I know my meteorologist friends will say that it is not really twelve hours of daylight because they measure sunrise when the top of the Sun's disk peeks above the horizon and sunset is when all of the Sun's disk is below the horizon. Therefore, the true twelve hours of daylight happen a bit earlier than the equinox. Fine!

The equinox happens when the Sun reaches a particular point with respect to the celestial equator and we have that nailed down very precisely: 4:02 AM Pacific Daylight Savings Time on March 20th. (Daylight Savings Time begins Sunday, March 10th.)

Full Moon occurs on March 27th (at 2:27 AM PDT to be more precise), which is a Wednesday. Therefore, Easter is on March 31st this year. March 31st is also when the Moon will be closest to the Earth (“at perigee”) in its elliptical orbit. The previous perigee will be on this Tuesday, March 5th.

I go back and forth each year on whether I like having Spring Break tied to Holy Week (Palm Sunday to Easter).

As an educator, I prefer having the spring break to be at least fixed on a certain week in the semester - or even better, to not have spring break - because it breaks the flow of learning in the middle of the term and it always takes the students a few days to get back in the swing of things after being gone so long.

On the other hand I do enjoy the chance to catch up on some sleep after 60-hour work weeks and being able to participate in the celebrations of Holy Week at Wesley UMC.

Right before Spring Break will be a showing of “Dynamic Earth” at the William M Thomas Planetarium on March 21st.

Dynamic Earth is about some of the various processes and features of the Earth and surroundings that make Earth be such a nice place for complex, multi-cellular life to exist on the surface.

These processes include the magnetic fields of the Earth and Sun, circulation of gases in the atmosphere and water in the oceans, plate tectonics, and the carbon dioxide cycle. There are other processes on the Earth intertwined with each other that are necessary for a planet to have complex life because complex life is very fragile and picky about its environment in comparison to microbial life.

Microbes are tough; we are not.

Last month was the month of the asteroids. This month was to be the month of the comet.

Comet PanSTARRS (C/2011 L4) was supposed to put on a nice show for us in the evening sky just after sunset beginning next week and continuing through to the end of the month.

However, the latest reports I have as I write this say that Comet PanSTARRS's peak brightness will be like that of just a medium-bright star in our sky without a telescope. Still pretty good for a comet, but you'll need binoculars to have a really good view.

Comet PanSTARRS is expected to be at its best for us between March 8th and 20th, especially March 12th to 17th. A super-thin Waxing Crescent Moon will be right next to the comet on our sky on March 12th.

A comet's brightness is very difficult to predict because it depends on how the dust, rock and volatiles are mixed together in the dirty iceberg we call a comet nucleus and how easily the volatiles vaporize as they approach the Sun. Each nucleus is different.

Comet-hunter David Levy said it well, “Comets are like cats; they have tails, and they do precisely what they want.”

So perhaps Comet PanSTARRS will have a nice outburst and put on a spectacular show. All we can do is go out and take a look.

Comet PanSTARRS will be closest to the Sun on March 10th, getting to just within the orbit of Mercury. The comet will be nearest the Earth on March 5th at a very safe distance of 1.10 AU (102 million miles) from us.

See the Comet PanSTARRS Orbit page for views of the the comet's orbit from various vantage points.

On that page you will see how the comet's orbit is oriented with the Earth's position at the time it passes near the Sun and why we in the northern hemisphere have to wait until near its perihelion passage for us to have a good view of the comet.

The first chart below shows the position of Comet PanSTARRS with respect to the western horizon at 6:25 PM.

The “with respect to the western horizon” part is important, because usually I show the positions of objects with respect to the stars.

Over the two-week span of the attached chart, the stars will have significantly shifted position with respect to the horizon at a given set time. Constellations due south at a given time at the start of the month will have reached the due south position almost an hour earlier in the night two weeks later.

Although the chart shows Mars, it will be too close to the Sun on our sky for us to see. Mercury has also now left the scene as well.

Jupiter will be the very bright star up in the southwest sky next to Taurus' head in the evening. Jupiter will set at around midnight and Saturn will become visible rising in the East around 11 PM, so there will an hour span of time when you will be able to see the two largest planets in our solar system up at the same time but on opposite sides of the sky.

The Waning Gibbous Moon will rise around midnight. The second chart below shows the early morning sky when Saturn's position is due South at 4 AM.

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. Visit the Dark Sky International website for more info.

• Nick Strobel
• Director of the William M Thomas Planetarium at Bakersfield College
• Author of the award-winning website www.astronomynotes.com