Bakersfield College

Bakersfield Night Sky -- September 6, 2014

Bakersfield Night Sky – September 6, 2014
By Nick Strobel

Tonight the Kern Astronomical Society will have thei telescopes set out at Panorama Park for you to take a look through. They meet next to the walkway near to where Linden Avenue meets Panorama Drive (just west of Greenlawn Mortuary and Cemetery). Usually they meet the Saturday closest to the First Quarter Moon. However, for September that would have been the Saturday of Labor Day weekend when a lot of people, including the KAS members, are out of town or otherwise occupied with the "last weekend of summer." Tonight, we'll have a bit brighter Waxing Gibbous Moon just a couple days before Full Moon, but they'll still be able to show you Saturn and Mars, star clusters, and maybe even Comet Jacques (C/2014 E2) which is high up overhead near the center of Cygnus. You definitely need a telescope to see the comet. The first star chart below shows its location.

The comet passed closest the Sun in early July and then passed closest to us on August 28th. If the moonlight makes it too difficult to see the comet, then perhaps KAS member can move thelescope over to the open star cluster, M29, on the other side of the center of Cygnus. Cygnus is a swan flying down the Milky Way toward the southern horizon. Closer to the south horizon is the central bulge of the Milky Way, so there are a number emission nebulae and star clusters in that direction. That is also the direction to Sagittarius and the tail part of Scorpius. The stars of the brightest part of Sagittarius make a figure called the Teapot with the spout on the right or west side of the figure. Just a little right of the spout is the direction to the exact center of the Galaxy, hidden 27,000 light years away behind the thick, dark haze of interstellar dust.

At about the same height or altitude above the horizon to the right is a line formed by red Antares at the heart of Scorpius, white-blue Dschubba at the head of Scorpius, and the planets Mars and Saturn. Well, it's not a perfect line but it'll be easy enough to pick out at the star party tonight. Mars is now moving fairly quickly eastward toward Scorpius and in a week and a half, it'll be just above Dschubba. My planetarium program says Dschubba is a double star but Jim Kaler's Stars database says that it is very likely a quadruple star system with four stars in a complex gravitational dance and each star several times more massive than the Sun. The largest member of the system shines with about 14,000 times the energy of the Sun and is a variable star with a brightness that can change when it sloughs off a disk of gas at its equator due to its very rapid rotation. It last did that in 2000-2002. Dschubba is about 400 light years away.

Mars is getting fainter as we continue to move away from it in our faster orbit around the Sun. On September 21st it'll have a new visitor studying it when the MAVEN spacecraft arrives after a ten-month journey. The MAVEN mission will focus on Mars's upper atmosphere, ionosphere, and interactions with the Sun and solar wind. We're hoping that the data that MAVENgathers will enable us to finally figure out what happened to Mars's atmosphere. Long ago, Mars's atmosphere was much thicker and warmer than it is now. In our sky at the end of the month, Mars will pass above the "rival of Mars", Antares, so that placement will make it easy to compare their colors and see which is the redder one.

Saturn continues to poke along in the stars of Libra. Its rings have opened up a bit more, so should appear even nicer in the KAS telescopes tonight. However, Saturn is a bit lower in the southwestern sky than last month's public star party, so the Bakersfield haze might dampen the view somewhat. In the early morning sky, Venus and Jupiter continue moving apart from each other as Venus plunges toward the Sun and Jupiter rises away from the Sun over these next few weeks. The second chart below shows the pre-dawn sky tomorrow morning (September 7th).

Later this month will be the first show of the William M Thomas Planetarium's fall schedule. On September 18th will be "Oasis in Space" which is about our search for other places in the solar system that could have liquid water. On October 16th is "Ice Worlds" and on November 20th will be the ever-popular "Black Holes". The fall season will end with the holiday show "Season of Light" on December 4th and 11th. Bakersfield College is going to a new ticketing system through Vallitix. The move promises to make it easier to purchase and acquire the physical tickets as well as be more responsive to BC's needs in setting up the sales and receiving the income in a more timely manner. There is more of an overhead for the ticketing services. Tickets will be $8/adult and $6/senior and children 5 to 12.

In the last part of this column I'll describe how tiny the planets are compared to their distances from each other and the Sun. This is a topic that comes up in the first week of school in a couple of ways. One way is through a scale model I have my students walk with me on the BC campus. If we walk from the Planetarium northward to Panorama Drive, I can get the planets out to Uranus to fit. Neptune and dwarf planet Pluto are beyond the bluff. This semester with all of the construction going on to replace the decades-old water and gas lines, I had them walk eastward toward Mt Vernon. We could only get Saturn to fit on the campus and Uranus would have been in the middle of Kern Schools Credit Union. On this scale, the Sun is about 6.5 inches across, the Earth is a large grain of sand about 18 meters from the Sun, and Jupiter is the size of a dime about 92 meters from the Sun. The closest star beyond the solar system would be beyond the bounds of the United States---all the way to Nova Scotia. That scale model is given in my free online textbook at www.astronomynotes.com/chapter1/s2.htm .

The second way is a bit more subtle in that I have the students compare the Sun's spectrum a space telescope would record at the Earth's distance from the Sun vs. a space telescope at Pluto's distance from the Sun. A spectrum is what you get when you take the light from an object and spread it out into its rainbow of colors. Well, since both space telescopes are looking at the Sun, they would see the same pattern of colors and dark lines that tell us what the Sun is made of and how hot it is. Since the Sun's composition and temperature don't depend on how distant it is from our telescope, the space telescopes should see the same spectrum. Yes, the spectrum of the Sun seen from Pluto's distance will be fainter than what we see from Earth's distance but the pattern of colors and dark lines will be the same. We would simply have to have a longer exposure for the Pluto telescope's solar spectrum to have the same brightness as the space telescope at Earth.

Okay, so what does that have to do with planet distances and sizes? Well, one answer I see every semester is that the space telescope at Pluto should be different than the space telescope at Earth because the rest of the planets will be getting in the way---they will be blocking the view. This makes sense if you recall the typical picture of the solar system given in books or on websites: Sun at one side and the planets all lined up and big enough to easily see and all fitting nicely within that six to eight inches of the picture. The solar system picture will usually show Jupiter and Saturn being much larger than the Earth, so the artist is trying to give some semblance of scale to the sizes of the planets. The distance scale is very, very wrong, of course, as you would need more than a mile of space to match the size scales of the planets in that picture.

Consider the scale model I have my students pace out: if the Sun is a ball 6.5 inches across, it will indeed look small as seen from 700 meters away for Pluto's average distance but the planets would be microscopic. Even if they were all lined up (which never happens), those tiny planets (even Jupiter which is the size of dime) wouldn't be visible as disks from Pluto's distance. They would be mere points. It got me to wondering though, how much of the Sun would the planets block as seen from Pluto, so I set out the calculate it on the Saturday afternoon of Labor Day weekend. Now remember that I'm an astronomy teacher, so exercises like this I actually consider "fun".

What would be absolute maximum that the planets could cover up the Sun as seen from Pluto if they were all approximately in the same plane and lined up such that one planet does not block another but still would be in front of the Sun? Let's ignore the fact that Pluto's orbit is significantly out of alignment with the planets and the planets don't ever line up to pass in front of the Sun at the same time. Let's assume that we're observing from Pluto's closest distance to the Sun and the planets are at their farthest distance from the Sun in their slightly elliptical orbits around the Sun. This, of course, never happens either because the planet orbit ellipses are not no neatly arranged as that. However, with this setup the planets would be closest to Pluto, so they would appear the largest they ever could.

We do have to ignore Neptune in this experiment since Pluto's orbit does cross inside of Neptune's orbit. If we don't ignore Neptune, then Neptune would be right on top of Pluto, swallowing it up whole. However, Neptune and Pluto are always positioned so that Neptune is very far from Pluto when Pluto is crossing inside Neptune's orbit. Furthermore, Neptune is never going to come in between Pluto and the Sun. For the rest of the planets in this artificial scenario, all of them are covering up a tiny part of the Sun but not blocking another planet, so the observer at Pluto sees seven dots in front of the Sun. It turns out that the seven planets (Mercury to Uranus) would block just 4.4 percent of the area of the Sun's disk. Pretty small but detectable!

Looking at the planets from the other stars, the planets would block a much smaller fraction of the Sun's surface. From 10 light years away (still very much in the Sun's "back yard" compared to the rest of the Milky Way), all of the planets including Neptune added together would block less than 2% of the Sun's surface. The situation is reversed when we're looking for exoplanets crossing in front of their star as seen from near Earth and real exoplanets are not going to be all nicely lined up to transit their star at the same time. More about transiting exoplanets in a future column.

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.

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

Early September 2014 at 9 PM looking South

Early September 2014 at 6 AM looking East

Kern Community College District