By Nick Strobel
Tonight is the free monthly public star party with the Kern Astronomical Society that takes place from 8:30 PM to 10 PM or so, depending on foot traffic, at Russo's Books in The MarketPlace. The star parties this year are scheduled to fall on the Saturday closest to the First Quarter Moon when the Moon's position with respect to the Sun is such (about a 90 degree angle or half-way across the sky) that the craters really "pop out", especially near the day-night boundary. Tonight the Moon will be just one day before First Quarter phase, so it will be quite a sight through the KAS telescopes. Because we are so close to the summer solstice, the Sun sets late (around 8:15 tonight) so the sky will still be fairly bright with the twilight glow when the star party begins. However, the Moon will still be great at that time and Venus will be visible low in the west. Since Venus is climbing up from the Sun after being behind it, we see it in a gibbous phase, where more than half of it appears to be lit as seen from our (the Earth's) vantage point. Those with sharp eyes might be able to spot Mercury just a couple of knuckles at arm's length up and to the left from Venus when the star party begins while those with eyes like mine will be able to pick it out 15 minutes later (see the inset of the star chart below). A week later Mercury will have dropped below Venus and it will be much fainter.
Saturn will also be presenting its usual gorgeous self high up in the southern sky by then as well. Saturn will be the lower left corner of a triangle of bright points in the southern sky. To the right of Saturn about a fist width at arm's length away will be the bright star Spica at the lower right corner of the triangle and even brighter Arcturus will be nearly straight overhead (near the "zenith" point). For these past many weeks, Saturn has been slowly drifting westward (to the right or retrograde) among the stars as the Earth has passed it up in our faster orbit. Saturn will stop its retrograde motion at the end of June. As shown in the star chart below, the Waxing Gibbous Moon will pass close to Spica on June 18th. Those in parts of northern Africa will actually see the Moon hide ("occult") Spica in their evening sky (about 8 time zones ahead of us), clearly showing the proximity of our Moon.
Our season of summer officially begins on June 20-21st with the summer solstice. Why do I give a two-day range of dates? Well, the summer solstice is when the Sun reaches its northernmost position on our sky (its farthest position north of the celestial equator) in its annual motion among the stars and we have that position nailed down very precisely. The Sun will be at that point at 10:04 PM in our timezone on June 20th or 1:04 AM on June 21st in the eastern daylight timezone (EDT) and 5:04 AM on June 21st along the prime meridian ("universal time"). Therefore, your calendar might say that June 20th is the beginning of summer or it might say June 21st. Either date will work just fine---the night of June 20-21 will be the shortest night of the year for us in the northern hemisphere. Seasons are opposite in the southern hemisphere, so that northernmost Sun marks the beginning of their season of winter.
In solar system exploration news, last week we heard about the measurements by the long-running rover Opportunity of some rocks in an outcrop in Endeavour Crater. Opportunity landed on Mars over 9 years ago (it is now over 3200 martian days beyond its original mission) and it has been exploring rocks at various places to learn about the geologic history of Mars. Of special interest have been the rocks on the rims of impact craters and inside them because deeper layers from further back in time are exposed when an asteroid or comet hits the surface. Because deeper layers were formed further back in time than layers closer to the surface, the deeper the crater, the further back we can probe the geologic history. Endeavour Crater is the largest crater explored by Opportunity so far and it looks like Opportunity finally found some rocks from the earliest climate period of Mars. Mars has had three basic climate periods: the Noachian (the earliest, from 4.6 to 3.7 billion years ago), the Hesperian (3.7 to 2.9 billion years ago, and the Amazonian (2.9 billion years to the present). During the Hesperian climate period, Mars was drying out and the remaining water pools became quite acidic. Those are terrible conditions for life, though possibly some sort of acid-loving extremophile microbes might like it. Opportunity measured the composition of a rock outcrop called Esperance that appears to be from the Noachian climate period when clays were the primary rock type and the martian water had a neutral pH---just like the conditions when life began on the Earth. The biochemistry of life needs clays and water of neutral pH to get started.
Halfway around the planet, the more advanced Curiosity rover had already drilled several months ago into a rock from the Noachian period (so the rock had formed in water of neutral pH) and just a few weeks ago, Curiosity had drilled into another rock nearby and got the same results, confirming the first drill results. There was more than a sigh of relief when Curiosity first found those rocks that had formed in water of neutral pH because the many rocks sampled by Opportunity seemed to show that Mars' watery past was pretty acidic. Those rocks studied by Opportunity were from the Hesperian and Amazonian climate periods. With the results from the rock Esperance, we now see that Opportunity will be able to study the transition from the nice, habitable Noachian period to the harsher Hesperian period. While life probably needs water of neutral pH to get started, some forms of extremophile life might have been able to adapt to the changing climate as Mars dried up and cooled off and the water became much more acidic.
Opportunity is now heading to a location called Solander Point on the rim of Endeavour Crater that seems to be a geologist's dream. According to deputy principal investigator Ray Arvidson, it will be "like walking up to a road cut where you see a cross section of the rock layers." The location also has a very nice slope of the ground so that Opportunity can keep its solar panels tipped toward the Sun, enabling the rover to possibly keep active through the very cold martian winter. More astounding discoveries undoubtedly await us.
To close this column let me tell you about a couple of items on the exoplanet hunting front. In my previous column I wrote about the status of the Kepler spacecraft that finds exoplanets by looking for very tiny dips in a star's brightness as an exoplanet passes in front of the star. I described the list of over 2700 possible exoplanets or "exoplanet candidates" that still need to be verified. Another over 500 exoplanet candidates were added to the list late last week. What I didn't have space to describe last time was the first step in creating that exoplanet candidate list in which any interested person from the general public can help.
To create the exoplanet candidate list, many thousands of dips in star brightness, that may be from exoplanets passing in front of ("transiting") their stars, must be analyzed. These slight dimmings of the stars are called "raw data transit events". There are now over 13,000 raw data transit events to sift through. The Kepler team has developed computer algorithms to look for possible exoplanet candidates but computers can be made only so smart. The Kepler team released their over 13,000 raw data transit events to the public for others including the many people in the general public interested in the exoplanet search. You can look for planets too using the Kepler data with Zooniverse's Planet Hunters project at planethunters.org. The interface is simple and it doesn't take long to learn how to find those dips in the brightness. This project takes advantage of the excellent pattern-finding abilities of the human brain that is much better than any computer's. The first genuine exoplanet discovery from Planet Hunters was an exoplanet in a quadruple star system---yes, FOUR stars! The exoplanet named PH1 (short for "Planet Hunters 1") is slightly larger than Neptune and has less than half a Jupiter mass. It orbits the inner two stars (the primary pair) every 138.5 days at a distance that is inside the primary star pair's habitable zone. The other two stars are in a binary system that orbits the primary pair at about 25 times the distance that Pluto is from our Sun. There are probably more exoplanets in the system waiting to be discovered. Almost 19 million observations in the Planet Hunters project have been analyzed with 34 candidates identified. That 19 million observations includes many duplicate observations of any given transit event by multiple, independent people in order to verify a possible candidate. There are over 68,000 people in the general public working with Planet Hunters and they need more help, so give it a try!
Now that the Kepler mission has proved quite convincingly that exoplanets can be found using the transit technique, NASA recently approved the continued development of the Transiting Exoplanet Survey Satellite ("TESS" for short) with proposed launch in 2017. TESS has been in development since 2006 and its search field will be different than Kepler's. While Kepler went narrow and deep, TESS will go broad and shallow. TESS will look at a field of sky over 400 times wider than Kepler but focus on stars much closer to us than the ones Kepler has been studying. TESS will also be particularly sensitive to the stars that are smaller and cooler than the Sun. These are the types of stars that are most common in the Galaxy. Many of these nearby stars will be brighter than the ones Kepler looked at and any exoplanets found will therefore be easier to follow-up with the James Webb Space Telescope and ground-based telescopes.
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.