by Rex Parker, PhD
director@princetonastronomy.org

It’s Mid-Summer in AAAP.  Enjoying your “summer vacation” in Jersey or other exotic destination? It’s been a good stretch of weather for nature and green plants around here in central Jersey.  That’s a favorable trade-off from last fall when overly dry weather and drought was inescapable even though the skies were often clear. So, have you found an opportunity during the brief episodes of clear skies this summer to do any telescopic observing? Have you tried your hand at celestial-terrestrial photography with the Milky Way this summer? DSLRs, and cell phones such as the iPhone with night-mode setting, can capture the night sky with landscape surprisingly well, especially on vacation at a darker sky location. What have you discovered that is new to you, about the stars and the natural world and the cosmos?  What deeper questions arise in your mind as you go about your life with family, friends, work, and daily activities?  Sharing those thoughts, questions, and ideas about astronomy and physics is the raison d’etre for our club!  You can read about one of my projects with the color of stars below.

Here’s some good news for the club: the electrical cable problem has been repaired at Washington Crossing Observatory.  The permit was granted by the state and the professional electrician we hired completed the job in mid-July.  We now await only final inspection and “flipping the switch” by JCP&L.  I’d like to especially thank Michael Mitrano for relentlessly staying on top of the permitting and finding the electrician.  Also, a big thanks go to Dave Skitt for troubleshooting the problem and working to get it fixed, and providing an AC generator to power the observatory in the interim. 

ANNOUNCEMENT:  Launching the New AAAP Website (beta).  The AAAP is ready to launch a new, completely re-designed website.  While our current website has been effective and offers a classic feel, its origins go back to the mid-90’s with various updates along the way.  Changes in coding, formats, and approaches for modern websites prompted this upgrade, along with a desire for increased capabilities for club activities, security, and member usefulness. With this in mind, we are now launching the AAAP new website as beta version.  Members may access the new site at the URL address below.  Please note the site is not yet fully populated with content, hence the beta-designation. Some of the new members’ features and expanded capabilities of the website will require a log-in (for security), and guidance will be provided to members in the near future.  We’ll keep the original site going in parallel till around September.  In the meantime, we ask you to access the new site and begin to feel your way around.  In September we will review feedback and offer tips on using the new site. https://www.princetonastronomy.org/beta/

Major thanks go to the website development committee:  Jeff Pinyan, Mike DiMario, Gene Allen, Debbie Mayes, and Surabhi Agarwal.  In particular I and the Board thank Jeff for his skilled work and time and effort put into actually creating the website.  

How to Really See the Colors in the Stars. The sense of color in the stars by naked eye is subjective and often subtle.  But color is an important property that relates to fundamental physics of the stars.  In the scheme developed by astronomy, the letter sequence “OBAFGKM”, designates the stellar types from bluest/hottest to reddest/coolest.  Mostly due to the expense and complexity of spectroscopes applied to telescopes, it’s been difficult and a bit arcane to get into amateur astro-spectroscopy.  However, at nominal cost a low resolution yet modestly effective diffraction grating (the component that disperses light) with standard 1.25” filter threads is available.  This approach works with eyepieces, or better with astro-cameras in a variation on the standard telescope imaging setup.  Below are some initial results from my equipment in NJ in early July, using the “Star Analyzer 100” diffraction grating — a 100 lines/mm transmission grating.  I attached this in place of filter on my ZWO ASI-071MC camera and 12.5” reflector telescope, with adapter to give about 80mm spacing from grating to sensor (spacing is critical to disperse the spectrum to fit the width of the imaging sensor). 

In the panels below, the star is in the left center of the field (the zero-order spectrum) and the colorful first-order spectrum is dispersed to the right of each star.  The color patterns and the intensities across the wavelengths of light are related to the composition, temperature, size, and physics and chemistry of the stars.  Specialized software can make a graph of intensity vs wavelength (pixel position) from the original FITS image files. Though not shown here, this can reveal dark absorption minima in the spectra, the “fingerprints” of chemical composition. 

Shown below are spectra of two of the brightest stars of summer, Vega (blue-white type-A) and Antares (red giant type-M).  Differences can be readily seen in the extended red/orange and lesser blue of Antares compared with Vega.  The Ring Nebula M57 displays only blue-green and red components in the spectrum, consistent with O-III and H-alpha emissions that we see in astrophotographs (you may recall a similar spectrum of M57 first shown by Bob Vanderbei at AAAP at a meeting a few years ago). This was all from one night in July… many other stars are waiting in the wings to have their true colors revealed!