In this week’s discussion topic, I attempt to answer the question “Why are Uranus and Neptune distinctly bluer than Jupiter and Saturn?”
On Uranus and Neptune, the methane absorbs red, orange and yellow light, reflecting back the blue. In contrast, Jupiter and Saturn have only minor trace amounts of methane and quite a bit more hydrogen and ammonia.
My second post in my series of weekly discussion topics for my Introduction to Astronomy online class. Last week I got up close and personal with the many sides of the Moon. This week I take a closer look at the other blue planet in our solar system and how we discovered it without observing it first.
Why was the discovery of Neptune a major confirmation of Newton’s universal law of gravitation?
Before Newton, astronomy relied on observational data from which mathematical formulae and equations were created. Newton pioneered an approach which allowed mathematicians to extrapolate and predict the movement of objects using three assumptions, now commonly known as his laws of motion. Together with his formula for gravitational force, Newton transformed Kepler’s three laws to predict orbits of comets and other solar system objects. He further formulated a mathematical model, known as the Law of Universal Gravitation, that describes the behavior of the gravitational force that keeps the planets in their orbits. (Comins, 2015, p. 42-44)
Autumn arrived mid-week here in the Heart of America, but you wouldn’t have known it by looking at the weather forecast: Mid 90s and moderately high humidity. Also with the change of the seasons, I retired my FitBit Charge (or rather it retired itself by falling apart) and upgraded to a Samsung Gear Fit2. The new fitness tracker is spurring me on to be more active, although my sleep pattern hasn’t improved much. I can safely blame work (10 pm to 4 am conference call on a Saturday night/Sunday morning) and astronomy, which requires, well, dark skies, for my reduced snooze time.
Star gazing and planet seeking were not on my Friday night list of must do things. All I really wanted to do was relax after a long stressful work week. And for the most part I accomplished that goal. But I couldn’t resist the siren’s call of the seventh planet. I peeked out the back patio door after nine o’clock and noted the bright nearly quarter moon shining in the southwest. The skies were somewhat clear, not perfect, but better than last weekend by a long shot.
I went back inside and grabbed a folding table, my star charts, the binoculars and a portable battery that includes a bright red light I could set on the table to illuminate my maps. Oh, and my reading glasses so I could actually see said maps.
I took out my observing checklist that I prepared over a week ago for the dark of the moon weekend (the one where the skies remained hidden behind clouds). I had several stars I needed to locate. Using my Pocket Star Atlas and my binoculars, I got in the neighborhood, but the objects were too faint and my night sky not dark enough to find them. I decided to switch from stars to seeking the planet Uranus.
I looked east over the roof of my house. I could see the Great Square of Pegasus, but not a single star visible in the constellation Pisces. I needed to find those stars, or I would not be able to find Uranus. I also needed the stars to move westward a bit more to clear the roof and to get into the thinner atmosphere directly overhead.
I returned to the interior of the house, where Terry and I squeezed seven lemons and added some freshly made raspberry syrup to the blender to make some iced raspberry lemonade. Our initial taste testings resulted in a quite tart concoction, which we shelved it in the refrigerator to tackle again on Saturday.
I went back outside after ten o’clock and closely reviewed the special chart provided by Sky & Telescope via an article on one of their observing blogs entitled ‘Uranus and Neptune in 2012.’ I made sure to print that PDF (something I rarely do these days) and kept it close by both my binoculars and the telescope. Despite the fact that I could not see a single star in the constellation Pisces with my naked eyes, I forged ahead with my binoculars, star hopping my way to 44 Pisces and Uranus. For a good online article on how to use a star map at the telescope, check out this Sky & Telescope link.
Here’s a breakdown of the star hop that worked for me:
I followed these landmarks repeatedly with my binoculars. I got very good at this particular highway in the sky. Translating these landmarks, first to the finder scope and ultimately to the telescope’s eyepiece proved much harder. First, the field of view in the finder scope (9×50; 5 degree f.o.v.) appeared wider than my binoculars, which are 7×35.
According to the XT8’s Instruction Manual, both the finder scope and the view through the eyepiece of the telescope produce an image that is upside down. I guess I should be grateful that the eyepiece field of view is not also reversed, like it is in my ETX-90. My brain doesn’t have any trouble flipping what my retina receives around. I learned that trick years ago as a legal secretary, when I had to stand before my attorney’s desk and keep up with what he was discussing from the sheet of paper he was reading from in front of him. I can also flip things in a mirror with little difficulty. But doing both takes a bit more brain processing power.
When I looked through the finder scope at Alpha Pegasi, I had to keep reminding myself to go in the opposite direction I had with the binoculars. Even though the field of view in the finder scope seemed larger, my brain thought it was smaller (probably because I was only using half my eyesight). I finally got to my destination, 44 Piscium and, drum roll please, Uranus.
After visiting the seventh planet for a few minutes, I moved on to fishing for the eighth and final planet. With Pluto’s demotion to a dwarf planet, and being a native Kansan, I plan to follow in the footsteps of Clyde Tombaugh and eventually discover Pluto for myself. But for the moment, I needed to fish for Neptune in the constellation Aquarius.
I found the stars near Neptune easily with my binoculars. And the short hops with the finder scope proved easier than finding 44 Pisces and Uranus. But try as I might, I could not discern which faint star might have a twinkleless blue tinge. I couldn’t confirm I found the eighth planet, so I won’t check it off my list. I did feel satisfied that I could at least get to the neighborhood repeatedly, without referring to the star charts as often.
Midnight crept up on me and I marveled at how the time slips away from me when I’m stargazing. I hoped all my practicing would come in handy Saturday night, when I planned to pack everything in the van and make the trip south to Powell Observatory for some serious observing.
I couldn’t wait for midnight Friday night. The forecast for the weekend seemed unbelievable, especially after the scorching heat of the last month. Clear skies and mid to lower 80s for the high temperatures over the next several days. I came home from work to a grilled steak and baked potato dinner, prepared by Terry. Mmm-mmm good.
After dinner, Terry and I began reviewing the DVR play list and guide, deciding to delete many old recordings to free up some disc space. Our daughter called and chatted with us for about forty-five minutes. The conversation ended abruptly when her phone battery died.
For dessert, Terry blended a frozen raspberry lemonade. I read for a few minutes, while slowly sipping the drink (trying to avoid a brain freeze). I asked him to wake me up around midnight so I could scout the skies in search of the Andromeda galaxy and the planet Neptune. Apollo followed me upstairs to the bedroom to join me in my nap.
Terry woke me up just shortly after midnight. I rubbed the sleep out of my eyes and found my flip flops. I followed Terry back downstairs to the band room and walked out the patio door to the back yard. The skies were clear, if not what you’d call dark (why do my neighbors leave their porch lights on all night long?). I went back inside for one of my star charts and a pair of binoculars. I didn’t trust myself to lug the telescope outside in the dark, not being completely awake yet. A survey with the binoculars should be sufficient for my first attempt.
I walked out into my backyard, towards my one remaining pine tree and turned back around to face the east. What a difference a couple of hours makes! I could clearly see the Great Square of Pegasus hovering directly over my roof. In fact, my chimney seemed to be pointing a finger at the famous flying horse. I remembered what I’d read in the EarthSky post about finding the Andromeda galaxy and put what I’d learned to good use. With just a pair of mediocre binoculars, I easily found the smudge that is M31. Now I regretted not moving the XT8 outside before I took my nap.
I turned ninety degrees to the right and began scanning the southern skies. I can’t see most of the southern horizon, which is blocked by my neighbors tall trees and houses (and all the exterior lighting attached to them). I lose a good twenty if not thirty degrees of sky in all but one direction, to the southwest I can see a bit of horizon, but only through the even worse light pollution generated by the parking lot of a doctor’s office and the streetlights along Main Street (also known as K-7/US-73).
I needed to find the constellations Aquarius and Capricornus. The ecliptic passes through both of these constellations. Neptune swam the night skies somewhere between the two constellations on the invisible ecliptic course all the planets chart. The trouble in finding Neptune in this area of the sky comes from a lack of bright stars to anchor from for star hopping. I spent the next hour comparing the star atlas from my pocket guide to the stars I saw through the binoculars and eventually convinced myself I had found the southeastern tip of Capricornus. Just above those stars, I believe I found the two brightest stars in Aquarius, Sadalmelik and Sadalsuud, but those two stars were too high above the ecliptic and too far away in the field of view of the binoculars to find Neptune. I needed to do more research and next time use a telescope to help cut through the fog of light pollution.
After an hour, I returned inside and went back to bed, resolved to research better star charts in the morning.
I went back to Astronomy.com and re-read the article on Neptune, but I just couldn’t relate their star chart (shown above) to what I’d observed last night through the binoculars. I would need more magnification and a more steady mount to zoom in and match up the stars shown above to the field of view of the XT8.
I tried Sky and Telescope’s web page and found a better set of charts in a PDF format in their article about Uranus and Neptune visibility during 2012. I downloaded the document and will print it today to keep with the rest of my star charts.
Saturdays are always packed full of activities, so I’m hoping I’ll still have the energy tonight to make a second attempt at finding Neptune. My scouting trip showed me what I needed to overcome before I proceed with netting Neptune.