This is Dudley Observatory’s Skywatch Line for Friday, November 20, through Sunday, November 22, written by Sam Salem.
On Friday, Sun rises at 6:54am and sets at 4:28pm; Moon rises at 12:21pm and sets at 9:56pm. Moon sits in the middle of constellation Capricornus the Sea Goat, east of constellation Sagittarius and planets Jupiter and Saturn, on Friday.
The Moon completes the first quarter of its orbit around Earth at 11:45pm on Saturday. At that time, the relative positions of the Earth, Sun, and Moon will cause us to see Moon half-illuminated, on its eastern side. At first quarter, the Moon rises around noon and sets around midnight. The evenings surrounding first quarter are the best for seeing the lunar terrain when it is dramatically lit by low-angled sunlight. The small, round Mare Crisium, as well as Mare Fecunditatis and Mare Nectaris are easily visible on the Moon’s face. Through a telescope, look for the crater Theophilus, which has a prominent central mountain comprising three peaks that rise just over a mile above the crater floor. On Friday night, the crater should appear in sharp relief just to the right of the terminator, the line that divides lunar night from. Use a lunar map to help you identify the Moon features.
As dawn brightens Mercury is still nicely visible. If you have a low view to the east-southeast, look for Mercury lower left of Venus. Next week it will descend from sight down to the dawn horizon. The 3rd-magnitude star sitting about 1 degree to Mercury’s right is Alpha Librae. Look for Beta Librae farther off to the left.
On Sunday night, use the Moon to find the star Fomalhaut in the constellation Piscis Austrinus the Southern Fish. In that direction, you will be looking away from the flat plane of our Milky Way, where most of our galaxy’s stars reside, and toward intergalactic space. When you look at the Loneliest Star Fomalhaut you are looking some 90 degrees from the plane of our galaxy’s equator. When you look toward Fomalhaut, you’re looking away from the Milky Way pancake, and out the south window of the galaxy. When the Moon is no longer there to guide you, try star-hopping from the Great Square of Pegasus to Fomalhaut. The 4 stars making up the Great Square of Pegasus might be visible, despite the moonlight. The Great Square of Pegasus appears high in the south to overhead by around 7pm in late November. Draw a line through the Great Square’s two westernmost, or right-hand, stars. Extend that line southward to land on the bright star Fomalhaut. Once you find Fomalhaut, you’re looking out the galaxy’s south window. The exact location of the south galactic pole lies east of Fomalhaut, in the faint constellation Sculptor.
Friday marks the 131st. birthday of Edwin Powell Hubble. Hubble’s name is most widely recognized for the “Hubble Space Telescope”, which was named in his honor. The American astronomer is considered the founder of extragalactic astronomy who provided the first evidence of the expansion of the universe. Hubble proved that many objects previously thought to be clouds of dust and gas and classified as “nebulae” were actually galaxies beyond the Milky Way. In 1923 to 1925, he identified Cepheid variables in “spiral nebulae” M31 and M33 and proved conclusively that they are outside the Galaxy. Hubble provided evidence that the recessional velocity of a galaxy increases with its distance from the Earth, a property now known as the “Hubble–Lemaître law” which implies that the universe is expanding. Earlier in 1912, the American astronomer Vesto Slipher was the first to observe the shift of spectral lines of galaxies, providing the first evidence that the light from many of these nebulae was strongly red-shifted, indicative of high recession velocities.