While the five naked eye planets (Mercury, Venus, Mars, Jupiter and Saturn) are only visible in the late evening and early morning hours, Uranus and Neptune are well situated for early evening viewing this month. If you want to add to your bucket list the feat of seeing all seven planets (other than the Earth), this could be your chance. Uranus is a sixth magnitude planet which cannot be seen without either a pair of good binoculars, a telescope or a DSLR camera with a time exposure.
Knowing where to look is the biggest challenge and the moon can help you this month by acting as a guide. On the 23rd of January, sixth magnitude Uranus will be 5 degrees above and to the right of the quarter moon. It looks like one of many similar stars in the neighborhood, but it is the only one that is blue. If you have a telescope with a “go-to” feature, you can point it directly at Uranus but otherwise it might be helpful to try to see a square made by the stars Omicron Pisces at magnitude 4.25, Nu Pisces at 4.45, Mu Pisces at 4.80 and Uranus. Using planetarium software such as Stellarium in advance will help you visualize this pattern.
In the case of Neptune, seeing it is more of a challenge since the planet is only eighth magnitude in brightness. On January 20th, Neptune is just two degrees to the right of the crescent moon and just to the left of Lambda Aquarius, a 3.7 magnitude star. Again, Neptune will not be different from other stars except for the fact that it is blue in color. Looking to the west shortly after sunset is the best time to do your observation.
If you don’t have a telescope but have a DSLR camera and a tripod, you could try photographing these planets instead. Set your camera in manual mode with an ISO of 1600, f-stop of 5.6, zoom set at maximum telephoto, and an exposure time of 15 seconds. Try not to get the moon’s image in your photo because it will tend to wash out the picture, since it will be severely overexposed. After taking a few different shots, return home and compare your best photos with the Stellarium view of the same sky at the same time. With luck, you will see the blue dot of either planet in the location where the software predicts it should be.
The discovery of these two planets are interesting stories. Since the five naked eye planets have been known since antiquity, the discovery of Uranus in March, 1781 was really big news. It was discovered by accident by an amateur astronomer named William Hershel (There is hope for us in the AAA). He was trained as a musician but became an avid hobbyist and built his own six-inch Newtonian reflector telescope when none that size was available. After his discovery, he was knighted by the king of England and received an annual stipend so that he could devote all his time to astronomy. He became a master at building larger and larger telescopes, grinding the mirrors by hand, making a 20 foot telescope with an 18.5-inch mirror and finally an unwieldy 40 foot long reflector with a 48-inch diameter primary mirror which proved impractical.
The discovery of Neptune is a much different story. After the discovery of Uranus there was great interest in looking for an eighth planet. This time, mathematicians and astronomers worked together. They noticed that the orbit of Uranus was perturbed or offset by some unknown mass. A French mathematician named Urbain Le Verrier calculated the position of this mystery object and German astronomer Johann Gottfried Galle found it where it was predicted on September 23, 1846.