Look Up Before Sunrise for the Next Month to See 5 Planets at Once
From tomorrow morning (January 20) through February 20, you can look up at the predawn sky and spot Mercury, Venus, Saturn, Mars, and Jupiter in a more-or-less straight line. It's the first time in over a decade that the predawn sky has hosted all the five easily visible planets of the solar system at once. Like celestial Pokémon, this is your big chance to catch them all.
Sky & Telescope has a viewing guide for how to spot the planetary bonanza. In the northern hemisphere, the brightest planet will be Venus in the southeast. Saturn will be higher and rightward; continue in that direction to pick up each planet through Jupiter. To find Mercury, scan back to Venus and continue down and to the left. It will be just above the horizon and will likely be the most difficult of the group to spot. The situation will improve by the last week of January, when Mercury will appear higher in the sky, but the planet will once again become harder to see after the first week of February, Sky & Telescope notes.
IS THAT A PLANET?
If you're going to get out of bed that early—about 45 minutes before dawn—you probably want to be sure the dots you're seeing are planets and not stars. One way to tell is by their twinkle. Generally speaking, stars appear to blink and planets do not.
Here on Earth, when the light of a star (other than the Sun) finally arrives, it appears as a single point. As that point of light encounters the turbulence of our atmosphere, it is refracted, its image effectively bounced violently about. As a result, sometimes the point appears as two points; sometimes it appears as no point at all. To be clear: The star and its light are just fine, as unblinking as the Sun. It's just that the light isn't always making it to your eyes—thus the twinkle.
Planets, on the other hand, are close and bright, and their light reaches us as discs rather than points. So even though refraction is occurring, something is always getting through, and the light therefore appears steady. The exception to this is when planets are very close to the horizon. This sometimes makes them appear to twinkle, as you're staring through a lot more of the Earth's atmosphere.
If you were in space looking down on the solar system, you would not see a straight line of planets for the next month. In fact, you would see this: the first six planets of the solar system in relatively close proximity on the same side of the Sun. (Saturn is pretty far out there—just under 1 billion miles away—but its size and brightness compensate.)
Terrestrially, if you want to see the five planets simultaneously, you will want to find an area with a good view of the horizon. As always, avoid areas with strong light pollution. If you're unable to get a clear view of the sky for the next month (or if you can't stop hitting the snooze button), the next chance to see five planets at once will be on August 13, when they will then appear in the evening sky. However, because Mercury and Venus will be much lower to the horizon, spotting all five will be a much more difficult endeavor.
A general note about planet- and stargazing: If the streetlights in your neighborhood remain lit all night long, contact your local government and inquire about what might be done. (Even the Eiffel Tower goes dark every night.) Motion sensors are an option. Other solutions include the installation of fixtures that aim light downward—at the street, where light is needed, as opposed to outward or upward, where it is not.