Mars lies high in the western sky after sunset, joining the stars of Taurus the Bull. It shines at magnitude 1.3 on April 1 and fades to 1.6 by the end of the month. Compare the Red Planet’s signature orange-colored glow to Aldebaran, the Bull’s magnitude 0.9 star. Aldebaran, a glowing star emitting its own light, appears reddish due to its “cool” surface temperature around 6,700 degrees Fahrenheit. But Mars is a cold, rocky planet and has no light of its own. Instead, its ruddy color occurs because it reflects sunlight preferentially in the red part of the spectrum, due to the makeup of its rusty surface material.
Mars tracks slowly through Taurus. Between April 12 and 13, it passes between the two stars marking the horns of the Bull — Alheka (Zeta [ζ] Tauri) and Elnath (Beta [β] Tauri). The planet crosses into Gemini April 24, then early on the 27th passes delightfully 0.5° north of M35, a fine open cluster in Gemini with a few colored stars. Grab a pair of binoculars to soak in this stunning sight, as well as pick up an additional target: Located just 0.5° southwest of M35 is an even more distant cluster, NGC 2158.
On April 30, Mars forms a nice triangle with the well-known 3rd-magnitude pair Eta (η) and Mu (μ) Geminorum. By now, Mars sets shortly after local midnight, so it’s best to catch the planet soon after twilight for the best views. The disk spans only 5.3" on April 1 and slowly shrinks to 5" by the end of the month, so telescopic views are challenging at best.
Once Mars sets, it’s more than four hours before another major planet rises. You can use the middle of the night to search for the brightest of all asteroids, 4 Vesta, which reached opposition in Leo the Lion last month. Vesta is an easy binocular object at 6th magnitude, now moving across the central region of Leo. Comparing its position on consecutive nights will reveal its motion relative to the background stars. On April 1, it’s 2° due east of 51 Leonis. This star is most easily found by scanning midway between Algieba (Gamma [γ] Leonis) and Chertan (Theta [θ] Leonis). By mid-April, Vesta lies only 0.6° southeast of 51 Leonis; it then swings southward, ending the month just over 1° southeast of the star.