This month, in the early evenings, we have both the western and eastern horizon dotted with planets! And then, there are two more, if you face south higher in the sky that actually provide stunning views in a telescope!! In the east we have Mars and in the west we have Venus, which is extremely bright, and later in the month Mercury will make a brief appearance in the western sky, too. These worlds are very similar in size (Mars is slightly smaller than Venus, Mercury smaller still), and their composition similar. They are, all three (four if you include Earth), rocky worlds, meaning they have a rock surface structure. The appearance, though, when viewed in a telescope shows a huge difference. Mars can show surface detail, while Venus is shrouded in clouds.
These rocky worlds have other unique differences. Like Earth, Venus has a molten core but Mars doesn’t. Because of that Mars does not have the protective magnetic field. Venus is very close to Earth-size but something catastrophic happened to it that nearly stopped its rotation. Its day is longer than its year. Two of these planets, Venus and Mercury are orbiting closer to the Sun than Earth, and Mars orbiting outside Earth’s orbit make their apparent movement in our skies a little different. Venus and Mercury show us ‘phases’, round or crescent-shapes much like the Moon and easily seen in binoculars, and never do either of them stray far from the Sun. Mars, on the other hand, is the next planet out from Earth and so never shows us phases and from our vantage point can be seen sometimes all night long. Binoculars can show the color differences and phases. In July, Mars is closest to Earth, and viewing in a telescope will show the most detail possible at that time. There is a canyon, the length of which is as wide as the United States. Next month’s article will be about Mars.
The other two planets, more towards south and south-east are Jupiter and Saturn respectively. Both of these planets are simply AWESOME(!) to see in a telescope. They are Gas Giant planets, likely with a liquid Hydrogen core under extreme pressure, and what we view is only the cloud-tops. And, while both Jupiter and Saturn have rings, Saturn has the exquisite rings!! There is so much detail that can be seen, but we need the Earth’s atmosphere to cooperate. By cooperate, I mean be steady. If you see stars twinkling it is not steady. The atmosphere is rather turbulent, generally, but here in Arizona, the number one observing State with more professional telescopes than any other, the likelihood of clear, steady skies is very good. See for yourself, these five planets (six if you count Earth).
Steven Aggas is the Director at Apache-Sitgreaves Observatory, located in Overgaard, AZ, using the largest public viewing telescope in Arizona. Visit Apache-Sitgreaves.org for information on events and tickets.