Jupiter/Saturn Conjunction

December 21, 2020

See the two largest planets right next to each other as seen in our sky!

This conjunction will be a very nice holiday treat! Our two largest planets, Jupiter and Saturn, will be seen so close together in the sky that it will be a challenge to see them as separate objects with the unaided eye. Please look at the three images to the right.

Looking at the widest view, we see the horizon stretch across from south to west, centered on the south-west. You’ll see the first-quarter Moon toward the south. Also to the south, but much higher, you’ll see the red planet Mars. At twilight, around 5:30 p.m., you’ll see a very bright object about 20° above the south-west horizon. It will look like one object, but will be Jupiter and Saturn! This is the time to start looking. As darkness approaches, we witness the rotation of the Earth. We are rotating so that we are more fully immersed in the shadow of the Earth. Another effect is that the Earth is rotating away from our view of these two planets. Thus, they are seen to look like they are sinking lower in the sky. Waiting until later may mean these planets may be blocked by nearby trees, houses or mountains. Darkness comes at about 6:30 p.m. At 7:36 p.m., the Earth has rotated enough for the planets to be seen going below the true horizon. So, you have a small time window to see this conjunction.

The weather is another factor to consider. If you know the weather will be poor on the 21st, look the days before or after. The two planets won’t be as close, but will still be impressive.

If you have binoculars, the second image shows what you’ll see. The outer red circle represents a 4° field of view. This is similar to the view of most binoculars. You should be able to resolve the two planets now. They are at 6’18” separation. This means that they are 6 arcminutes, 18 arcseconds apart. You may ask yourself, what does that mean? If you trace out a circle all around you, like a hula hoop, that is 360 degrees (360°). That 4° binocular view is 4/360th = 1/90th of a full circle. A very small amount. Your index fingertip at arm’s length is about 1° wide. If the minutes and seconds part reminds you of a clock, it should. How many minutes are in an hour? 60. In mathematics, there are 60 arcminutes in one degree. And, there are 60 arcseconds in one arcminute. Our planets then, are seen about 1/10th the width of your fingertip apart!

The third image shows two telescope views of Jupiter and Saturn. The left image represents a common view of most smaller telescopes. At 91x, the two planets are easily viewed as well as their largest moons. The very unusual part is that they are seen in the same view! The right image is at 369x, an image from larger or better scopes. Both planets are still in the same view! This image, though, labels the bright moons orbiting each planet. Be aware that both of these views are with a refractor, a telescope with a lens in the front that gathers the light. The image is mirrored left-right. A reflector telescope that has a mirror in the back that gathers the light will provide a correct image, but upside-down.

Jupiter and Saturn are both gas giant planets. They are part of the Jovian planets that also include ice giants Uranus and Neptune. Jupiter and Saturn are so large, that they have an enormous atmosphere, made of gasses like hydrogen, ammonia, methane and much more. 1,000 Earths could fit inside Jupiter. 850 Earths for Saturn. Saturn, though, has those fabulous rings. The rings are made of small rocks and mostly ice. The rings are also larger than Jupiter. Binoculars will not clearly resolve the planets to the point of seeing the rings of Saturn. Saturn will be seen as not quite round, though. A telescope will easily show the rings of Saturn and should show the dark and light banding of clouds on the outer cloud surface of Jupiter.

Hopefully the weather will cooperate and you’ll see this very nice conjunction in your own back yard!

Mars at Perihelic Opposition

September & October 2020

Mars will look larger than normal. Your telescope may show surface features!

There’s about two months in which Mars will look larger than normal in a telescope centered on October 6, 2020. Why? Mars is the fourth planet from the Sun. Earth is the third. There are times, about every two years, in which the two planets are on the same side of the Sun. This is called opposition. Mars is opposite the Sun in the sky. No, Mars will never look unusually large and NEVER as large as our Moon. You’ll still need a telescope to see Mars as a tiny disk and with a good amount of magnification. If you have a telescope, this is a good time to try to eke out some dark and light markings on the surface of Mars. The first thing you’ll see is the pale, orangish color of the planet. That is the sand covering this desert world. There is iron oxide (rust) there, providing the color. Then you might see the southern ice cap comprised of frozen water. The southern hemisphere is facing the Sun, so it has warmed up enough to evaporate the frozen carbon dioxide at the pole (CO2) also known as dry ice. Remember, its freezing point is at a much colder temperature than water’s. Then, if you are really lucky with good optics and steady viewing, you’ll see dark markings on the surface. That will be exposed lava rock called basalt. Guess what, the Moon and Earth both have basalt from geologic activity too! If you see any features at all, you are doing really well.

So what’s with the perihelic label? All orbits of all celestial objects are elliptical, or oval, in shape. Some orbits are almost all round, some are very elliptical, like a comet’s. None are circular as there is always something affecting them gravitationally. The point in an orbit in which the object is closest to what it is orbiting, like a planet orbiting the Sun, is called perihelion, or closest approach to the Sun. When you combine opposition with its perihelion, then Mars, in this case, is even closer to Earth. Again, it will never be very close. It will just allow us to see Mars a tiny bit larger than a regular opposition.

This event has one more aspect that is to our favor. The planet will be seen high in the sky in the Earth’s northern hemisphere. This allows us to see it higher above the Earth’s murky and turbulent atmosphere. Maybe even smaller features can be spied on this “red” planet. Look at the accompanying illustration and see the small change in the apparent size of Mars and compared to the Moon, all to scale and through a telescope. If you desire a more complete explanation of the orbits of Mars and why it looks larger, please see the October 2020 issue of the Bays Mountain Astronomy Club’s newsletter.

Public Observing Programs – Cancelled Until Further Notice

Our observing programs are free for everyone!

Quick View:

• Solar viewing (SunWatch) is free and held each clear Saturday & Sunday on the dam from 3-3:30 p.m., March-October.
• Night viewing (StarWatch) is held each Saturday in the months of March, April, October, & November, starting at dusk at the observatories. If poor weather, an alternate live presentation will occur in the planetarium theater.

Please check the calendar for the next daytime or nighttime viewing session.

Note: For the evening observing sessions, be sure to dress warmly. Dress for temperatures that are 20° colder than you expect.

The Bays Mountain Observatories are located along Bays Mountain Park Road just up from the dam. Look for the small circular building with a domed top. Please park in the parking lot and walk along the gravel drive to reach the observatory grounds.