Once again, I am here with a factual question from my mom.
So, there’s a moon in the sky. And there’s a lot of stars. Now, one star in particular (or maybe it’s a planet?) is right next to the moon. It’s always next to the moon. But, the star is not always in the same place. Sometimes, it’s at 2:00. Right now, it’s at 6:30. Can anyone tell us why?
As you can probably tell, my public school education never actually left the planet. The closest we came to actual Astronomy was being told that the earth was not the center of the universe. I don’t even fully understand why we have phases of the moon. So, for my own benefit, can someone explain that bit too?
Any other random info you might want to add will be appreciated also.
There is no single object which is always next to the Moon for the simple reason that the Moon follows a unique path through the sky. Now, the Moon lies roughly on the plane of the ecliptic, so there is often one or more planets near it as well as any of several stars throughout the year. Most likely, your mother is noticing a bright object somewhere in the vicinity of the Moon and assuming it’s the same object each time.
Over a given night, there may be a planet (or two or three) in conjunction with the moon, & the moon orbits quickly enough that its exact position relative to the planets will visibly change in an hour or so, & pass out of conjunction in a day or so.
I asked my mom. She said that somewhere near the moon, just at different locations, there is always one very bright, clear object. She said it’s always very close to the same distance away. Since it’s so bright, clear and so close to the moon (just in different locations) she assumed it was the same object all the time. I looked and I can’t even tell if it is a star, a planet, a satellite, or God. I don’t know a thing about what is out there. If my camera has a working battery, I’ll post a picture of it when I get home. I’m pretty sure that one of you will be able to tell me exactly what it is just by looking at a picture.
The ancients spent a lot of time outdoors at night (what with TV not being invented yet), and they noticed something weird. Most stars move across the sky in a fixed pattern. Except for a few wandering stars that would move independently of the fixed stars. And the moon and sun also move against the pattern of fixed stars.
They called the class of wandering stars “planets”, and named them after the gods. We still call them Mercury, Venus, Mars, Jupiter and Saturn. They didn’t notice Uranus or Neptune because you really need a telescope to seem them.
So. The Sun is in the center of the solar system. We now know that the Earth and the other planets (of course the ancients didn’t know that the Earth was a planet too) go around the sun in nearly circular orbits. The moon orbits around the Earth. It takes about 30 days for the Moon to completely orbit the Earth. Yes, that’s where we get the concept of a “Moonth”. So no planet will remain in the same position with regards to the Moon, and the Moon will travel across the background of the fixed stars every 30 days.
And the Moon will change phases, with a whole cycle lasting 30 days. The phases of the moon are caused by the Sun shining on the Moon. When the sun is roughly behind the Earth it shines directly on the side of the Moon nearest us, so we see the whole bright side, and that’s the full moon. When the Sun is to the side, we see half the lit side and half the shadow side, a half moon. And when the Sun is roughly behind the Moon, we see the shadow side, a New Moon. A full moon will be roughly opposite the Sun in the sky, while a new moon will be close to the sun.
Nope. If your mom lives someplace fairly rural with dark night skies, then on a clear night she can probably always see at least one star or planet fairly close to the moon. But it’s not the same object every time. If she observes systematically—say, going out and looking at the moon at the same time each night for a week or so—she’ll probably see that the “companion objects” she’s noticing near the moon are actually quite different from one another in brightness, clarity and distance from the moon.
Indeed, and quite pretty tonight in my area. It’s worth noting that right now they’re both near the western horizon and bright enough to shine when no other stars are yet visible
She could always use: www.skyviewcafe.com. Type in your location, the date and the time and you can see the orientation of the moon, all the planets and many of the brighter stars.
Here are two more sites explaining the moon phases.
simple less simple
An easy way to visualize the moon phases is to hold a ball (the moon) in your outstretched hand with a bright light (your sun) coming for one direction. Now, you (the earth) turn in a circle, watching the light change on the ball.
A mirror is usually sufficient for the first.
Yep, old joke. Pointless, juvenile, even purile. But it had to be done.
Additional question - how bright is the moon relative to other astronomical objects. I only ask because I noticed a star right next to a really bright full moon just the other day, and it triggered the question.
You guys are awesome. Thanks for all the information. I finally understand the phases of the moon (and I didn’t even have to click any links, your descriptions were excellent). I called my mom and told her to check out the links in the thread.
Dr. Lao , Your link was so cool. I just told my mom about it. When I played around with it, I was so excited to see how by looking at the orbits of the moon and Venus, you can see how they might appear to be located right next to each other, but also how their orientation might change. Which is exactly what my mom has been noticing.
So thanks again guys. This is the third time I’ve relayed one of my mom’s questions and once again, she’s totally satisfied. I think she’s going to actually start using her own username instead of going through me - because she has a lot of questions. She’s a very curious person.
Note that because Venus’ orbit is within ours, it stays fairly close to the sun in the sky, swapping between being the morning star and the evening star. The full moon will be opposite the sun in the sky, so it can’t be anywhere near Venus. You’ll only see the moon near Venus when it’s a crescent like now. (A new moon could be near Venus, but you can’t see a new moon anyway except during an eclipse.) Of course by “near”, I mean from our visual perspective.