APOD: Mars, Ceres, Vesta (2014 Apr 10)

[APOD Robot]

Mars, Ceres, Vesta

Explanation: That bright, ruddy star you've recently noticed rising just after sunset isn't a star at all. That's Mars, the Red Planet. Mars is now near its 2014 opposition (April 8) and closest approach (April 14), looping through the constellation Virgo opposite the Sun in planet Earth's sky. Clearly outshining bluish Spica, alpha star of Virgo, Mars is centered in this labeled skyview from early April, that includes two other solar system worlds approaching their opposition. On the left, small and faint asteroid Vesta and dwarf planet Ceres are seen near star Tau Virginis. But you'll just have to imagine NASA's Dawn spacecraft cruising between the small worlds. Having left Vesta in September of 2012, Dawn's ion engine has been steadily driving it to match orbits with Ceres, scheduled to arrive there in February 2015. Of course, you can also look near Mars for the Moon opposite the Sun in Earth's sky on the night of April 14/15 ... and see a total lunar eclipse.

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[Boomer12k]

And they watch us with Envious Eyes.....


Nice depiction of things.

:---[===] *

[orin stepanek]

I like the way Ceres and Vesta were circled; I never would have found them on my own!

[BDanielMayfield]

I like the way Ceres and Vesta were circled; I never would have found them on my own!

Yes. I wonder what their apparent magnitudes are? Looks like they might be easy to find with binoculars.

[neufer]

I like the way Ceres and Vesta were circled; I never would have found them on my own!

Yes. I wonder what their apparent magnitudes are? Looks like they might be easy to find with binoculars.

• Vesta should be magnitude ~5 and Ceres ~7.

---

Where is Dawn Now?

Want to know how far away Dawn is, or how fast it is traveling? These questions have multiple answers since the answer depends on what you use as a reference frame.

The Dawn trajectory is color-coded to provide information about when Dawn is using one of its ion thrusters and when it is coasting. The orbits of Earth, Mars, Vesta and Ceres are also given. The other four views use Dawn as a reference point, as if you were near the spacecraft looking at the Sun, Ceres, Earth, and Vesta. These views show the spacecraft in its true orientation as though you were viewing each given object. If the plasma trail is present, an ion thruster is operating; if the trail is not present, Dawn is coasting. The images are updated regularly with time given in UTC.

[CURRAHEE CHRIS]

Very timely picture for me as I think I am beginning to apply some of the things I am learning from this forum to actual skywatching- I live in Pennsylvania- would Spica be visible to the naked eye? I believe it has been (when we've had clear skies) the last couple evenings. Could someone confirm that it would be possible to see Spica with the naked eye? If so, I will feel happy as I have learned and applied some new knowledge.

[neufer]

Click to play embedded YouTube video.

[BMAONE23]

Very timely picture for me as I think I am beginning to apply some of the things I am learning from this forum to actual skywatching- I live in Pennsylvania- would Spica be visible to the naked eye? I believe it has been (when we've had clear skies) the last couple evenings. Could someone confirm that it would be possible to see Spica with the naked eye? If so, I will feel happy as I have learned and applied some new knowledge.

Spica (α Vir, α Virginis, Alpha Virginis, pronounced /ˈspaɪkə/) is the brightest star in the constellation Virgo, and the 15th brightest star in the night sky. It is a blue giant and a variable star of the Beta Cephei type located 260 light years from Earth.

At an apparent magnitude of just over +1, and being the 15th brightest star in the night sky. Spica is clearly Naked Eye visible

[CURRAHEE CHRIS]

At an apparent magnitude of just over +1, and being the 15th brightest star in the night sky. Spica is clearly Naked Eye visible

Thank you for that. I feel like an accomplished star gazer now!! Spica will now hold a very treasured spot in my newborn star gazing career. Outside of the little dipper and Orion's belt, this is the first object i've learned about and been able to find in the sky. Wish I could go back to the Lowell Observatory, find the professor who said "you are smart enough to do this" (when I told him this was a hobby well over my IQ) and tell him I did it- this one time!!

Best regards
CC

[Anthony Barreiro]

This is a lovely picture, and a very exciting astronomical conjunction! I've been watching Vesta and Ceres in 56 mm binoculars for the past few weeks. At 6th magnitude Vesta is easy to identify even in my light polluted city. Ceres has brightened from 8th to 7th magnitude, but is still tough to pick out in the city. On Saturday night our astronomy club had our monthly public star party at a less light-polluted location, and that helped, but there's still a lot of stars that are about as bright as Ceres in a binocular field of view. I hope To have a few clear nights in a row so I can sketch and see which star moves.

[Anthony Barreiro]

At an apparent magnitude of just over +1, and being the 15th brightest star in the night sky. Spica is clearly Naked Eye visible

Thank you for that. I feel like an accomplished star gazer now!! Spica will now hold a very treasured spot in my newborn star gazing career. Outside of the little dipper and Orion's belt, this is the first object i've learned about and been able to find in the sky. Wish I could go back to the Lowell Observatory, find the professor who said "you are smart enough to do this" (when I told him this was a hobby well over my IQ) and tell him I did it- this one time!!

Best regards
CC

Chris, knowing the sky and learning astrophysics are very different skills. They both have their pleasures. I personally find skywatching inherently enjoyable, while anything that involves math provides more of a deferred gratification. But even the math is starting to grow on me.

Congratulations as you start to create your mental map of the sky, and your personal calendar of the year.

[MarkBour]

Okay, speaking of math, and the Dawn spacecraft, I have a very basic orbital mechanics question. Actually, I'm not wanting the equations, just the qualitative description. Let's say I'm the Dawn spacecraft and I'm orbiting the Sun, a little ways in front of or behind the Earth, but in an identical orbit. Now, let's say I turn on my thruster to increase my forward motion. What happens? I believe I go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion. And oddly enough, although I accelerated "forward" and increased my forward rotational velocity (e.g. in km/s) around the Sun, instead of catching up to Earth, since I am now in a larger orbit, I will have watched the Earth pull ahead of me, in its steady journey around the Sun. So my rotational velocity in terms of degrees/s around the Sun actually decreased. Is that correct? So, in the diagram in the link to the Dawn spacecraft's mission, the transfer orbits actually show Dawn kind of backpedalling away from the planet it is at, as it transfers outward to a more Sun-remote planet's orbit?

It's counter-intuitive to me. Does anyone have a simulator for it?

[FloridaMike]

Okay, speaking of math, and the Dawn spacecraft, I have a very basic orbital mechanics question. Actually, I'm not wanting the equations, just the qualitative description. Let's say I'm the Dawn spacecraft and I'm orbiting the Sun, a little ways in front of or behind the Earth, but in an identical orbit. Now, let's say I turn on my thruster to increase my forward motion. What happens? I believe I go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion. And oddly enough, although I accelerated "forward" and increased my forward rotational velocity (e.g. in km/s) around the Sun, instead of catching up to Earth, since I am now in a larger orbit, I will have watched the Earth pull ahead of me, in its steady journey around the Sun. So my rotational velocity in terms of degrees/s around the Sun actually decreased. Is that correct? So, in the diagram in the link to the Dawn spacecraft's mission, the transfer orbits actually show Dawn kind of backpedalling away from the planet it is at, as it transfers outward to a more Sun-remote planet's orbit?

It's counter-intuitive to me. Does anyone have a simulator for it?

A really fun way to get to a more intuitive understanding of orbital dynamics is to read "The Smoke Ring" series by Larry Niven

EDIT ** The first book is called "The Integral Trees" **

[neufer]

Let's say I'm the Dawn spacecraft and I'm orbiting the Sun, a little ways in front of or behind the Earth, but in an identical orbit. Now, let's say I turn on my thruster to increase my forward motion. What happens? I believe I go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion. And oddly enough, although I accelerated "forward" and increased my forward rotational velocity (e.g. in km/s) around the Sun, instead of catching up to Earth, since I am now in a larger orbit, I will have watched the Earth pull ahead of me, in its steady journey around the Sun. So my rotational velocity in terms of degrees/s around the Sun actually decreased. Is that correct? So, in the diagram in the link to the Dawn spacecraft's mission, the transfer orbits actually show Dawn kind of backpedaling away from the planet it is at, as it transfers outward to a more Sun-remote planet's orbit?

A normal spacecraft would indeed "go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion." Since its orbital period is now longer it will, indeed, watch the Earth eventually catch up and pass it (angularly) "from below" (i.e., closer to the sun) before reaching its aphelion.

However, the Dawn spacecraft produces a constant thrust such that it continues to spiral out. You will watch the Earth eventually catch up and pass you (angularly) from below (i.e., closer to the sun) but it will take somewhat longer.

[NGC3314]

[

A really fun way to get to a more intuitive understanding of orbital dynamics is to read "The Smoke Ring" series by Larry Niven

EDIT ** The first book is called "The Integral Trees" **

Niven's inimitable short form:

East takes you Out, Out takes you West, West takes you In, In takes you East.

(This applies to definitions such that orbits go west-to-east, as almost all Earth satellites and large solar system objects do).

[MarkBour]

. . . the Dawn spacecraft produces a constant thrust such that it continues to spiral out. You will watch the Earth eventually catch up and pass you (angularly) from below (i.e., closer to the sun) but it will take somewhat longer.

Thanks for the reply, and verification! I had heard of an ion thruster as a really far-out sci-fi idea when I was young. Then it never seemed to have materialized after many years as a practical technology. Bravo, NASA!

... Oh, and yes, I think it's high time I went and read some Larry Niven.

[Anthony Barreiro]

Niven's inimitable short form:

East takes you Out, Out takes you West, West takes you In, In takes you East.

(This applies to definitions such that orbits go west-to-east, as almost all Earth satellites and large solar system objects do).

Oh, that's brilliant. I've got my koan for the day.

[neufer]

Let's say I'm the Dawn spacecraft and I'm orbiting the Sun, a little ways in front of or behind the Earth, but in an identical orbit. Now, let's say I turn on my thruster to increase my forward motion. What happens? I believe I go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion. And oddly enough, although I accelerated "forward" and increased my forward rotational velocity (e.g. in km/s) around the Sun, instead of catching up to Earth, since I am now in a larger orbit, I will have watched the Earth pull ahead of me, in its steady journey around the Sun. So my rotational velocity in terms of degrees/s around the Sun actually decreased. Is that correct? So, in the diagram in the link to the Dawn spacecraft's mission, the transfer orbits actually show Dawn kind of backpedaling away from the planet it is at, as it transfers outward to a more Sun-remote planet's orbit?

A normal spacecraft would indeed "go into an elliptical orbit, with Earth's orbit as the perihelion and some larger distance as the aphelion." Since its orbital period is now longer it will, indeed, watch the Earth eventually catch up and pass it (angularly) "from below" (i.e., closer to the sun) before reaching its aphelion.

However, the Dawn spacecraft produces a constant thrust such that it continues to spiral out. You will watch the Earth eventually catch up and pass you (angularly) from below (i.e., closer to the sun) but it will take somewhat longer.

[size=150][color=#0000FF]Ignoring mass loss Dawn follows a lituus trajectory[/color][/size]

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<<In mathematics, a lituus is a spiral in which the angle is inversely proportional to the square of the radius (as expressed in polar coordinates).



The curve was named for the ancient Roman lituus by Roger Cotes in a collection of papers entitled Harmonia Mensurarum (1722), which was published six years after his death.>>

[Joe Stieber]

I like the way Ceres and Vesta were circled; I never would have found them on my own!

Yes. I wonder what their apparent magnitudes are? Looks like they might be easy to find with binoculars.

I'm not certain when the picture was taken, but based on the positions of the asteroids and Mars, I'm guessing it would have been around April 3rd or April 4th. In that case, (4)Vesta is just below magnitude 6 and (1)Ceres is about magnitude 7, so they are indeed easy binocular objects, except where there is heavy light pollution. From my suburban home, it's no problem to see them with 10x42 binoculars (I've been following their movement for the past few weeks), but last night from center-city Philadelphia, it was difficult to see Vesta with 8x42 binoculars and I could not conclusively see Ceres (besides my center-city location amidst illuminated tall buildings, there was a gibbous moon in the sky and the asteroids were still somewhat low in altitude at 10 pm local time).

On the other hand, from a dark site, Vesta is visible with unaided eyes when it's near opposition (which it will be on April 13, 2014). I spotted it without optical aid on Sunday morning, April 6th, from the reasonably dark New Jersey Pine Barrens around 2 am, when they were near the meridian and after the moon had set. Vesta was at magnitude 5.8, which is within the nominal 6th magnitude limit for unaided eyes. One difficulty is the glare from nearby Mars -- it was necessary to use my outstretched hand to block it.

[BDanielMayfield]

Thanks for that encouraging report Joe. I'll try to see these for myself, when the clouds allow.

Bruce