the hubble

anonymous asked:

How do scientists measure the distance of far off celestial objects? I know light years are the standard measurement for vast cosmic distances and I know what a light year is, but how do scientists figure it out? How do they figure out Alpha Centauri is exactly 4.3 light years from Earth for example?

Hello and thanks for asking! There are several ways that we determine distance to stars.

If you hold your finger out in front of you and close one eye, it appears in one spot. Now, close that eye and open the other. It looks like your finger has shifted position!! This is because each eye is looking at your finger from a slightly different angle, giving it a slightly different apparent location. We can do this with stars too - scientists take a picture of a star’s location when the earth is on one side of its orbit, and another when the earth is on the other side. Looking at how far the star appeared to shift over the course of six months, we can calculate its distance from us, using trigonometry and similar triangles. Since the distances involved are so large, we can approximate the distance using the formula d=1/p, where d is distance in parsec and p is the parallax angle, in arcseconds (a measure of distance across the sky) (image source)

Standard Candle
Now, what about stars that are too far away to have a visible parallax angle (stars further than a few hundred light years away)? For distances this far, we use type 1a supernovae, which are called standard candles because they have essentially a standard luminosity. Using its observed brightness, we can calculate the distance it is (and the objects around it, like nearby galaxies). 

Spectra, other stars
We can also look at the spectrum of a star, classify its type, and from there estimate its luminosity. Based on our estimated luminosity, we can calculate the distance it would have to be to give us that observed brightness. This isn’t that accurate, by the way, and just yields an estimate.
We can also look at different types of stars (Cepheid variables), which have specific brightnesses. Based on their observed brightnesses and expected luminosities,we can calculate its distance (and the distance of nearby objects).

Hubble Constant
Now, some galaxies are so far away that their light is actually redshifted by the expansion of the universe! By looking at the spectrum of a galaxy, and looking at how far the spectral lines emitted by specific elements have shifted in the red direction, we can calculate its apparent recessional velocity (how fast it’s moving away from us). Then, we can solve for how far away it is given the Hubble constant: (image source)

So yeah, that’s how we determine distances to cosmic objects.Let me know if you have any other questions!! I’m happy to answer them.

Ocean Worlds Beyond Earth

We’re incredibly lucky to live on a planet drenched in water, nestled in a perfect distance from our sun and wrapped with magnetic fields keeping our atmosphere intact against harsh radiation and space weather.

We know from recent research that life can persist in the cruelest of environments here on Earth, which gives us hope to finding life thriving on other worlds. While we have yet to find life outside of Earth, we are optimistic about the possibilities, especially on other ocean worlds right here in our solar system.  

So…What’s the News?!

Two of our veteran missions are providing tantalizing new details about icy, ocean-bearing moons of Jupiter and Saturn, further enhancing the scientific interest of these and other “ocean worlds” in our solar system and beyond!

Cassini scientists announce that a form of energy for life appears to exist in Saturn’s moon Enceladus, and Hubble researchers report additional evidence of plumes erupting from Jupiter’s moon Europa.

The Two Missions: Cassini and Hubble


Our Cassini spacecraft has found that hydrothermal vents in the ocean of Saturn’s icy moon Enceladus are producing hydrogen gas, which could potentially provide a chemical energy source for life.

Cassini discovered that this little moon of Saturn was active in 2005. The discovery that Enceladus has jets of gas and icy particles coming out of its south polar region surprised the world. Later we determined that plumes of material are coming from a global ocean under the icy crust, through large cracks known as “tiger stripes.” 

We have more evidence now – this time sampled straight from the plume itself – of hydrothermal activity, and we now know the water is chemically interacting with the rock beneath the ocean and producing the kind of chemistry that could be used by microbes IF they happened to be there.

This is the culmination of 12 years of investigations by Cassini and a capstone finding for the mission. We now know Enceladus has nearly all the ingredients needed for life as we know it.

The Cassini spacecraft made its deepest dive through the plume on Oct. 28, 2015. From previous flybys, Cassini determined that nearly 98% of the gas in the plume is water and the rest is a mixture of other molecules, including carbon dioxide, methane and ammonia. 

Cassini’s other instruments provided evidence of hydrothermal activity in the ocean. What we really wanted to know was…Is there hydrogen being produced that microbes could use to make energy? And that’s exactly what we found!

To be clear…we haven’t discovered microbes at Enceladus, but vents of this type at Earth host these kinds of life. We’re cautiously excited at the prospect that there might be something like this at Enceladus too!


The Hubble Space Telescope has also been studying another ocean world in our solar system: Europa!

Europa is one of the four major moons of Jupiter, about the size of our own moon but very different in appearance. It’s a cold, icy world with a relatively smooth, bright surface crisscrossed with dark cracks and patches of reddish material.

What makes Europa interesting is that it’s believed to have a global ocean, underneath a thick crust of ice. In fact, it’s got about twice as much ocean as planet Earth!

In 2014, we detected evidence of intermittent water plumes on the surface of Europa, which is interesting because they may provide us with easier access to subsurface liquid water without having to drill through miles of ice.

And now, in 2016, we’ve found one particular plume candidate that appears to be at the same location that it was seen in 2014. 

This is exciting because if we can establish that a particular feature does repeat, then it is much more likely to be real and we can attempt to study and understand the processes that cause it to turn on or off. 

This plume also happens to coincide with an area where Europa is unusually warm as compared to the surrounding terrain. The plume candidates are about 30 to 60 miles (50 to 100 kilometers) in height and are well-positioned for observation, being in a relatively equatorial and well-determined location.

What Does All This Mean and What’s Next?

Hubble and Cassini are inherently different missions, but their complementary scientific discoveries, along with the synergy between our current and planned missions, will help us in finding out whether we are alone in the universe. 

Hubble will continue to observe Europa. If you’re wondering how we might be able to get more information on the Europa plume, the upcoming Europa Clipper mission will be carrying a suite of 9 instruments to investigate whether the mysterious icy moon could harbor conditions favorable for life. Europa Clipper is slated to launch in the 2020s.

This future mission will be able to study the surface of Europa in great detail and assess the habitability of this moon. Whether there’s life there or not is a question for this future mission to discover!

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Glittering Frisbee Galaxy: This image from Hubble’s shows a section of a spiral galaxy located about 50 million light-years from Earth. We tend to think of spiral galaxies as massive and roughly circular celestial bodies, so this glittering oval does not immediately appear to fit the visual bill. What’s going on? Imagine a spiral galaxy as a circular frisbee spinning gently in space. When we see it face on, our observations reveal a spectacular amount of detail and structure. However, the galaxy frisbee is very nearly edge-on with respect to Earth, giving it an appearance that is more oval than circular. The spiral arms, which curve out from the galaxy’s dense core, can just about be seen.

Although spiral galaxies might appear static with their picturesque shapes frozen in space, this is very far from the truth. The stars in these dramatic spiral configurations are constantly moving as they orbit around the galaxy’s core, with those on the inside making the orbit faster than those sitting further out. This makes the formation and continued existence of a spiral galaxy’s arms something of a cosmic puzzle, because the arms wrapped around the spinning core should become wound tighter and tighter as time goes on - but this is not what we see. This is known as the winding problem.

Image credit: ESA/Hubble & NASA

For more information on this image, visit:

As if approaching in an intergalactic spaceship, I love the sense of grandeur captured in this zoomed-in view of NGC 5033. Lying some 40 million light-years away, it features an active and bright galactic nucleus that is thought to contain a supermassive black hole.

(Image Credit: NASA, ESA; Processing: Judy Schmidt)

In the winter of 1995, scientists pointed the Hubble Telescope at an area of the sky near the Big Dipper, a spot that was dark and out of the way of light pollution from surrounding stars. The location was apparently empty, and the whole endeavor was risky. What, if anything, was going to show up? Over ten consecutive days, the telescope took close to 150 hours of exposure of that same area. And what came back was nothing short of spectacular: an image of over 1,500 distinct galaxies glimmering in a tiny sliver of the universe. 

Now, let’s take a step back to understand the scale of this image. If you were to take a ballpoint pen and hold it at arm’s length in front of the night sky, focusing on its very tip, that is what the Hubble Telescope captured in its first Deep Field image. In other words, those 3,000 galaxies were seen in just a tiny speck of the universe, approximately one two-millionth of the night sky.

So the next time you stand gazing up at the night sky, take a moment to think about the enormity of what is beyond your vision, out in the dark spaces between the stars.

From the TED-Ed Lesson How small are we in the scale of the universe? - Alex Hofeldt

Animation by Yukai Du