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NASA to launch space observatory that will map 450M galaxies

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Re: NASA to launch space observatory that will map 450M galaxies

#101

Post by JKCalhoun »

mturmon wrote: post #79
dylan604 wrote: post #7

"The SPHEREx mission will map the entire sky four times over two years, offering scientists a chance to study how galaxies form and evolve, and providing a window into how the universe came to be." So each object will be scanned ~6 months from the previous scan. How much evolving within the universe will be noticeable within that 2 year run? My gut response is not much, but that's why we do the science to see the cha…

A nearby (excellent) comment ( https://news.ycombinator.com/item?id=43338459 ) gives further context, but: the 6-month revisit period is just an artifact of the Earth-orbit-based sky scanning strategy. In 6 months the satellite, precessing at 1 degree/day, and facing away from the sun during data collection, will scan the sky completely. (See Fig 1 of the paper [0]). So in particular, the 6-month period is not to rev…

Any chance there will be enough "parallax" in the 6-month period to get a stereo-distancing map for the galaxies? Or do we already have that from red-shift, relative luminance or some other means?

Re: NASA to launch space observatory that will map 450M galaxies

#102

Post by DiogenesKynikos »

JKCalhoun wrote: post #99
eleveriven wrote: post #83

It's pretty incredible to think that we're at a point in human history where we can map 450 million galaxies and probe the origins of the universe

And to think I assumed Astronomy was a stagnant field some decades ago. I have no idea why I thought that. Maybe that optical resolution from ground-based telescopes was not going to advance orders of magnitudes? Maybe I didn't think the sciences would continue to get money for space telescopes?

Astronomy has been in a golden age for the last 35 years, based on:

1. Digital cameras, and the computers to analyze images.

2. Space telescopes (Hubble Space Telescope, the first large space telescope, only launched in 1990).

3. The building of massive ground-based telescopes. Before 1990, the largest telescope had a mirror diameter of 6 meters. Now, multiple 30-meter telescopes are under construction. Collecting power goes with the square of the diameter, so this is an increase of 25 times in collecting power!

4. Very recently, the development of gravitational-wave interferometers, which allow astronomers to observe a totally new type of radiation.

Re: NASA to launch space observatory that will map 450M galaxies

#103

Post by igleria »

jimkleiber wrote: post #97
eleveriven wrote: post #83

It's pretty incredible to think that we're at a point in human history where we can map 450 million galaxies and probe the origins of the universe

I feel infinitesimally small.

me too, but big things have small beginnings!

Re: NASA to launch space observatory that will map 450M galaxies

#104

Post by DiogenesKynikos »

dylan604 wrote: post #7

"The SPHEREx mission will map the entire sky four times over two years, offering scientists a chance to study how galaxies form and evolve, and providing a window into how the universe came to be." So each object will be scanned ~6 months from the previous scan. How much evolving within the universe will be noticeable within that 2 year run? My gut response is not much, but that's why we do the science to see the cha…

Most things astronomers observe do not change much over the course of 6 months. For comparison, it takes the Sun about 200 million years to orbit around the center of the Milky Way once, so a galaxy like the Milky Way would hardly change in 6 months.

However, there is an entire field of astronomy, called "time-domain astronomy," that deals with things that do change on human timescales. There are pulsating stars, supernovae, galaxies with rapidly accreting central black holes, and many other types of objects. Surveys that focus on the "time domain" have survey strategies that are tailored to whatever type of object they're looking at. For example, if you're looking for planets that transit in front of their host stars, you should look every ~30 minutes or so, because planet transits only last around that amount of time.

Re: NASA to launch space observatory that will map 450M galaxies

#105

Post by perihelions »

JKCalhoun wrote: post #101
mturmon wrote: post #79

Earlier quoted context omitted.

A nearby (excellent) comment ( https://news.ycombinator.com/item?id=43338459 ) gives further context, but: the 6-month revisit period is just an artifact of the Earth-orbit-based sky scanning strategy. In 6 months the satellite, precessing at 1 degree/day, and facing away from the sun during data collection, will scan the sky completely. (See Fig 1 of the paper [0]). So in particular, the 6-month period is not to rev…

Any chance there will be enough "parallax" in the 6-month period to get a stereo-distancing map for the galaxies? Or do we already have that from red-shift, relative luminance or some other means?

Andromeda (the nearest) is 2e19 km away and has a relative motion of 300 km/s in the radial direction. If we assume the tangential motion is similar, that's 5e9 km of tangential displacement over 6 months, for a total angular displacement of 5e-5 arcseconds (50 microarcseconds).

That's well below the precision of every telescope. (Admittedly GAIA, the one designed for parallax measurements, comes close, but its techniques only work on very bright point-source objects).

I think these articles answer your question:

https://en.wikipedia.org/wiki/Cosmic_distance_ladder

https://news.ycombinator.com/item?id=43151943 ("Part two of Grant Sanderson's video with Terry Tao on the cosmic distance ladder (mathstodon.xyz)", 99 comments)

Re: NASA to launch space observatory that will map 450M galaxies

#106

Post by nuccy »

DiogenesKynikos wrote: post #102
JKCalhoun wrote: post #99

Earlier quoted context omitted.

And to think I assumed Astronomy was a stagnant field some decades ago. I have no idea why I thought that. Maybe that optical resolution from ground-based telescopes was not going to advance orders of magnitudes? Maybe I didn't think the sciences would continue to get money for space telescopes?

Astronomy has been in a golden age for the last 35 years, based on: 1. Digital cameras, and the computers to analyze images. 2. Space telescopes (Hubble Space Telescope, the first large space telescope, only launched in 1990). 3. The building of massive ground-based telescopes. Before 1990, the largest telescope had a mirror diameter of 6 meters. Now, multiple 30-meter telescopes are under construction. Collecting po…

To add to the list (the order is arbitrary):

5. Advances in the multi-messenger observations, where apart of photons and gravitational waves, astronomers can detects also neutrinos with specialized neutrino detectors, e.g.: IceCube [a], though there are many more of those [b].

6. Advances in very-long-baseline interferometry [c] using a globe-sized array of radio-telescopes, like Event Horizon Telescope [d]

[a] https://en.wikipedia.org/wiki/IceCube_Neutrino_Observatory

[b] https://en.wikipedia.org/wiki/Neutrino_detector or here https://en.wikipedia.org/wiki/List_of_neutrino_experiments

[c] https://en.wikipedia.org/wiki/Very-long-baseline_interferome...

[d] https://en.wikipedia.org/wiki/Event_Horizon_Telescope

Re: NASA to launch space observatory that will map 450M galaxies

#110

Post by indoordin0saur »

numpad0 wrote: post #91
indoordin0saur wrote: post #37

Earlier quoted context omitted.

Everything launches on a Falcon these days. No one else can catch up in terms of safety cost or speed.

I'm not sure how to make out of comments like this. Is SpaceX actually launching customer payloads under $50m or whatever? Because, unless they are, it won't be long before JAXA/MHI starts selling H3 at half the cost of H-IIA, which is already like 15t to LEO for $67m at 150 JPY/USD, which leaves F9 reusable barely competitive in price. I don't know what India or China charge for foreign customers, but is it really r…

> Is that really a meaningful statement that stands, or it that just hand wavy glance away one now?

The $67m figure is the same one I'm finding for Falcon 9 (and it can carry loads 40% heavier). That made me think they were matching each other on price to stay competitive in the market and that seems correct as the internal costs I'm seeing for SpaceX Falcon 9 launches are estimated around $15mil, meaning they have a large margin from which to come down from.

> it won't be long before JAXA/MHI starts selling H3 at half the cost of H-IIA

SpaceX doesn't stand still. It's weird to think that in several years SpaceX will be in the same place (relying on Falcon 9) yet JAXA, etc will have improved dramatically.

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