Well, last night was our chance to get out of our burrows and look for the Lyrid meteor shower. Hmm, didn't see anything, but can report on SpaceX Starlink launch and HoliCOW, what's up with the Hubble Constant, H0?
The weather was very good for nighttime observing, but we were pretty much stuck with city lights polluted viewing since it was not the best thing to drive off into the countryside at midnight, although it is hard to imagine what pandemic risk this was going to expose us or others. This Sky Safari Pro screenshot shows the location of the meteor shower radiant.
|We can use Vega to identify the radiant for the Lyrid meteor shower (Source: Sky Safari Pro)|
So, now we know where to look, but how bright is the shower supposed to be and will we be able to see it through our city lights view? Well, one estimate of magnitude +2 gives us some hope. I can barely see Polaris which also comes in at magnitude 2, but maybe we can just rely on long time exposures with the DSLR to capture some meteors.
|The predicted visual magnitude of the Lyrids should be eyeball visible in city lights (Source: Wikipedia)|
So, somehow, I managed to stay awake until midnight and then stumbled outside with flimsy tripod and DSLR. This image below is one of 10 images, taken with 120 second exposure, with some enhanced stretching in Photoshop. You can see that without a tracking mount and even with a 55 mm lens setting, you can see star trails. The brighter streak at the far left is the star Vega. Sadly, I didn't capture any meteor trails in any of the images, even though a lot of the dim background stars showed up just fine. Anybody else have better luck b maybe staying up a few more hours?
|Looking at the Lyrid radiant, 55mm DSLR, ISO 200, 120 second exposure (Source: Palmia Observatory)|
Just to make sure the camera was pointing in the right direction, the image was sent to Astrometry.net and the plate solved solution shows the pointing angles were just fine. The center of the image was just a couple of degrees from the RA and Dec of the radiant.
|Double checking the camera pointing position with Astrometry.net (Source: Palmia Observatory)|
In other space news, SpaceX has still been busy and has managed to launch another batch of Starlink satellites. So the pandemic has not slowed that activity down much but we are not going to be able to travel to any launch site to view a launch for any time soon. At least in the past, we had opportunities to witness actual launches with our own eyeballs and that was very exciting. If you want to check out our experience of a Falcon 9 launch form Vandenberg AFB, check out the blog posting of October 8, 2018, and for the experience of the first Falcon Heavy launch from Kennedy Space Center, check out the posting from February 8, 2018.
|April 22 launch of the next batch of Starlink satellites from KSC (Source: @SpaceX)|
This latest batch of satellites will not be visible initially here in Orange County, or probably over much of Southern California, until a few days after launch. The prediction is that they will still be eyeball visible, at magnitude 3.7, but will be quite low in the sky. So, check out the prediction from Heavens-Above and take a chance and leave your burrow to take a look up in the sky at about 8:42 local time.
|Next Starlink viewing opportunity in Orange County area is Sunday, April 26 (Source: heavens-above.com)|
Other SpaceX news includes this photo of SN4 being transported down and across the road from the assembly area to the launch area. Thanks for this foggy and early morning photo of ongoing activity, Mary!
|Starship SN4 being transported across the road to the launch site (Source: @BocaChicaGal)|
Finally, let's review another interesting presentation from the virtual APS April 2020 meeting. Hubble's Constant is a key astronomical parameter and the precision with which it is measured has been increasing ever since it was first measured. Now, every discussion of Hubble's constant revolves around the "tension" between two different measured values by two different methods, which are the CMB method and the Supernovae method. The first method makes measurements of the CMB, which were put in place shortly after the Big Bang, and the Supernovae method makes measurements of how the universe seems to be at the current time. Now, this HOLiCOW method is a third independent way of measuring Hubble's constant. In this screenshot from Kenneth Wong's presentation you can see what the acronym means.
|HOLiCOW Collaboration uses time delay cosomography (Source: K. Wong, APS April 2020 meeting)|
Remember that the CMB data from the Planck satellite was used to establish the Hubble constant at 67.4 km/sec per megaparsec and the supernova data set the constant at 74.0 km/sec per megaparsec. Hmm, not much difference and both values are within about 10%, but an error analysis indicates that two estimates are in violent disagreement. Trying to resolve this disagreement has a lot of astronomers busy looking into possible error sources or even new physics to try to explain and resolve the difference.
|HOLiCOW is an independent way of estimating the Hubble constant (Source: K. Wong, APS April 2020 meeting)|
HOLiCOW uses gravitation lensing to provide a separate independent way of making the measurement. The supernovae method needs to establish good estimate of the distances involved in order to measure the constant and making distance measurements is the most difficult. Gravitation lensing can be used to estimate distances without relying on the distance ladder established over many years, starting probably with Cepheid variable distance correlations.
|HOLiCOW uses gravitational lensing to measure Hubble constant (Source: K. Wong, APS April 2020 meeting)|
Gravitational lensing can be used to see dim distant galaxies because of the brightening effect of the foreground lensing galaxy. Being able to look back over very large distances will show the effect of the expansion of the universe, but some corrections to the lensed image need to be done to establish the true distance. HOLiCOW uses time-delay cosmography to accomplish this correction. They look for small varying brightness changes in the distant source and then by comparing the time delay as seen by different paths taken by the distant source as the light moves passed the lens. By comparing these different time delays, it is possible to get better distance correction.
|How HOLiCOWto uses time delay cosmography to measure Hubble constant (Source: K. Wong, APS April 2020 meeting)|
So, the HOLiCOW collaboration applies these and other corrections to get a separate, independent estimate of distance and from that a separate estimate of Hubble's constant for the expansion of the universe. So, in this screenshot we see that the HOLiCOW estimate lines up pretty well with the supernovae measurements by the SHOES collaboration. So what do we make of this additional measurement? Is there some fundamental difference between CMB estimate, which was pretty much fixed shortly after the Big Bang, and measurements made today using supernova distance estimates?
|HOLiCOW, a late time probe, shows Hubble constant of 73.3 (Source: K. Wong, APS April 2020 meeting)|
The controversy and research goes on. As the measurement of the Hubble constant keeps getting better and better, other cosmological theories and theories of inflation will face tougher times as they must be consistent with the better estimate of Hubble constant.
|HOLiCOW is an independent estimate of H0, consistent with SNe estimates (Source: K. Wong, APS April 2020 meeting)|
Until next time, here from our burrow, stay sane, stay safe,
Resident Astronomer George
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