The AAVSO SPP program includes a number of RR Lyrae stars and a few delta Scutid stars with large amplitudes, although data on any short period pulsating star can be submitted to the AAVSO International Database.  These stars typically have a small range, often less than one magnitude, so CCD observations are preferred over visual ones.  CCD observations should be through a standard filter to allow data sets to be merged together, and to minimize the effects due to the color changes these stars undergo during the pulsation cycle.  Many Cepheid stars are quite bright and photometry with a digital SLR or even a webcam is practical.  Refer to the information on DSLR photometry on the Citizen Sky site for more information.

RR Lyrae Ephemeris

Each year the AAVSO SPP Section issues a month-by-month prediction of times of maximum (ToMx) for selected RR Lyrae and large-amplitude delta Scuti stars.  This document lists times when each star will be at its maximum brightness.  (Hint:  to save these to your local system right-click and choose "Save link as")

RR Lyrae Ephemeris 2016
RR Lyrae Ephemeris 2015
RR Lyrae Ephemeris 2014
RR Lyrae Ephemeris 2013

RR Lyrae Ephemeris Generator

In addition to the PDF ephemeris above, an online ephemeris generator for RR Lyrae and delta Scuti stars is available.  This site allows the user to input their location and select a magnitude range, and generates a nightly list of stars that can be observed at the selected site.

Program Stars

The Table 1 lists some RR Lyrae stars that exhibit the Blahzko effect as well as some large-amplitude delta Scuti stars that have multiple periods. These stars should be observed several times every few seasons, at all phases (not just during maximum) to look for changes in the primary and Blazhko periods. The light curves for the multi-periodic delta Scuti stars are complex and vary markedly from cycle to cycle.  The RR Lyrae and delta Scuti stars in Table 2 appear to have single, stable periods without any Blazhko effect.  These need "time of maximum" (ToMx) measurements every few years to check for any changes in period that may occur.  Table 3 shows interesting Cepheid stars that have been observed by SPP section members.  Like the stars in Table 2, measuring the time of maximum should be done every few years for these stars.

Table 1 - RR Lyrae stars showing Blazhko effect, and multi-periodic delta Scuti stars
Variable Type Period (days)
Blazhko (days)
SW And RRab 0.4423 36.8

Has 2 or 3 periods
RS Boo RRab 0.3773 533
ST Boo RRab 0.6223 284
SW Boo RRab 0.5136 13
TV Boo RRc 0.3126 33.5
RW Cnc RRab 0.5472 87
TT Cnc RRab 0.5634 89
XZ Cyg RRab 0.4666 57.3
DM Cyg RRab 0.4199 26
RW Dra RRab 0.4429 41.6
XZ Dra RRab 0.4765 76
RR Gem RRab 0.3973 37
AR Her RRab 0.4700 31.6
DL Her RRab 0.5916 33.6
SZ Hya RRd 0.5372 25.8 Dual mode
VX Hya Delta Sct 2 periods
Has a strong beat period between the two periods
RZ Lyr RRab 0.5112 116.7
RV UMa RRab 0.4681 90.1
Note: because the behavior of AC And and VX Hya are so irregular, these stars do not appear in the AAVSO Ephemeris.

Table 2 - Non-Blazhko RR Lyrae stars and large-amplitude delta Scuti stars
Variable Type Period (days)
XX And RRab 0.7228
AT And RRab 0.6169
SW Aqr RRab 0.4593
TZ Aur RRab 0.3917
BH Aur RRab 0.4561
SZ Boo RRab 0.5228
TW Boo RRab 0.5323
UU Boo RRab 0.4569
UY Boo RRab 0.6510
RR Cet RRab 0.5530
TW Her RRab 0.3996
VX Her RRab 0.4554
DY Her Delta Sct 0.1486
UU Hya RRab 0.5239
DG Hya RRab 0.7542
DH Hya RRab 0.4890
RR Leo RRab 0.4524
SS Leo RRab 0.6263
TV Leo RRab 0.6729
WW Leo RRab 0.6029
SZ Lyn Delta Sct 0.1205 Part of a binary system.
AV Peg RRab 0.3904

Table 3 - Target Cepheids
Star Name Magnitude Range Period (days) Comment / Reference
Polaris (alpha UMi) 1.97 - 2.00 3.97 Amplitude has shrunk to almost zero in the last several decades but appears to be increasing now
beta Dor 3.46 – 4.08 9.843
T Mon 5.58 – 6.62 27.025 JAAVSO 4:84 (Landis 1975)
RT Aur 5.00 – 5.82 3.728
zeta Gem 3.62 – 4.18 10.151
ASAS182612 11.51 – 11.98 4.151 Eclipsing Cepheid; AAVSO Alert Notice #351
FF Aql 5.18 – 5.68 4.471
TT Aql 6.46 – 7.7 13.755 JAAVSO 4: 84 (Landis 1975)
U Aql 6.08 – 6.86 7.024
eta Aql 3.48 – 4.39 7.177
TW Cap 9.95 – 11.28 28.61 W Virginis type; JAAVSO, 10: 66 (DeYoung 1981)
delta Cep AB 3.48 – 4.37 5.366 Cepheid Prototype